src/HOL/Analysis/Convex_Euclidean_Space.thy
 author paulson Sun Apr 15 13:57:00 2018 +0100 (14 months ago) changeset 67982 7643b005b29a parent 67968 a5ad4c015d1c child 68024 b5e29bf0aeab child 68072 493b818e8e10 permissions -rw-r--r--
various new results on measures, integrals, etc., and some simplified proofs
```     1 (* Title:      HOL/Analysis/Convex_Euclidean_Space.thy
```
```     2    Author:     L C Paulson, University of Cambridge
```
```     3    Author:     Robert Himmelmann, TU Muenchen
```
```     4    Author:     Bogdan Grechuk, University of Edinburgh
```
```     5    Author:     Armin Heller, TU Muenchen
```
```     6    Author:     Johannes Hoelzl, TU Muenchen
```
```     7 *)
```
```     8
```
```     9 section \<open>Convex sets, functions and related things\<close>
```
```    10
```
```    11 theory Convex_Euclidean_Space
```
```    12 imports
```
```    13   Connected
```
```    14   "HOL-Library.Set_Algebras"
```
```    15 begin
```
```    16
```
```    17 lemma swap_continuous: (*move to Topological_Spaces?*)
```
```    18   assumes "continuous_on (cbox (a,c) (b,d)) (\<lambda>(x,y). f x y)"
```
```    19     shows "continuous_on (cbox (c,a) (d,b)) (\<lambda>(x, y). f y x)"
```
```    20 proof -
```
```    21   have "(\<lambda>(x, y). f y x) = (\<lambda>(x, y). f x y) \<circ> prod.swap"
```
```    22     by auto
```
```    23   then show ?thesis
```
```    24     apply (rule ssubst)
```
```    25     apply (rule continuous_on_compose)
```
```    26     apply (simp add: split_def)
```
```    27     apply (rule continuous_intros | simp add: assms)+
```
```    28     done
```
```    29 qed
```
```    30
```
```    31 lemma dim_image_eq:
```
```    32   fixes f :: "'n::euclidean_space \<Rightarrow> 'm::euclidean_space"
```
```    33   assumes lf: "linear f"
```
```    34     and fi: "inj_on f (span S)"
```
```    35   shows "dim (f ` S) = dim (S::'n::euclidean_space set)"
```
```    36 proof -
```
```    37   obtain B where B: "B \<subseteq> S" "independent B" "S \<subseteq> span B" "card B = dim S"
```
```    38     using basis_exists[of S] by auto
```
```    39   then have "span S = span B"
```
```    40     using span_mono[of B S] span_mono[of S "span B"] span_span[of B] by auto
```
```    41   then have "independent (f ` B)"
```
```    42     using independent_inj_on_image[of B f] B assms by auto
```
```    43   moreover have "card (f ` B) = card B"
```
```    44     using assms card_image[of f B] subset_inj_on[of f "span S" B] B span_inc by auto
```
```    45   moreover have "(f ` B) \<subseteq> (f ` S)"
```
```    46     using B by auto
```
```    47   ultimately have "dim (f ` S) \<ge> dim S"
```
```    48     using independent_card_le_dim[of "f ` B" "f ` S"] B by auto
```
```    49   then show ?thesis
```
```    50     using dim_image_le[of f S] assms by auto
```
```    51 qed
```
```    52
```
```    53 lemma linear_injective_on_subspace_0:
```
```    54   assumes lf: "linear f"
```
```    55     and "subspace S"
```
```    56   shows "inj_on f S \<longleftrightarrow> (\<forall>x \<in> S. f x = 0 \<longrightarrow> x = 0)"
```
```    57 proof -
```
```    58   have "inj_on f S \<longleftrightarrow> (\<forall>x \<in> S. \<forall>y \<in> S. f x = f y \<longrightarrow> x = y)"
```
```    59     by (simp add: inj_on_def)
```
```    60   also have "\<dots> \<longleftrightarrow> (\<forall>x \<in> S. \<forall>y \<in> S. f x - f y = 0 \<longrightarrow> x - y = 0)"
```
```    61     by simp
```
```    62   also have "\<dots> \<longleftrightarrow> (\<forall>x \<in> S. \<forall>y \<in> S. f (x - y) = 0 \<longrightarrow> x - y = 0)"
```
```    63     by (simp add: linear_diff[OF lf])
```
```    64   also have "\<dots> \<longleftrightarrow> (\<forall>x \<in> S. f x = 0 \<longrightarrow> x = 0)"
```
```    65     using \<open>subspace S\<close> subspace_def[of S] subspace_diff[of S] by auto
```
```    66   finally show ?thesis .
```
```    67 qed
```
```    68
```
```    69 lemma subspace_Inter: "\<forall>s \<in> f. subspace s \<Longrightarrow> subspace (\<Inter>f)"
```
```    70   unfolding subspace_def by auto
```
```    71
```
```    72 lemma span_eq[simp]: "span s = s \<longleftrightarrow> subspace s"
```
```    73   unfolding span_def by (rule hull_eq) (rule subspace_Inter)
```
```    74
```
```    75 lemma substdbasis_expansion_unique:
```
```    76   assumes d: "d \<subseteq> Basis"
```
```    77   shows "(\<Sum>i\<in>d. f i *\<^sub>R i) = (x::'a::euclidean_space) \<longleftrightarrow>
```
```    78     (\<forall>i\<in>Basis. (i \<in> d \<longrightarrow> f i = x \<bullet> i) \<and> (i \<notin> d \<longrightarrow> x \<bullet> i = 0))"
```
```    79 proof -
```
```    80   have *: "\<And>x a b P. x * (if P then a else b) = (if P then x * a else x * b)"
```
```    81     by auto
```
```    82   have **: "finite d"
```
```    83     by (auto intro: finite_subset[OF assms])
```
```    84   have ***: "\<And>i. i \<in> Basis \<Longrightarrow> (\<Sum>i\<in>d. f i *\<^sub>R i) \<bullet> i = (\<Sum>x\<in>d. if x = i then f x else 0)"
```
```    85     using d
```
```    86     by (auto intro!: sum.cong simp: inner_Basis inner_sum_left)
```
```    87   show ?thesis
```
```    88     unfolding euclidean_eq_iff[where 'a='a] by (auto simp: sum.delta[OF **] ***)
```
```    89 qed
```
```    90
```
```    91 lemma independent_substdbasis: "d \<subseteq> Basis \<Longrightarrow> independent d"
```
```    92   by (rule independent_mono[OF independent_Basis])
```
```    93
```
```    94 lemma dim_cball:
```
```    95   assumes "e > 0"
```
```    96   shows "dim (cball (0 :: 'n::euclidean_space) e) = DIM('n)"
```
```    97 proof -
```
```    98   {
```
```    99     fix x :: "'n::euclidean_space"
```
```   100     define y where "y = (e / norm x) *\<^sub>R x"
```
```   101     then have "y \<in> cball 0 e"
```
```   102       using assms by auto
```
```   103     moreover have *: "x = (norm x / e) *\<^sub>R y"
```
```   104       using y_def assms by simp
```
```   105     moreover from * have "x = (norm x/e) *\<^sub>R y"
```
```   106       by auto
```
```   107     ultimately have "x \<in> span (cball 0 e)"
```
```   108       using span_mul[of y "cball 0 e" "norm x/e"] span_inc[of "cball 0 e"]
```
```   109       by (simp add: span_superset)
```
```   110   }
```
```   111   then have "span (cball 0 e) = (UNIV :: 'n::euclidean_space set)"
```
```   112     by auto
```
```   113   then show ?thesis
```
```   114     using dim_span[of "cball (0 :: 'n::euclidean_space) e"] by (auto simp add: dim_UNIV)
```
```   115 qed
```
```   116
```
```   117 lemma indep_card_eq_dim_span:
```
```   118   fixes B :: "'n::euclidean_space set"
```
```   119   assumes "independent B"
```
```   120   shows "finite B \<and> card B = dim (span B)"
```
```   121   using assms basis_card_eq_dim[of B "span B"] span_inc by auto
```
```   122
```
```   123 lemma sum_not_0: "sum f A \<noteq> 0 \<Longrightarrow> \<exists>a \<in> A. f a \<noteq> 0"
```
```   124   by (rule ccontr) auto
```
```   125
```
```   126 lemma subset_translation_eq [simp]:
```
```   127     fixes a :: "'a::real_vector" shows "(+) a ` s \<subseteq> (+) a ` t \<longleftrightarrow> s \<subseteq> t"
```
```   128   by auto
```
```   129
```
```   130 lemma translate_inj_on:
```
```   131   fixes A :: "'a::ab_group_add set"
```
```   132   shows "inj_on (\<lambda>x. a + x) A"
```
```   133   unfolding inj_on_def by auto
```
```   134
```
```   135 lemma translation_assoc:
```
```   136   fixes a b :: "'a::ab_group_add"
```
```   137   shows "(\<lambda>x. b + x) ` ((\<lambda>x. a + x) ` S) = (\<lambda>x. (a + b) + x) ` S"
```
```   138   by auto
```
```   139
```
```   140 lemma translation_invert:
```
```   141   fixes a :: "'a::ab_group_add"
```
```   142   assumes "(\<lambda>x. a + x) ` A = (\<lambda>x. a + x) ` B"
```
```   143   shows "A = B"
```
```   144 proof -
```
```   145   have "(\<lambda>x. -a + x) ` ((\<lambda>x. a + x) ` A) = (\<lambda>x. - a + x) ` ((\<lambda>x. a + x) ` B)"
```
```   146     using assms by auto
```
```   147   then show ?thesis
```
```   148     using translation_assoc[of "-a" a A] translation_assoc[of "-a" a B] by auto
```
```   149 qed
```
```   150
```
```   151 lemma translation_galois:
```
```   152   fixes a :: "'a::ab_group_add"
```
```   153   shows "T = ((\<lambda>x. a + x) ` S) \<longleftrightarrow> S = ((\<lambda>x. (- a) + x) ` T)"
```
```   154   using translation_assoc[of "-a" a S]
```
```   155   apply auto
```
```   156   using translation_assoc[of a "-a" T]
```
```   157   apply auto
```
```   158   done
```
```   159
```
```   160 lemma translation_inverse_subset:
```
```   161   assumes "((\<lambda>x. - a + x) ` V) \<le> (S :: 'n::ab_group_add set)"
```
```   162   shows "V \<le> ((\<lambda>x. a + x) ` S)"
```
```   163 proof -
```
```   164   {
```
```   165     fix x
```
```   166     assume "x \<in> V"
```
```   167     then have "x-a \<in> S" using assms by auto
```
```   168     then have "x \<in> {a + v |v. v \<in> S}"
```
```   169       apply auto
```
```   170       apply (rule exI[of _ "x-a"])
```
```   171       apply simp
```
```   172       done
```
```   173     then have "x \<in> ((\<lambda>x. a+x) ` S)" by auto
```
```   174   }
```
```   175   then show ?thesis by auto
```
```   176 qed
```
```   177
```
```   178 subsection \<open>Convexity\<close>
```
```   179
```
```   180 definition%important convex :: "'a::real_vector set \<Rightarrow> bool"
```
```   181   where "convex s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u\<ge>0. \<forall>v\<ge>0. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> s)"
```
```   182
```
```   183 lemma convexI:
```
```   184   assumes "\<And>x y u v. x \<in> s \<Longrightarrow> y \<in> s \<Longrightarrow> 0 \<le> u \<Longrightarrow> 0 \<le> v \<Longrightarrow> u + v = 1 \<Longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> s"
```
```   185   shows "convex s"
```
```   186   using assms unfolding convex_def by fast
```
```   187
```
```   188 lemma convexD:
```
```   189   assumes "convex s" and "x \<in> s" and "y \<in> s" and "0 \<le> u" and "0 \<le> v" and "u + v = 1"
```
```   190   shows "u *\<^sub>R x + v *\<^sub>R y \<in> s"
```
```   191   using assms unfolding convex_def by fast
```
```   192
```
```   193 lemma convex_alt: "convex s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u. 0 \<le> u \<and> u \<le> 1 \<longrightarrow> ((1 - u) *\<^sub>R x + u *\<^sub>R y) \<in> s)"
```
```   194   (is "_ \<longleftrightarrow> ?alt")
```
```   195 proof
```
```   196   show "convex s" if alt: ?alt
```
```   197   proof -
```
```   198     {
```
```   199       fix x y and u v :: real
```
```   200       assume mem: "x \<in> s" "y \<in> s"
```
```   201       assume "0 \<le> u" "0 \<le> v"
```
```   202       moreover
```
```   203       assume "u + v = 1"
```
```   204       then have "u = 1 - v" by auto
```
```   205       ultimately have "u *\<^sub>R x + v *\<^sub>R y \<in> s"
```
```   206         using alt [rule_format, OF mem] by auto
```
```   207     }
```
```   208     then show ?thesis
```
```   209       unfolding convex_def by auto
```
```   210   qed
```
```   211   show ?alt if "convex s"
```
```   212     using that by (auto simp: convex_def)
```
```   213 qed
```
```   214
```
```   215 lemma convexD_alt:
```
```   216   assumes "convex s" "a \<in> s" "b \<in> s" "0 \<le> u" "u \<le> 1"
```
```   217   shows "((1 - u) *\<^sub>R a + u *\<^sub>R b) \<in> s"
```
```   218   using assms unfolding convex_alt by auto
```
```   219
```
```   220 lemma mem_convex_alt:
```
```   221   assumes "convex S" "x \<in> S" "y \<in> S" "u \<ge> 0" "v \<ge> 0" "u + v > 0"
```
```   222   shows "((u/(u+v)) *\<^sub>R x + (v/(u+v)) *\<^sub>R y) \<in> S"
```
```   223   apply (rule convexD)
```
```   224   using assms
```
```   225        apply (simp_all add: zero_le_divide_iff add_divide_distrib [symmetric])
```
```   226   done
```
```   227
```
```   228 lemma convex_empty[intro,simp]: "convex {}"
```
```   229   unfolding convex_def by simp
```
```   230
```
```   231 lemma convex_singleton[intro,simp]: "convex {a}"
```
```   232   unfolding convex_def by (auto simp: scaleR_left_distrib[symmetric])
```
```   233
```
```   234 lemma convex_UNIV[intro,simp]: "convex UNIV"
```
```   235   unfolding convex_def by auto
```
```   236
```
```   237 lemma convex_Inter: "(\<And>s. s\<in>f \<Longrightarrow> convex s) \<Longrightarrow> convex(\<Inter>f)"
```
```   238   unfolding convex_def by auto
```
```   239
```
```   240 lemma convex_Int: "convex s \<Longrightarrow> convex t \<Longrightarrow> convex (s \<inter> t)"
```
```   241   unfolding convex_def by auto
```
```   242
```
```   243 lemma convex_INT: "(\<And>i. i \<in> A \<Longrightarrow> convex (B i)) \<Longrightarrow> convex (\<Inter>i\<in>A. B i)"
```
```   244   unfolding convex_def by auto
```
```   245
```
```   246 lemma convex_Times: "convex s \<Longrightarrow> convex t \<Longrightarrow> convex (s \<times> t)"
```
```   247   unfolding convex_def by auto
```
```   248
```
```   249 lemma convex_halfspace_le: "convex {x. inner a x \<le> b}"
```
```   250   unfolding convex_def
```
```   251   by (auto simp: inner_add intro!: convex_bound_le)
```
```   252
```
```   253 lemma convex_halfspace_ge: "convex {x. inner a x \<ge> b}"
```
```   254 proof -
```
```   255   have *: "{x. inner a x \<ge> b} = {x. inner (-a) x \<le> -b}"
```
```   256     by auto
```
```   257   show ?thesis
```
```   258     unfolding * using convex_halfspace_le[of "-a" "-b"] by auto
```
```   259 qed
```
```   260
```
```   261 lemma convex_halfspace_abs_le: "convex {x. \<bar>inner a x\<bar> \<le> b}"
```
```   262 proof -
```
```   263   have *: "{x. \<bar>inner a x\<bar> \<le> b} = {x. inner a x \<le> b} \<inter> {x. -b \<le> inner a x}"
```
```   264     by auto
```
```   265   show ?thesis
```
```   266     unfolding * by (simp add: convex_Int convex_halfspace_ge convex_halfspace_le)
```
```   267 qed
```
```   268
```
```   269 lemma convex_hyperplane: "convex {x. inner a x = b}"
```
```   270 proof -
```
```   271   have *: "{x. inner a x = b} = {x. inner a x \<le> b} \<inter> {x. inner a x \<ge> b}"
```
```   272     by auto
```
```   273   show ?thesis using convex_halfspace_le convex_halfspace_ge
```
```   274     by (auto intro!: convex_Int simp: *)
```
```   275 qed
```
```   276
```
```   277 lemma convex_halfspace_lt: "convex {x. inner a x < b}"
```
```   278   unfolding convex_def
```
```   279   by (auto simp: convex_bound_lt inner_add)
```
```   280
```
```   281 lemma convex_halfspace_gt: "convex {x. inner a x > b}"
```
```   282   using convex_halfspace_lt[of "-a" "-b"] by auto
```
```   283
```
```   284 lemma convex_halfspace_Re_ge: "convex {x. Re x \<ge> b}"
```
```   285   using convex_halfspace_ge[of b "1::complex"] by simp
```
```   286
```
```   287 lemma convex_halfspace_Re_le: "convex {x. Re x \<le> b}"
```
```   288   using convex_halfspace_le[of "1::complex" b] by simp
```
```   289
```
```   290 lemma convex_halfspace_Im_ge: "convex {x. Im x \<ge> b}"
```
```   291   using convex_halfspace_ge[of b \<i>] by simp
```
```   292
```
```   293 lemma convex_halfspace_Im_le: "convex {x. Im x \<le> b}"
```
```   294   using convex_halfspace_le[of \<i> b] by simp
```
```   295
```
```   296 lemma convex_halfspace_Re_gt: "convex {x. Re x > b}"
```
```   297   using convex_halfspace_gt[of b "1::complex"] by simp
```
```   298
```
```   299 lemma convex_halfspace_Re_lt: "convex {x. Re x < b}"
```
```   300   using convex_halfspace_lt[of "1::complex" b] by simp
```
```   301
```
```   302 lemma convex_halfspace_Im_gt: "convex {x. Im x > b}"
```
```   303   using convex_halfspace_gt[of b \<i>] by simp
```
```   304
```
```   305 lemma convex_halfspace_Im_lt: "convex {x. Im x < b}"
```
```   306   using convex_halfspace_lt[of \<i> b] by simp
```
```   307
```
```   308 lemma convex_real_interval [iff]:
```
```   309   fixes a b :: "real"
```
```   310   shows "convex {a..}" and "convex {..b}"
```
```   311     and "convex {a<..}" and "convex {..<b}"
```
```   312     and "convex {a..b}" and "convex {a<..b}"
```
```   313     and "convex {a..<b}" and "convex {a<..<b}"
```
```   314 proof -
```
```   315   have "{a..} = {x. a \<le> inner 1 x}"
```
```   316     by auto
```
```   317   then show 1: "convex {a..}"
```
```   318     by (simp only: convex_halfspace_ge)
```
```   319   have "{..b} = {x. inner 1 x \<le> b}"
```
```   320     by auto
```
```   321   then show 2: "convex {..b}"
```
```   322     by (simp only: convex_halfspace_le)
```
```   323   have "{a<..} = {x. a < inner 1 x}"
```
```   324     by auto
```
```   325   then show 3: "convex {a<..}"
```
```   326     by (simp only: convex_halfspace_gt)
```
```   327   have "{..<b} = {x. inner 1 x < b}"
```
```   328     by auto
```
```   329   then show 4: "convex {..<b}"
```
```   330     by (simp only: convex_halfspace_lt)
```
```   331   have "{a..b} = {a..} \<inter> {..b}"
```
```   332     by auto
```
```   333   then show "convex {a..b}"
```
```   334     by (simp only: convex_Int 1 2)
```
```   335   have "{a<..b} = {a<..} \<inter> {..b}"
```
```   336     by auto
```
```   337   then show "convex {a<..b}"
```
```   338     by (simp only: convex_Int 3 2)
```
```   339   have "{a..<b} = {a..} \<inter> {..<b}"
```
```   340     by auto
```
```   341   then show "convex {a..<b}"
```
```   342     by (simp only: convex_Int 1 4)
```
```   343   have "{a<..<b} = {a<..} \<inter> {..<b}"
```
```   344     by auto
```
```   345   then show "convex {a<..<b}"
```
```   346     by (simp only: convex_Int 3 4)
```
```   347 qed
```
```   348
```
```   349 lemma convex_Reals: "convex \<real>"
```
```   350   by (simp add: convex_def scaleR_conv_of_real)
```
```   351
```
```   352
```
```   353 subsection%unimportant \<open>Explicit expressions for convexity in terms of arbitrary sums\<close>
```
```   354
```
```   355 lemma convex_sum:
```
```   356   fixes C :: "'a::real_vector set"
```
```   357   assumes "finite s"
```
```   358     and "convex C"
```
```   359     and "(\<Sum> i \<in> s. a i) = 1"
```
```   360   assumes "\<And>i. i \<in> s \<Longrightarrow> a i \<ge> 0"
```
```   361     and "\<And>i. i \<in> s \<Longrightarrow> y i \<in> C"
```
```   362   shows "(\<Sum> j \<in> s. a j *\<^sub>R y j) \<in> C"
```
```   363   using assms(1,3,4,5)
```
```   364 proof (induct arbitrary: a set: finite)
```
```   365   case empty
```
```   366   then show ?case by simp
```
```   367 next
```
```   368   case (insert i s) note IH = this(3)
```
```   369   have "a i + sum a s = 1"
```
```   370     and "0 \<le> a i"
```
```   371     and "\<forall>j\<in>s. 0 \<le> a j"
```
```   372     and "y i \<in> C"
```
```   373     and "\<forall>j\<in>s. y j \<in> C"
```
```   374     using insert.hyps(1,2) insert.prems by simp_all
```
```   375   then have "0 \<le> sum a s"
```
```   376     by (simp add: sum_nonneg)
```
```   377   have "a i *\<^sub>R y i + (\<Sum>j\<in>s. a j *\<^sub>R y j) \<in> C"
```
```   378   proof (cases "sum a s = 0")
```
```   379     case True
```
```   380     with \<open>a i + sum a s = 1\<close> have "a i = 1"
```
```   381       by simp
```
```   382     from sum_nonneg_0 [OF \<open>finite s\<close> _ True] \<open>\<forall>j\<in>s. 0 \<le> a j\<close> have "\<forall>j\<in>s. a j = 0"
```
```   383       by simp
```
```   384     show ?thesis using \<open>a i = 1\<close> and \<open>\<forall>j\<in>s. a j = 0\<close> and \<open>y i \<in> C\<close>
```
```   385       by simp
```
```   386   next
```
```   387     case False
```
```   388     with \<open>0 \<le> sum a s\<close> have "0 < sum a s"
```
```   389       by simp
```
```   390     then have "(\<Sum>j\<in>s. (a j / sum a s) *\<^sub>R y j) \<in> C"
```
```   391       using \<open>\<forall>j\<in>s. 0 \<le> a j\<close> and \<open>\<forall>j\<in>s. y j \<in> C\<close>
```
```   392       by (simp add: IH sum_divide_distrib [symmetric])
```
```   393     from \<open>convex C\<close> and \<open>y i \<in> C\<close> and this and \<open>0 \<le> a i\<close>
```
```   394       and \<open>0 \<le> sum a s\<close> and \<open>a i + sum a s = 1\<close>
```
```   395     have "a i *\<^sub>R y i + sum a s *\<^sub>R (\<Sum>j\<in>s. (a j / sum a s) *\<^sub>R y j) \<in> C"
```
```   396       by (rule convexD)
```
```   397     then show ?thesis
```
```   398       by (simp add: scaleR_sum_right False)
```
```   399   qed
```
```   400   then show ?case using \<open>finite s\<close> and \<open>i \<notin> s\<close>
```
```   401     by simp
```
```   402 qed
```
```   403
```
```   404 lemma convex:
```
```   405   "convex s \<longleftrightarrow> (\<forall>(k::nat) u x. (\<forall>i. 1\<le>i \<and> i\<le>k \<longrightarrow> 0 \<le> u i \<and> x i \<in>s) \<and> (sum u {1..k} = 1)
```
```   406       \<longrightarrow> sum (\<lambda>i. u i *\<^sub>R x i) {1..k} \<in> s)"
```
```   407 proof safe
```
```   408   fix k :: nat
```
```   409   fix u :: "nat \<Rightarrow> real"
```
```   410   fix x
```
```   411   assume "convex s"
```
```   412     "\<forall>i. 1 \<le> i \<and> i \<le> k \<longrightarrow> 0 \<le> u i \<and> x i \<in> s"
```
```   413     "sum u {1..k} = 1"
```
```   414   with convex_sum[of "{1 .. k}" s] show "(\<Sum>j\<in>{1 .. k}. u j *\<^sub>R x j) \<in> s"
```
```   415     by auto
```
```   416 next
```
```   417   assume *: "\<forall>k u x. (\<forall> i :: nat. 1 \<le> i \<and> i \<le> k \<longrightarrow> 0 \<le> u i \<and> x i \<in> s) \<and> sum u {1..k} = 1
```
```   418     \<longrightarrow> (\<Sum>i = 1..k. u i *\<^sub>R (x i :: 'a)) \<in> s"
```
```   419   {
```
```   420     fix \<mu> :: real
```
```   421     fix x y :: 'a
```
```   422     assume xy: "x \<in> s" "y \<in> s"
```
```   423     assume mu: "\<mu> \<ge> 0" "\<mu> \<le> 1"
```
```   424     let ?u = "\<lambda>i. if (i :: nat) = 1 then \<mu> else 1 - \<mu>"
```
```   425     let ?x = "\<lambda>i. if (i :: nat) = 1 then x else y"
```
```   426     have "{1 :: nat .. 2} \<inter> - {x. x = 1} = {2}"
```
```   427       by auto
```
```   428     then have card: "card ({1 :: nat .. 2} \<inter> - {x. x = 1}) = 1"
```
```   429       by simp
```
```   430     then have "sum ?u {1 .. 2} = 1"
```
```   431       using sum.If_cases[of "{(1 :: nat) .. 2}" "\<lambda> x. x = 1" "\<lambda> x. \<mu>" "\<lambda> x. 1 - \<mu>"]
```
```   432       by auto
```
```   433     with *[rule_format, of "2" ?u ?x] have s: "(\<Sum>j \<in> {1..2}. ?u j *\<^sub>R ?x j) \<in> s"
```
```   434       using mu xy by auto
```
```   435     have grarr: "(\<Sum>j \<in> {Suc (Suc 0)..2}. ?u j *\<^sub>R ?x j) = (1 - \<mu>) *\<^sub>R y"
```
```   436       using sum_head_Suc[of "Suc (Suc 0)" 2 "\<lambda> j. (1 - \<mu>) *\<^sub>R y"] by auto
```
```   437     from sum_head_Suc[of "Suc 0" 2 "\<lambda> j. ?u j *\<^sub>R ?x j", simplified this]
```
```   438     have "(\<Sum>j \<in> {1..2}. ?u j *\<^sub>R ?x j) = \<mu> *\<^sub>R x + (1 - \<mu>) *\<^sub>R y"
```
```   439       by auto
```
```   440     then have "(1 - \<mu>) *\<^sub>R y + \<mu> *\<^sub>R x \<in> s"
```
```   441       using s by (auto simp: add.commute)
```
```   442   }
```
```   443   then show "convex s"
```
```   444     unfolding convex_alt by auto
```
```   445 qed
```
```   446
```
```   447
```
```   448 lemma convex_explicit:
```
```   449   fixes s :: "'a::real_vector set"
```
```   450   shows "convex s \<longleftrightarrow>
```
```   451     (\<forall>t u. finite t \<and> t \<subseteq> s \<and> (\<forall>x\<in>t. 0 \<le> u x) \<and> sum u t = 1 \<longrightarrow> sum (\<lambda>x. u x *\<^sub>R x) t \<in> s)"
```
```   452 proof safe
```
```   453   fix t
```
```   454   fix u :: "'a \<Rightarrow> real"
```
```   455   assume "convex s"
```
```   456     and "finite t"
```
```   457     and "t \<subseteq> s" "\<forall>x\<in>t. 0 \<le> u x" "sum u t = 1"
```
```   458   then show "(\<Sum>x\<in>t. u x *\<^sub>R x) \<in> s"
```
```   459     using convex_sum[of t s u "\<lambda> x. x"] by auto
```
```   460 next
```
```   461   assume *: "\<forall>t. \<forall> u. finite t \<and> t \<subseteq> s \<and> (\<forall>x\<in>t. 0 \<le> u x) \<and>
```
```   462     sum u t = 1 \<longrightarrow> (\<Sum>x\<in>t. u x *\<^sub>R x) \<in> s"
```
```   463   show "convex s"
```
```   464     unfolding convex_alt
```
```   465   proof safe
```
```   466     fix x y
```
```   467     fix \<mu> :: real
```
```   468     assume **: "x \<in> s" "y \<in> s" "0 \<le> \<mu>" "\<mu> \<le> 1"
```
```   469     show "(1 - \<mu>) *\<^sub>R x + \<mu> *\<^sub>R y \<in> s"
```
```   470     proof (cases "x = y")
```
```   471       case False
```
```   472       then show ?thesis
```
```   473         using *[rule_format, of "{x, y}" "\<lambda> z. if z = x then 1 - \<mu> else \<mu>"] **
```
```   474         by auto
```
```   475     next
```
```   476       case True
```
```   477       then show ?thesis
```
```   478         using *[rule_format, of "{x, y}" "\<lambda> z. 1"] **
```
```   479         by (auto simp: field_simps real_vector.scale_left_diff_distrib)
```
```   480     qed
```
```   481   qed
```
```   482 qed
```
```   483
```
```   484 lemma convex_finite:
```
```   485   assumes "finite s"
```
```   486   shows "convex s \<longleftrightarrow> (\<forall>u. (\<forall>x\<in>s. 0 \<le> u x) \<and> sum u s = 1 \<longrightarrow> sum (\<lambda>x. u x *\<^sub>R x) s \<in> s)"
```
```   487   unfolding convex_explicit
```
```   488   apply safe
```
```   489   subgoal for u by (erule allE [where x=s], erule allE [where x=u]) auto
```
```   490   subgoal for t u
```
```   491   proof -
```
```   492     have if_distrib_arg: "\<And>P f g x. (if P then f else g) x = (if P then f x else g x)"
```
```   493       by simp
```
```   494     assume sum: "\<forall>u. (\<forall>x\<in>s. 0 \<le> u x) \<and> sum u s = 1 \<longrightarrow> (\<Sum>x\<in>s. u x *\<^sub>R x) \<in> s"
```
```   495     assume *: "\<forall>x\<in>t. 0 \<le> u x" "sum u t = 1"
```
```   496     assume "t \<subseteq> s"
```
```   497     then have "s \<inter> t = t" by auto
```
```   498     with sum[THEN spec[where x="\<lambda>x. if x\<in>t then u x else 0"]] * show "(\<Sum>x\<in>t. u x *\<^sub>R x) \<in> s"
```
```   499       by (auto simp: assms sum.If_cases if_distrib if_distrib_arg)
```
```   500   qed
```
```   501   done
```
```   502
```
```   503
```
```   504 subsection \<open>Functions that are convex on a set\<close>
```
```   505
```
```   506 definition%important convex_on :: "'a::real_vector set \<Rightarrow> ('a \<Rightarrow> real) \<Rightarrow> bool"
```
```   507   where "convex_on s f \<longleftrightarrow>
```
```   508     (\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u\<ge>0. \<forall>v\<ge>0. u + v = 1 \<longrightarrow> f (u *\<^sub>R x + v *\<^sub>R y) \<le> u * f x + v * f y)"
```
```   509
```
```   510 lemma convex_onI [intro?]:
```
```   511   assumes "\<And>t x y. t > 0 \<Longrightarrow> t < 1 \<Longrightarrow> x \<in> A \<Longrightarrow> y \<in> A \<Longrightarrow>
```
```   512     f ((1 - t) *\<^sub>R x + t *\<^sub>R y) \<le> (1 - t) * f x + t * f y"
```
```   513   shows "convex_on A f"
```
```   514   unfolding convex_on_def
```
```   515 proof clarify
```
```   516   fix x y
```
```   517   fix u v :: real
```
```   518   assume A: "x \<in> A" "y \<in> A" "u \<ge> 0" "v \<ge> 0" "u + v = 1"
```
```   519   from A(5) have [simp]: "v = 1 - u"
```
```   520     by (simp add: algebra_simps)
```
```   521   from A(1-4) show "f (u *\<^sub>R x + v *\<^sub>R y) \<le> u * f x + v * f y"
```
```   522     using assms[of u y x]
```
```   523     by (cases "u = 0 \<or> u = 1") (auto simp: algebra_simps)
```
```   524 qed
```
```   525
```
```   526 lemma convex_on_linorderI [intro?]:
```
```   527   fixes A :: "('a::{linorder,real_vector}) set"
```
```   528   assumes "\<And>t x y. t > 0 \<Longrightarrow> t < 1 \<Longrightarrow> x \<in> A \<Longrightarrow> y \<in> A \<Longrightarrow> x < y \<Longrightarrow>
```
```   529     f ((1 - t) *\<^sub>R x + t *\<^sub>R y) \<le> (1 - t) * f x + t * f y"
```
```   530   shows "convex_on A f"
```
```   531 proof
```
```   532   fix x y
```
```   533   fix t :: real
```
```   534   assume A: "x \<in> A" "y \<in> A" "t > 0" "t < 1"
```
```   535   with assms [of t x y] assms [of "1 - t" y x]
```
```   536   show "f ((1 - t) *\<^sub>R x + t *\<^sub>R y) \<le> (1 - t) * f x + t * f y"
```
```   537     by (cases x y rule: linorder_cases) (auto simp: algebra_simps)
```
```   538 qed
```
```   539
```
```   540 lemma convex_onD:
```
```   541   assumes "convex_on A f"
```
```   542   shows "\<And>t x y. t \<ge> 0 \<Longrightarrow> t \<le> 1 \<Longrightarrow> x \<in> A \<Longrightarrow> y \<in> A \<Longrightarrow>
```
```   543     f ((1 - t) *\<^sub>R x + t *\<^sub>R y) \<le> (1 - t) * f x + t * f y"
```
```   544   using assms by (auto simp: convex_on_def)
```
```   545
```
```   546 lemma convex_onD_Icc:
```
```   547   assumes "convex_on {x..y} f" "x \<le> (y :: _ :: {real_vector,preorder})"
```
```   548   shows "\<And>t. t \<ge> 0 \<Longrightarrow> t \<le> 1 \<Longrightarrow>
```
```   549     f ((1 - t) *\<^sub>R x + t *\<^sub>R y) \<le> (1 - t) * f x + t * f y"
```
```   550   using assms(2) by (intro convex_onD [OF assms(1)]) simp_all
```
```   551
```
```   552 lemma convex_on_subset: "convex_on t f \<Longrightarrow> s \<subseteq> t \<Longrightarrow> convex_on s f"
```
```   553   unfolding convex_on_def by auto
```
```   554
```
```   555 lemma convex_on_add [intro]:
```
```   556   assumes "convex_on s f"
```
```   557     and "convex_on s g"
```
```   558   shows "convex_on s (\<lambda>x. f x + g x)"
```
```   559 proof -
```
```   560   {
```
```   561     fix x y
```
```   562     assume "x \<in> s" "y \<in> s"
```
```   563     moreover
```
```   564     fix u v :: real
```
```   565     assume "0 \<le> u" "0 \<le> v" "u + v = 1"
```
```   566     ultimately
```
```   567     have "f (u *\<^sub>R x + v *\<^sub>R y) + g (u *\<^sub>R x + v *\<^sub>R y) \<le> (u * f x + v * f y) + (u * g x + v * g y)"
```
```   568       using assms unfolding convex_on_def by (auto simp: add_mono)
```
```   569     then have "f (u *\<^sub>R x + v *\<^sub>R y) + g (u *\<^sub>R x + v *\<^sub>R y) \<le> u * (f x + g x) + v * (f y + g y)"
```
```   570       by (simp add: field_simps)
```
```   571   }
```
```   572   then show ?thesis
```
```   573     unfolding convex_on_def by auto
```
```   574 qed
```
```   575
```
```   576 lemma convex_on_cmul [intro]:
```
```   577   fixes c :: real
```
```   578   assumes "0 \<le> c"
```
```   579     and "convex_on s f"
```
```   580   shows "convex_on s (\<lambda>x. c * f x)"
```
```   581 proof -
```
```   582   have *: "u * (c * fx) + v * (c * fy) = c * (u * fx + v * fy)"
```
```   583     for u c fx v fy :: real
```
```   584     by (simp add: field_simps)
```
```   585   show ?thesis using assms(2) and mult_left_mono [OF _ assms(1)]
```
```   586     unfolding convex_on_def and * by auto
```
```   587 qed
```
```   588
```
```   589 lemma convex_lower:
```
```   590   assumes "convex_on s f"
```
```   591     and "x \<in> s"
```
```   592     and "y \<in> s"
```
```   593     and "0 \<le> u"
```
```   594     and "0 \<le> v"
```
```   595     and "u + v = 1"
```
```   596   shows "f (u *\<^sub>R x + v *\<^sub>R y) \<le> max (f x) (f y)"
```
```   597 proof -
```
```   598   let ?m = "max (f x) (f y)"
```
```   599   have "u * f x + v * f y \<le> u * max (f x) (f y) + v * max (f x) (f y)"
```
```   600     using assms(4,5) by (auto simp: mult_left_mono add_mono)
```
```   601   also have "\<dots> = max (f x) (f y)"
```
```   602     using assms(6) by (simp add: distrib_right [symmetric])
```
```   603   finally show ?thesis
```
```   604     using assms unfolding convex_on_def by fastforce
```
```   605 qed
```
```   606
```
```   607 lemma convex_on_dist [intro]:
```
```   608   fixes s :: "'a::real_normed_vector set"
```
```   609   shows "convex_on s (\<lambda>x. dist a x)"
```
```   610 proof (auto simp: convex_on_def dist_norm)
```
```   611   fix x y
```
```   612   assume "x \<in> s" "y \<in> s"
```
```   613   fix u v :: real
```
```   614   assume "0 \<le> u"
```
```   615   assume "0 \<le> v"
```
```   616   assume "u + v = 1"
```
```   617   have "a = u *\<^sub>R a + v *\<^sub>R a"
```
```   618     unfolding scaleR_left_distrib[symmetric] and \<open>u + v = 1\<close> by simp
```
```   619   then have *: "a - (u *\<^sub>R x + v *\<^sub>R y) = (u *\<^sub>R (a - x)) + (v *\<^sub>R (a - y))"
```
```   620     by (auto simp: algebra_simps)
```
```   621   show "norm (a - (u *\<^sub>R x + v *\<^sub>R y)) \<le> u * norm (a - x) + v * norm (a - y)"
```
```   622     unfolding * using norm_triangle_ineq[of "u *\<^sub>R (a - x)" "v *\<^sub>R (a - y)"]
```
```   623     using \<open>0 \<le> u\<close> \<open>0 \<le> v\<close> by auto
```
```   624 qed
```
```   625
```
```   626
```
```   627 subsection%unimportant \<open>Arithmetic operations on sets preserve convexity\<close>
```
```   628
```
```   629 lemma convex_linear_image:
```
```   630   assumes "linear f"
```
```   631     and "convex s"
```
```   632   shows "convex (f ` s)"
```
```   633 proof -
```
```   634   interpret f: linear f by fact
```
```   635   from \<open>convex s\<close> show "convex (f ` s)"
```
```   636     by (simp add: convex_def f.scaleR [symmetric] f.add [symmetric])
```
```   637 qed
```
```   638
```
```   639 lemma convex_linear_vimage:
```
```   640   assumes "linear f"
```
```   641     and "convex s"
```
```   642   shows "convex (f -` s)"
```
```   643 proof -
```
```   644   interpret f: linear f by fact
```
```   645   from \<open>convex s\<close> show "convex (f -` s)"
```
```   646     by (simp add: convex_def f.add f.scaleR)
```
```   647 qed
```
```   648
```
```   649 lemma convex_scaling:
```
```   650   assumes "convex s"
```
```   651   shows "convex ((\<lambda>x. c *\<^sub>R x) ` s)"
```
```   652 proof -
```
```   653   have "linear (\<lambda>x. c *\<^sub>R x)"
```
```   654     by (simp add: linearI scaleR_add_right)
```
```   655   then show ?thesis
```
```   656     using \<open>convex s\<close> by (rule convex_linear_image)
```
```   657 qed
```
```   658
```
```   659 lemma convex_scaled:
```
```   660   assumes "convex S"
```
```   661   shows "convex ((\<lambda>x. x *\<^sub>R c) ` S)"
```
```   662 proof -
```
```   663   have "linear (\<lambda>x. x *\<^sub>R c)"
```
```   664     by (simp add: linearI scaleR_add_left)
```
```   665   then show ?thesis
```
```   666     using \<open>convex S\<close> by (rule convex_linear_image)
```
```   667 qed
```
```   668
```
```   669 lemma convex_negations:
```
```   670   assumes "convex S"
```
```   671   shows "convex ((\<lambda>x. - x) ` S)"
```
```   672 proof -
```
```   673   have "linear (\<lambda>x. - x)"
```
```   674     by (simp add: linearI)
```
```   675   then show ?thesis
```
```   676     using \<open>convex S\<close> by (rule convex_linear_image)
```
```   677 qed
```
```   678
```
```   679 lemma convex_sums:
```
```   680   assumes "convex S"
```
```   681     and "convex T"
```
```   682   shows "convex (\<Union>x\<in> S. \<Union>y \<in> T. {x + y})"
```
```   683 proof -
```
```   684   have "linear (\<lambda>(x, y). x + y)"
```
```   685     by (auto intro: linearI simp: scaleR_add_right)
```
```   686   with assms have "convex ((\<lambda>(x, y). x + y) ` (S \<times> T))"
```
```   687     by (intro convex_linear_image convex_Times)
```
```   688   also have "((\<lambda>(x, y). x + y) ` (S \<times> T)) = (\<Union>x\<in> S. \<Union>y \<in> T. {x + y})"
```
```   689     by auto
```
```   690   finally show ?thesis .
```
```   691 qed
```
```   692
```
```   693 lemma convex_differences:
```
```   694   assumes "convex S" "convex T"
```
```   695   shows "convex (\<Union>x\<in> S. \<Union>y \<in> T. {x - y})"
```
```   696 proof -
```
```   697   have "{x - y| x y. x \<in> S \<and> y \<in> T} = {x + y |x y. x \<in> S \<and> y \<in> uminus ` T}"
```
```   698     by (auto simp: diff_conv_add_uminus simp del: add_uminus_conv_diff)
```
```   699   then show ?thesis
```
```   700     using convex_sums[OF assms(1) convex_negations[OF assms(2)]] by auto
```
```   701 qed
```
```   702
```
```   703 lemma convex_translation:
```
```   704   assumes "convex S"
```
```   705   shows "convex ((\<lambda>x. a + x) ` S)"
```
```   706 proof -
```
```   707   have "(\<Union> x\<in> {a}. \<Union>y \<in> S. {x + y}) = (\<lambda>x. a + x) ` S"
```
```   708     by auto
```
```   709   then show ?thesis
```
```   710     using convex_sums[OF convex_singleton[of a] assms] by auto
```
```   711 qed
```
```   712
```
```   713 lemma convex_affinity:
```
```   714   assumes "convex S"
```
```   715   shows "convex ((\<lambda>x. a + c *\<^sub>R x) ` S)"
```
```   716 proof -
```
```   717   have "(\<lambda>x. a + c *\<^sub>R x) ` S = (+) a ` ( *\<^sub>R) c ` S"
```
```   718     by auto
```
```   719   then show ?thesis
```
```   720     using convex_translation[OF convex_scaling[OF assms], of a c] by auto
```
```   721 qed
```
```   722
```
```   723 lemma pos_is_convex: "convex {0 :: real <..}"
```
```   724   unfolding convex_alt
```
```   725 proof safe
```
```   726   fix y x \<mu> :: real
```
```   727   assume *: "y > 0" "x > 0" "\<mu> \<ge> 0" "\<mu> \<le> 1"
```
```   728   {
```
```   729     assume "\<mu> = 0"
```
```   730     then have "\<mu> *\<^sub>R x + (1 - \<mu>) *\<^sub>R y = y"
```
```   731       by simp
```
```   732     then have "\<mu> *\<^sub>R x + (1 - \<mu>) *\<^sub>R y > 0"
```
```   733       using * by simp
```
```   734   }
```
```   735   moreover
```
```   736   {
```
```   737     assume "\<mu> = 1"
```
```   738     then have "\<mu> *\<^sub>R x + (1 - \<mu>) *\<^sub>R y > 0"
```
```   739       using * by simp
```
```   740   }
```
```   741   moreover
```
```   742   {
```
```   743     assume "\<mu> \<noteq> 1" "\<mu> \<noteq> 0"
```
```   744     then have "\<mu> > 0" "(1 - \<mu>) > 0"
```
```   745       using * by auto
```
```   746     then have "\<mu> *\<^sub>R x + (1 - \<mu>) *\<^sub>R y > 0"
```
```   747       using * by (auto simp: add_pos_pos)
```
```   748   }
```
```   749   ultimately show "(1 - \<mu>) *\<^sub>R y + \<mu> *\<^sub>R x > 0"
```
```   750     by fastforce
```
```   751 qed
```
```   752
```
```   753 lemma convex_on_sum:
```
```   754   fixes a :: "'a \<Rightarrow> real"
```
```   755     and y :: "'a \<Rightarrow> 'b::real_vector"
```
```   756     and f :: "'b \<Rightarrow> real"
```
```   757   assumes "finite s" "s \<noteq> {}"
```
```   758     and "convex_on C f"
```
```   759     and "convex C"
```
```   760     and "(\<Sum> i \<in> s. a i) = 1"
```
```   761     and "\<And>i. i \<in> s \<Longrightarrow> a i \<ge> 0"
```
```   762     and "\<And>i. i \<in> s \<Longrightarrow> y i \<in> C"
```
```   763   shows "f (\<Sum> i \<in> s. a i *\<^sub>R y i) \<le> (\<Sum> i \<in> s. a i * f (y i))"
```
```   764   using assms
```
```   765 proof (induct s arbitrary: a rule: finite_ne_induct)
```
```   766   case (singleton i)
```
```   767   then have ai: "a i = 1"
```
```   768     by auto
```
```   769   then show ?case
```
```   770     by auto
```
```   771 next
```
```   772   case (insert i s)
```
```   773   then have "convex_on C f"
```
```   774     by simp
```
```   775   from this[unfolded convex_on_def, rule_format]
```
```   776   have conv: "\<And>x y \<mu>. x \<in> C \<Longrightarrow> y \<in> C \<Longrightarrow> 0 \<le> \<mu> \<Longrightarrow> \<mu> \<le> 1 \<Longrightarrow>
```
```   777       f (\<mu> *\<^sub>R x + (1 - \<mu>) *\<^sub>R y) \<le> \<mu> * f x + (1 - \<mu>) * f y"
```
```   778     by simp
```
```   779   show ?case
```
```   780   proof (cases "a i = 1")
```
```   781     case True
```
```   782     then have "(\<Sum> j \<in> s. a j) = 0"
```
```   783       using insert by auto
```
```   784     then have "\<And>j. j \<in> s \<Longrightarrow> a j = 0"
```
```   785       using insert by (fastforce simp: sum_nonneg_eq_0_iff)
```
```   786     then show ?thesis
```
```   787       using insert by auto
```
```   788   next
```
```   789     case False
```
```   790     from insert have yai: "y i \<in> C" "a i \<ge> 0"
```
```   791       by auto
```
```   792     have fis: "finite (insert i s)"
```
```   793       using insert by auto
```
```   794     then have ai1: "a i \<le> 1"
```
```   795       using sum_nonneg_leq_bound[of "insert i s" a] insert by simp
```
```   796     then have "a i < 1"
```
```   797       using False by auto
```
```   798     then have i0: "1 - a i > 0"
```
```   799       by auto
```
```   800     let ?a = "\<lambda>j. a j / (1 - a i)"
```
```   801     have a_nonneg: "?a j \<ge> 0" if "j \<in> s" for j
```
```   802       using i0 insert that by fastforce
```
```   803     have "(\<Sum> j \<in> insert i s. a j) = 1"
```
```   804       using insert by auto
```
```   805     then have "(\<Sum> j \<in> s. a j) = 1 - a i"
```
```   806       using sum.insert insert by fastforce
```
```   807     then have "(\<Sum> j \<in> s. a j) / (1 - a i) = 1"
```
```   808       using i0 by auto
```
```   809     then have a1: "(\<Sum> j \<in> s. ?a j) = 1"
```
```   810       unfolding sum_divide_distrib by simp
```
```   811     have "convex C" using insert by auto
```
```   812     then have asum: "(\<Sum> j \<in> s. ?a j *\<^sub>R y j) \<in> C"
```
```   813       using insert convex_sum [OF \<open>finite s\<close> \<open>convex C\<close> a1 a_nonneg] by auto
```
```   814     have asum_le: "f (\<Sum> j \<in> s. ?a j *\<^sub>R y j) \<le> (\<Sum> j \<in> s. ?a j * f (y j))"
```
```   815       using a_nonneg a1 insert by blast
```
```   816     have "f (\<Sum> j \<in> insert i s. a j *\<^sub>R y j) = f ((\<Sum> j \<in> s. a j *\<^sub>R y j) + a i *\<^sub>R y i)"
```
```   817       using sum.insert[of s i "\<lambda> j. a j *\<^sub>R y j", OF \<open>finite s\<close> \<open>i \<notin> s\<close>] insert
```
```   818       by (auto simp only: add.commute)
```
```   819     also have "\<dots> = f (((1 - a i) * inverse (1 - a i)) *\<^sub>R (\<Sum> j \<in> s. a j *\<^sub>R y j) + a i *\<^sub>R y i)"
```
```   820       using i0 by auto
```
```   821     also have "\<dots> = f ((1 - a i) *\<^sub>R (\<Sum> j \<in> s. (a j * inverse (1 - a i)) *\<^sub>R y j) + a i *\<^sub>R y i)"
```
```   822       using scaleR_right.sum[of "inverse (1 - a i)" "\<lambda> j. a j *\<^sub>R y j" s, symmetric]
```
```   823       by (auto simp: algebra_simps)
```
```   824     also have "\<dots> = f ((1 - a i) *\<^sub>R (\<Sum> j \<in> s. ?a j *\<^sub>R y j) + a i *\<^sub>R y i)"
```
```   825       by (auto simp: divide_inverse)
```
```   826     also have "\<dots> \<le> (1 - a i) *\<^sub>R f ((\<Sum> j \<in> s. ?a j *\<^sub>R y j)) + a i * f (y i)"
```
```   827       using conv[of "y i" "(\<Sum> j \<in> s. ?a j *\<^sub>R y j)" "a i", OF yai(1) asum yai(2) ai1]
```
```   828       by (auto simp: add.commute)
```
```   829     also have "\<dots> \<le> (1 - a i) * (\<Sum> j \<in> s. ?a j * f (y j)) + a i * f (y i)"
```
```   830       using add_right_mono [OF mult_left_mono [of _ _ "1 - a i",
```
```   831             OF asum_le less_imp_le[OF i0]], of "a i * f (y i)"]
```
```   832       by simp
```
```   833     also have "\<dots> = (\<Sum> j \<in> s. (1 - a i) * ?a j * f (y j)) + a i * f (y i)"
```
```   834       unfolding sum_distrib_left[of "1 - a i" "\<lambda> j. ?a j * f (y j)"]
```
```   835       using i0 by auto
```
```   836     also have "\<dots> = (\<Sum> j \<in> s. a j * f (y j)) + a i * f (y i)"
```
```   837       using i0 by auto
```
```   838     also have "\<dots> = (\<Sum> j \<in> insert i s. a j * f (y j))"
```
```   839       using insert by auto
```
```   840     finally show ?thesis
```
```   841       by simp
```
```   842   qed
```
```   843 qed
```
```   844
```
```   845 lemma convex_on_alt:
```
```   846   fixes C :: "'a::real_vector set"
```
```   847   assumes "convex C"
```
```   848   shows "convex_on C f \<longleftrightarrow>
```
```   849     (\<forall>x \<in> C. \<forall> y \<in> C. \<forall> \<mu> :: real. \<mu> \<ge> 0 \<and> \<mu> \<le> 1 \<longrightarrow>
```
```   850       f (\<mu> *\<^sub>R x + (1 - \<mu>) *\<^sub>R y) \<le> \<mu> * f x + (1 - \<mu>) * f y)"
```
```   851 proof safe
```
```   852   fix x y
```
```   853   fix \<mu> :: real
```
```   854   assume *: "convex_on C f" "x \<in> C" "y \<in> C" "0 \<le> \<mu>" "\<mu> \<le> 1"
```
```   855   from this[unfolded convex_on_def, rule_format]
```
```   856   have "0 \<le> u \<Longrightarrow> 0 \<le> v \<Longrightarrow> u + v = 1 \<Longrightarrow> f (u *\<^sub>R x + v *\<^sub>R y) \<le> u * f x + v * f y" for u v
```
```   857     by auto
```
```   858   from this [of "\<mu>" "1 - \<mu>", simplified] *
```
```   859   show "f (\<mu> *\<^sub>R x + (1 - \<mu>) *\<^sub>R y) \<le> \<mu> * f x + (1 - \<mu>) * f y"
```
```   860     by auto
```
```   861 next
```
```   862   assume *: "\<forall>x\<in>C. \<forall>y\<in>C. \<forall>\<mu>. 0 \<le> \<mu> \<and> \<mu> \<le> 1 \<longrightarrow>
```
```   863     f (\<mu> *\<^sub>R x + (1 - \<mu>) *\<^sub>R y) \<le> \<mu> * f x + (1 - \<mu>) * f y"
```
```   864   {
```
```   865     fix x y
```
```   866     fix u v :: real
```
```   867     assume **: "x \<in> C" "y \<in> C" "u \<ge> 0" "v \<ge> 0" "u + v = 1"
```
```   868     then have[simp]: "1 - u = v" by auto
```
```   869     from *[rule_format, of x y u]
```
```   870     have "f (u *\<^sub>R x + v *\<^sub>R y) \<le> u * f x + v * f y"
```
```   871       using ** by auto
```
```   872   }
```
```   873   then show "convex_on C f"
```
```   874     unfolding convex_on_def by auto
```
```   875 qed
```
```   876
```
```   877 lemma convex_on_diff:
```
```   878   fixes f :: "real \<Rightarrow> real"
```
```   879   assumes f: "convex_on I f"
```
```   880     and I: "x \<in> I" "y \<in> I"
```
```   881     and t: "x < t" "t < y"
```
```   882   shows "(f x - f t) / (x - t) \<le> (f x - f y) / (x - y)"
```
```   883     and "(f x - f y) / (x - y) \<le> (f t - f y) / (t - y)"
```
```   884 proof -
```
```   885   define a where "a \<equiv> (t - y) / (x - y)"
```
```   886   with t have "0 \<le> a" "0 \<le> 1 - a"
```
```   887     by (auto simp: field_simps)
```
```   888   with f \<open>x \<in> I\<close> \<open>y \<in> I\<close> have cvx: "f (a * x + (1 - a) * y) \<le> a * f x + (1 - a) * f y"
```
```   889     by (auto simp: convex_on_def)
```
```   890   have "a * x + (1 - a) * y = a * (x - y) + y"
```
```   891     by (simp add: field_simps)
```
```   892   also have "\<dots> = t"
```
```   893     unfolding a_def using \<open>x < t\<close> \<open>t < y\<close> by simp
```
```   894   finally have "f t \<le> a * f x + (1 - a) * f y"
```
```   895     using cvx by simp
```
```   896   also have "\<dots> = a * (f x - f y) + f y"
```
```   897     by (simp add: field_simps)
```
```   898   finally have "f t - f y \<le> a * (f x - f y)"
```
```   899     by simp
```
```   900   with t show "(f x - f t) / (x - t) \<le> (f x - f y) / (x - y)"
```
```   901     by (simp add: le_divide_eq divide_le_eq field_simps a_def)
```
```   902   with t show "(f x - f y) / (x - y) \<le> (f t - f y) / (t - y)"
```
```   903     by (simp add: le_divide_eq divide_le_eq field_simps)
```
```   904 qed
```
```   905
```
```   906 lemma pos_convex_function:
```
```   907   fixes f :: "real \<Rightarrow> real"
```
```   908   assumes "convex C"
```
```   909     and leq: "\<And>x y. x \<in> C \<Longrightarrow> y \<in> C \<Longrightarrow> f' x * (y - x) \<le> f y - f x"
```
```   910   shows "convex_on C f"
```
```   911   unfolding convex_on_alt[OF assms(1)]
```
```   912   using assms
```
```   913 proof safe
```
```   914   fix x y \<mu> :: real
```
```   915   let ?x = "\<mu> *\<^sub>R x + (1 - \<mu>) *\<^sub>R y"
```
```   916   assume *: "convex C" "x \<in> C" "y \<in> C" "\<mu> \<ge> 0" "\<mu> \<le> 1"
```
```   917   then have "1 - \<mu> \<ge> 0" by auto
```
```   918   then have xpos: "?x \<in> C"
```
```   919     using * unfolding convex_alt by fastforce
```
```   920   have geq: "\<mu> * (f x - f ?x) + (1 - \<mu>) * (f y - f ?x) \<ge>
```
```   921       \<mu> * f' ?x * (x - ?x) + (1 - \<mu>) * f' ?x * (y - ?x)"
```
```   922     using add_mono [OF mult_left_mono [OF leq [OF xpos *(2)] \<open>\<mu> \<ge> 0\<close>]
```
```   923         mult_left_mono [OF leq [OF xpos *(3)] \<open>1 - \<mu> \<ge> 0\<close>]]
```
```   924     by auto
```
```   925   then have "\<mu> * f x + (1 - \<mu>) * f y - f ?x \<ge> 0"
```
```   926     by (auto simp: field_simps)
```
```   927   then show "f (\<mu> *\<^sub>R x + (1 - \<mu>) *\<^sub>R y) \<le> \<mu> * f x + (1 - \<mu>) * f y"
```
```   928     using convex_on_alt by auto
```
```   929 qed
```
```   930
```
```   931 lemma atMostAtLeast_subset_convex:
```
```   932   fixes C :: "real set"
```
```   933   assumes "convex C"
```
```   934     and "x \<in> C" "y \<in> C" "x < y"
```
```   935   shows "{x .. y} \<subseteq> C"
```
```   936 proof safe
```
```   937   fix z assume z: "z \<in> {x .. y}"
```
```   938   have less: "z \<in> C" if *: "x < z" "z < y"
```
```   939   proof -
```
```   940     let ?\<mu> = "(y - z) / (y - x)"
```
```   941     have "0 \<le> ?\<mu>" "?\<mu> \<le> 1"
```
```   942       using assms * by (auto simp: field_simps)
```
```   943     then have comb: "?\<mu> * x + (1 - ?\<mu>) * y \<in> C"
```
```   944       using assms iffD1[OF convex_alt, rule_format, of C y x ?\<mu>]
```
```   945       by (simp add: algebra_simps)
```
```   946     have "?\<mu> * x + (1 - ?\<mu>) * y = (y - z) * x / (y - x) + (1 - (y - z) / (y - x)) * y"
```
```   947       by (auto simp: field_simps)
```
```   948     also have "\<dots> = ((y - z) * x + (y - x - (y - z)) * y) / (y - x)"
```
```   949       using assms by (simp only: add_divide_distrib) (auto simp: field_simps)
```
```   950     also have "\<dots> = z"
```
```   951       using assms by (auto simp: field_simps)
```
```   952     finally show ?thesis
```
```   953       using comb by auto
```
```   954   qed
```
```   955   show "z \<in> C"
```
```   956     using z less assms by (auto simp: le_less)
```
```   957 qed
```
```   958
```
```   959 lemma f''_imp_f':
```
```   960   fixes f :: "real \<Rightarrow> real"
```
```   961   assumes "convex C"
```
```   962     and f': "\<And>x. x \<in> C \<Longrightarrow> DERIV f x :> (f' x)"
```
```   963     and f'': "\<And>x. x \<in> C \<Longrightarrow> DERIV f' x :> (f'' x)"
```
```   964     and pos: "\<And>x. x \<in> C \<Longrightarrow> f'' x \<ge> 0"
```
```   965     and x: "x \<in> C"
```
```   966     and y: "y \<in> C"
```
```   967   shows "f' x * (y - x) \<le> f y - f x"
```
```   968   using assms
```
```   969 proof -
```
```   970   have less_imp: "f y - f x \<ge> f' x * (y - x)" "f' y * (x - y) \<le> f x - f y"
```
```   971     if *: "x \<in> C" "y \<in> C" "y > x" for x y :: real
```
```   972   proof -
```
```   973     from * have ge: "y - x > 0" "y - x \<ge> 0"
```
```   974       by auto
```
```   975     from * have le: "x - y < 0" "x - y \<le> 0"
```
```   976       by auto
```
```   977     then obtain z1 where z1: "z1 > x" "z1 < y" "f y - f x = (y - x) * f' z1"
```
```   978       using subsetD[OF atMostAtLeast_subset_convex[OF \<open>convex C\<close> \<open>x \<in> C\<close> \<open>y \<in> C\<close> \<open>x < y\<close>],
```
```   979           THEN f', THEN MVT2[OF \<open>x < y\<close>, rule_format, unfolded atLeastAtMost_iff[symmetric]]]
```
```   980       by auto
```
```   981     then have "z1 \<in> C"
```
```   982       using atMostAtLeast_subset_convex \<open>convex C\<close> \<open>x \<in> C\<close> \<open>y \<in> C\<close> \<open>x < y\<close>
```
```   983       by fastforce
```
```   984     from z1 have z1': "f x - f y = (x - y) * f' z1"
```
```   985       by (simp add: field_simps)
```
```   986     obtain z2 where z2: "z2 > x" "z2 < z1" "f' z1 - f' x = (z1 - x) * f'' z2"
```
```   987       using subsetD[OF atMostAtLeast_subset_convex[OF \<open>convex C\<close> \<open>x \<in> C\<close> \<open>z1 \<in> C\<close> \<open>x < z1\<close>],
```
```   988           THEN f'', THEN MVT2[OF \<open>x < z1\<close>, rule_format, unfolded atLeastAtMost_iff[symmetric]]] z1
```
```   989       by auto
```
```   990     obtain z3 where z3: "z3 > z1" "z3 < y" "f' y - f' z1 = (y - z1) * f'' z3"
```
```   991       using subsetD[OF atMostAtLeast_subset_convex[OF \<open>convex C\<close> \<open>z1 \<in> C\<close> \<open>y \<in> C\<close> \<open>z1 < y\<close>],
```
```   992           THEN f'', THEN MVT2[OF \<open>z1 < y\<close>, rule_format, unfolded atLeastAtMost_iff[symmetric]]] z1
```
```   993       by auto
```
```   994     have "f' y - (f x - f y) / (x - y) = f' y - f' z1"
```
```   995       using * z1' by auto
```
```   996     also have "\<dots> = (y - z1) * f'' z3"
```
```   997       using z3 by auto
```
```   998     finally have cool': "f' y - (f x - f y) / (x - y) = (y - z1) * f'' z3"
```
```   999       by simp
```
```  1000     have A': "y - z1 \<ge> 0"
```
```  1001       using z1 by auto
```
```  1002     have "z3 \<in> C"
```
```  1003       using z3 * atMostAtLeast_subset_convex \<open>convex C\<close> \<open>x \<in> C\<close> \<open>z1 \<in> C\<close> \<open>x < z1\<close>
```
```  1004       by fastforce
```
```  1005     then have B': "f'' z3 \<ge> 0"
```
```  1006       using assms by auto
```
```  1007     from A' B' have "(y - z1) * f'' z3 \<ge> 0"
```
```  1008       by auto
```
```  1009     from cool' this have "f' y - (f x - f y) / (x - y) \<ge> 0"
```
```  1010       by auto
```
```  1011     from mult_right_mono_neg[OF this le(2)]
```
```  1012     have "f' y * (x - y) - (f x - f y) / (x - y) * (x - y) \<le> 0 * (x - y)"
```
```  1013       by (simp add: algebra_simps)
```
```  1014     then have "f' y * (x - y) - (f x - f y) \<le> 0"
```
```  1015       using le by auto
```
```  1016     then have res: "f' y * (x - y) \<le> f x - f y"
```
```  1017       by auto
```
```  1018     have "(f y - f x) / (y - x) - f' x = f' z1 - f' x"
```
```  1019       using * z1 by auto
```
```  1020     also have "\<dots> = (z1 - x) * f'' z2"
```
```  1021       using z2 by auto
```
```  1022     finally have cool: "(f y - f x) / (y - x) - f' x = (z1 - x) * f'' z2"
```
```  1023       by simp
```
```  1024     have A: "z1 - x \<ge> 0"
```
```  1025       using z1 by auto
```
```  1026     have "z2 \<in> C"
```
```  1027       using z2 z1 * atMostAtLeast_subset_convex \<open>convex C\<close> \<open>z1 \<in> C\<close> \<open>y \<in> C\<close> \<open>z1 < y\<close>
```
```  1028       by fastforce
```
```  1029     then have B: "f'' z2 \<ge> 0"
```
```  1030       using assms by auto
```
```  1031     from A B have "(z1 - x) * f'' z2 \<ge> 0"
```
```  1032       by auto
```
```  1033     with cool have "(f y - f x) / (y - x) - f' x \<ge> 0"
```
```  1034       by auto
```
```  1035     from mult_right_mono[OF this ge(2)]
```
```  1036     have "(f y - f x) / (y - x) * (y - x) - f' x * (y - x) \<ge> 0 * (y - x)"
```
```  1037       by (simp add: algebra_simps)
```
```  1038     then have "f y - f x - f' x * (y - x) \<ge> 0"
```
```  1039       using ge by auto
```
```  1040     then show "f y - f x \<ge> f' x * (y - x)" "f' y * (x - y) \<le> f x - f y"
```
```  1041       using res by auto
```
```  1042   qed
```
```  1043   show ?thesis
```
```  1044   proof (cases "x = y")
```
```  1045     case True
```
```  1046     with x y show ?thesis by auto
```
```  1047   next
```
```  1048     case False
```
```  1049     with less_imp x y show ?thesis
```
```  1050       by (auto simp: neq_iff)
```
```  1051   qed
```
```  1052 qed
```
```  1053
```
```  1054 lemma f''_ge0_imp_convex:
```
```  1055   fixes f :: "real \<Rightarrow> real"
```
```  1056   assumes conv: "convex C"
```
```  1057     and f': "\<And>x. x \<in> C \<Longrightarrow> DERIV f x :> (f' x)"
```
```  1058     and f'': "\<And>x. x \<in> C \<Longrightarrow> DERIV f' x :> (f'' x)"
```
```  1059     and pos: "\<And>x. x \<in> C \<Longrightarrow> f'' x \<ge> 0"
```
```  1060   shows "convex_on C f"
```
```  1061   using f''_imp_f'[OF conv f' f'' pos] assms pos_convex_function
```
```  1062   by fastforce
```
```  1063
```
```  1064 lemma minus_log_convex:
```
```  1065   fixes b :: real
```
```  1066   assumes "b > 1"
```
```  1067   shows "convex_on {0 <..} (\<lambda> x. - log b x)"
```
```  1068 proof -
```
```  1069   have "\<And>z. z > 0 \<Longrightarrow> DERIV (log b) z :> 1 / (ln b * z)"
```
```  1070     using DERIV_log by auto
```
```  1071   then have f': "\<And>z. z > 0 \<Longrightarrow> DERIV (\<lambda> z. - log b z) z :> - 1 / (ln b * z)"
```
```  1072     by (auto simp: DERIV_minus)
```
```  1073   have "\<And>z::real. z > 0 \<Longrightarrow> DERIV inverse z :> - (inverse z ^ Suc (Suc 0))"
```
```  1074     using less_imp_neq[THEN not_sym, THEN DERIV_inverse] by auto
```
```  1075   from this[THEN DERIV_cmult, of _ "- 1 / ln b"]
```
```  1076   have "\<And>z::real. z > 0 \<Longrightarrow>
```
```  1077     DERIV (\<lambda> z. (- 1 / ln b) * inverse z) z :> (- 1 / ln b) * (- (inverse z ^ Suc (Suc 0)))"
```
```  1078     by auto
```
```  1079   then have f''0: "\<And>z::real. z > 0 \<Longrightarrow>
```
```  1080     DERIV (\<lambda> z. - 1 / (ln b * z)) z :> 1 / (ln b * z * z)"
```
```  1081     unfolding inverse_eq_divide by (auto simp: mult.assoc)
```
```  1082   have f''_ge0: "\<And>z::real. z > 0 \<Longrightarrow> 1 / (ln b * z * z) \<ge> 0"
```
```  1083     using \<open>b > 1\<close> by (auto intro!: less_imp_le)
```
```  1084   from f''_ge0_imp_convex[OF pos_is_convex, unfolded greaterThan_iff, OF f' f''0 f''_ge0]
```
```  1085   show ?thesis
```
```  1086     by auto
```
```  1087 qed
```
```  1088
```
```  1089
```
```  1090 subsection%unimportant \<open>Convexity of real functions\<close>
```
```  1091
```
```  1092 lemma convex_on_realI:
```
```  1093   assumes "connected A"
```
```  1094     and "\<And>x. x \<in> A \<Longrightarrow> (f has_real_derivative f' x) (at x)"
```
```  1095     and "\<And>x y. x \<in> A \<Longrightarrow> y \<in> A \<Longrightarrow> x \<le> y \<Longrightarrow> f' x \<le> f' y"
```
```  1096   shows "convex_on A f"
```
```  1097 proof (rule convex_on_linorderI)
```
```  1098   fix t x y :: real
```
```  1099   assume t: "t > 0" "t < 1"
```
```  1100   assume xy: "x \<in> A" "y \<in> A" "x < y"
```
```  1101   define z where "z = (1 - t) * x + t * y"
```
```  1102   with \<open>connected A\<close> and xy have ivl: "{x..y} \<subseteq> A"
```
```  1103     using connected_contains_Icc by blast
```
```  1104
```
```  1105   from xy t have xz: "z > x"
```
```  1106     by (simp add: z_def algebra_simps)
```
```  1107   have "y - z = (1 - t) * (y - x)"
```
```  1108     by (simp add: z_def algebra_simps)
```
```  1109   also from xy t have "\<dots> > 0"
```
```  1110     by (intro mult_pos_pos) simp_all
```
```  1111   finally have yz: "z < y"
```
```  1112     by simp
```
```  1113
```
```  1114   from assms xz yz ivl t have "\<exists>\<xi>. \<xi> > x \<and> \<xi> < z \<and> f z - f x = (z - x) * f' \<xi>"
```
```  1115     by (intro MVT2) (auto intro!: assms(2))
```
```  1116   then obtain \<xi> where \<xi>: "\<xi> > x" "\<xi> < z" "f' \<xi> = (f z - f x) / (z - x)"
```
```  1117     by auto
```
```  1118   from assms xz yz ivl t have "\<exists>\<eta>. \<eta> > z \<and> \<eta> < y \<and> f y - f z = (y - z) * f' \<eta>"
```
```  1119     by (intro MVT2) (auto intro!: assms(2))
```
```  1120   then obtain \<eta> where \<eta>: "\<eta> > z" "\<eta> < y" "f' \<eta> = (f y - f z) / (y - z)"
```
```  1121     by auto
```
```  1122
```
```  1123   from \<eta>(3) have "(f y - f z) / (y - z) = f' \<eta>" ..
```
```  1124   also from \<xi> \<eta> ivl have "\<xi> \<in> A" "\<eta> \<in> A"
```
```  1125     by auto
```
```  1126   with \<xi> \<eta> have "f' \<eta> \<ge> f' \<xi>"
```
```  1127     by (intro assms(3)) auto
```
```  1128   also from \<xi>(3) have "f' \<xi> = (f z - f x) / (z - x)" .
```
```  1129   finally have "(f y - f z) * (z - x) \<ge> (f z - f x) * (y - z)"
```
```  1130     using xz yz by (simp add: field_simps)
```
```  1131   also have "z - x = t * (y - x)"
```
```  1132     by (simp add: z_def algebra_simps)
```
```  1133   also have "y - z = (1 - t) * (y - x)"
```
```  1134     by (simp add: z_def algebra_simps)
```
```  1135   finally have "(f y - f z) * t \<ge> (f z - f x) * (1 - t)"
```
```  1136     using xy by simp
```
```  1137   then show "(1 - t) * f x + t * f y \<ge> f ((1 - t) *\<^sub>R x + t *\<^sub>R y)"
```
```  1138     by (simp add: z_def algebra_simps)
```
```  1139 qed
```
```  1140
```
```  1141 lemma convex_on_inverse:
```
```  1142   assumes "A \<subseteq> {0<..}"
```
```  1143   shows "convex_on A (inverse :: real \<Rightarrow> real)"
```
```  1144 proof (rule convex_on_subset[OF _ assms], intro convex_on_realI[of _ _ "\<lambda>x. -inverse (x^2)"])
```
```  1145   fix u v :: real
```
```  1146   assume "u \<in> {0<..}" "v \<in> {0<..}" "u \<le> v"
```
```  1147   with assms show "-inverse (u^2) \<le> -inverse (v^2)"
```
```  1148     by (intro le_imp_neg_le le_imp_inverse_le power_mono) (simp_all)
```
```  1149 qed (insert assms, auto intro!: derivative_eq_intros simp: divide_simps power2_eq_square)
```
```  1150
```
```  1151 lemma convex_onD_Icc':
```
```  1152   assumes "convex_on {x..y} f" "c \<in> {x..y}"
```
```  1153   defines "d \<equiv> y - x"
```
```  1154   shows "f c \<le> (f y - f x) / d * (c - x) + f x"
```
```  1155 proof (cases x y rule: linorder_cases)
```
```  1156   case less
```
```  1157   then have d: "d > 0"
```
```  1158     by (simp add: d_def)
```
```  1159   from assms(2) less have A: "0 \<le> (c - x) / d" "(c - x) / d \<le> 1"
```
```  1160     by (simp_all add: d_def divide_simps)
```
```  1161   have "f c = f (x + (c - x) * 1)"
```
```  1162     by simp
```
```  1163   also from less have "1 = ((y - x) / d)"
```
```  1164     by (simp add: d_def)
```
```  1165   also from d have "x + (c - x) * \<dots> = (1 - (c - x) / d) *\<^sub>R x + ((c - x) / d) *\<^sub>R y"
```
```  1166     by (simp add: field_simps)
```
```  1167   also have "f \<dots> \<le> (1 - (c - x) / d) * f x + (c - x) / d * f y"
```
```  1168     using assms less by (intro convex_onD_Icc) simp_all
```
```  1169   also from d have "\<dots> = (f y - f x) / d * (c - x) + f x"
```
```  1170     by (simp add: field_simps)
```
```  1171   finally show ?thesis .
```
```  1172 qed (insert assms(2), simp_all)
```
```  1173
```
```  1174 lemma convex_onD_Icc'':
```
```  1175   assumes "convex_on {x..y} f" "c \<in> {x..y}"
```
```  1176   defines "d \<equiv> y - x"
```
```  1177   shows "f c \<le> (f x - f y) / d * (y - c) + f y"
```
```  1178 proof (cases x y rule: linorder_cases)
```
```  1179   case less
```
```  1180   then have d: "d > 0"
```
```  1181     by (simp add: d_def)
```
```  1182   from assms(2) less have A: "0 \<le> (y - c) / d" "(y - c) / d \<le> 1"
```
```  1183     by (simp_all add: d_def divide_simps)
```
```  1184   have "f c = f (y - (y - c) * 1)"
```
```  1185     by simp
```
```  1186   also from less have "1 = ((y - x) / d)"
```
```  1187     by (simp add: d_def)
```
```  1188   also from d have "y - (y - c) * \<dots> = (1 - (1 - (y - c) / d)) *\<^sub>R x + (1 - (y - c) / d) *\<^sub>R y"
```
```  1189     by (simp add: field_simps)
```
```  1190   also have "f \<dots> \<le> (1 - (1 - (y - c) / d)) * f x + (1 - (y - c) / d) * f y"
```
```  1191     using assms less by (intro convex_onD_Icc) (simp_all add: field_simps)
```
```  1192   also from d have "\<dots> = (f x - f y) / d * (y - c) + f y"
```
```  1193     by (simp add: field_simps)
```
```  1194   finally show ?thesis .
```
```  1195 qed (insert assms(2), simp_all)
```
```  1196
```
```  1197 lemma convex_supp_sum:
```
```  1198   assumes "convex S" and 1: "supp_sum u I = 1"
```
```  1199       and "\<And>i. i \<in> I \<Longrightarrow> 0 \<le> u i \<and> (u i = 0 \<or> f i \<in> S)"
```
```  1200     shows "supp_sum (\<lambda>i. u i *\<^sub>R f i) I \<in> S"
```
```  1201 proof -
```
```  1202   have fin: "finite {i \<in> I. u i \<noteq> 0}"
```
```  1203     using 1 sum.infinite by (force simp: supp_sum_def support_on_def)
```
```  1204   then have eq: "supp_sum (\<lambda>i. u i *\<^sub>R f i) I = sum (\<lambda>i. u i *\<^sub>R f i) {i \<in> I. u i \<noteq> 0}"
```
```  1205     by (force intro: sum.mono_neutral_left simp: supp_sum_def support_on_def)
```
```  1206   show ?thesis
```
```  1207     apply (simp add: eq)
```
```  1208     apply (rule convex_sum [OF fin \<open>convex S\<close>])
```
```  1209     using 1 assms apply (auto simp: supp_sum_def support_on_def)
```
```  1210     done
```
```  1211 qed
```
```  1212
```
```  1213 lemma convex_translation_eq [simp]: "convex ((\<lambda>x. a + x) ` s) \<longleftrightarrow> convex s"
```
```  1214   by (metis convex_translation translation_galois)
```
```  1215
```
```  1216 lemma convex_linear_image_eq [simp]:
```
```  1217     fixes f :: "'a::real_vector \<Rightarrow> 'b::real_vector"
```
```  1218     shows "\<lbrakk>linear f; inj f\<rbrakk> \<Longrightarrow> convex (f ` s) \<longleftrightarrow> convex s"
```
```  1219     by (metis (no_types) convex_linear_image convex_linear_vimage inj_vimage_image_eq)
```
```  1220
```
```  1221 lemma basis_to_basis_subspace_isomorphism:
```
```  1222   assumes s: "subspace (S:: ('n::euclidean_space) set)"
```
```  1223     and t: "subspace (T :: ('m::euclidean_space) set)"
```
```  1224     and d: "dim S = dim T"
```
```  1225     and B: "B \<subseteq> S" "independent B" "S \<subseteq> span B" "card B = dim S"
```
```  1226     and C: "C \<subseteq> T" "independent C" "T \<subseteq> span C" "card C = dim T"
```
```  1227   shows "\<exists>f. linear f \<and> f ` B = C \<and> f ` S = T \<and> inj_on f S"
```
```  1228 proof -
```
```  1229   from B independent_bound have fB: "finite B"
```
```  1230     by blast
```
```  1231   from C independent_bound have fC: "finite C"
```
```  1232     by blast
```
```  1233   from B(4) C(4) card_le_inj[of B C] d obtain f where
```
```  1234     f: "f ` B \<subseteq> C" "inj_on f B" using \<open>finite B\<close> \<open>finite C\<close> by auto
```
```  1235   from linear_independent_extend[OF B(2)] obtain g where
```
```  1236     g: "linear g" "\<forall>x \<in> B. g x = f x" by blast
```
```  1237   from inj_on_iff_eq_card[OF fB, of f] f(2)
```
```  1238   have "card (f ` B) = card B" by simp
```
```  1239   with B(4) C(4) have ceq: "card (f ` B) = card C" using d
```
```  1240     by simp
```
```  1241   have "g ` B = f ` B" using g(2)
```
```  1242     by (auto simp add: image_iff)
```
```  1243   also have "\<dots> = C" using card_subset_eq[OF fC f(1) ceq] .
```
```  1244   finally have gBC: "g ` B = C" .
```
```  1245   have gi: "inj_on g B" using f(2) g(2)
```
```  1246     by (auto simp add: inj_on_def)
```
```  1247   note g0 = linear_indep_image_lemma[OF g(1) fB, unfolded gBC, OF C(2) gi]
```
```  1248   {
```
```  1249     fix x y
```
```  1250     assume x: "x \<in> S" and y: "y \<in> S" and gxy: "g x = g y"
```
```  1251     from B(3) x y have x': "x \<in> span B" and y': "y \<in> span B"
```
```  1252       by blast+
```
```  1253     from gxy have th0: "g (x - y) = 0"
```
```  1254       by (simp add: linear_diff[OF g(1)])
```
```  1255     have th1: "x - y \<in> span B" using x' y'
```
```  1256       by (metis span_diff)
```
```  1257     have "x = y" using g0[OF th1 th0] by simp
```
```  1258   }
```
```  1259   then have giS: "inj_on g S" unfolding inj_on_def by blast
```
```  1260   from span_subspace[OF B(1,3) s]
```
```  1261   have "g ` S = span (g ` B)"
```
```  1262     by (simp add: span_linear_image[OF g(1)])
```
```  1263   also have "\<dots> = span C"
```
```  1264     unfolding gBC ..
```
```  1265   also have "\<dots> = T"
```
```  1266     using span_subspace[OF C(1,3) t] .
```
```  1267   finally have gS: "g ` S = T" .
```
```  1268   from g(1) gS giS gBC show ?thesis
```
```  1269     by blast
```
```  1270 qed
```
```  1271
```
```  1272 lemma closure_bounded_linear_image_subset:
```
```  1273   assumes f: "bounded_linear f"
```
```  1274   shows "f ` closure S \<subseteq> closure (f ` S)"
```
```  1275   using linear_continuous_on [OF f] closed_closure closure_subset
```
```  1276   by (rule image_closure_subset)
```
```  1277
```
```  1278 lemma closure_linear_image_subset:
```
```  1279   fixes f :: "'m::euclidean_space \<Rightarrow> 'n::real_normed_vector"
```
```  1280   assumes "linear f"
```
```  1281   shows "f ` (closure S) \<subseteq> closure (f ` S)"
```
```  1282   using assms unfolding linear_conv_bounded_linear
```
```  1283   by (rule closure_bounded_linear_image_subset)
```
```  1284
```
```  1285 lemma closed_injective_linear_image:
```
```  1286     fixes f :: "'a::euclidean_space \<Rightarrow> 'b::euclidean_space"
```
```  1287     assumes S: "closed S" and f: "linear f" "inj f"
```
```  1288     shows "closed (f ` S)"
```
```  1289 proof -
```
```  1290   obtain g where g: "linear g" "g \<circ> f = id"
```
```  1291     using linear_injective_left_inverse [OF f] by blast
```
```  1292   then have confg: "continuous_on (range f) g"
```
```  1293     using linear_continuous_on linear_conv_bounded_linear by blast
```
```  1294   have [simp]: "g ` f ` S = S"
```
```  1295     using g by (simp add: image_comp)
```
```  1296   have cgf: "closed (g ` f ` S)"
```
```  1297     by (simp add: \<open>g \<circ> f = id\<close> S image_comp)
```
```  1298   have [simp]: "(range f \<inter> g -` S) = f ` S"
```
```  1299     using g unfolding o_def id_def image_def by auto metis+
```
```  1300   show ?thesis
```
```  1301   proof (rule closedin_closed_trans [of "range f"])
```
```  1302     show "closedin (subtopology euclidean (range f)) (f ` S)"
```
```  1303       using continuous_closedin_preimage [OF confg cgf] by simp
```
```  1304     show "closed (range f)"
```
```  1305       apply (rule closed_injective_image_subspace)
```
```  1306       using f apply (auto simp: linear_linear linear_injective_0)
```
```  1307       done
```
```  1308   qed
```
```  1309 qed
```
```  1310
```
```  1311 lemma closed_injective_linear_image_eq:
```
```  1312     fixes f :: "'a::euclidean_space \<Rightarrow> 'b::euclidean_space"
```
```  1313     assumes f: "linear f" "inj f"
```
```  1314       shows "(closed(image f s) \<longleftrightarrow> closed s)"
```
```  1315   by (metis closed_injective_linear_image closure_eq closure_linear_image_subset closure_subset_eq f(1) f(2) inj_image_subset_iff)
```
```  1316
```
```  1317 lemma closure_injective_linear_image:
```
```  1318     fixes f :: "'a::euclidean_space \<Rightarrow> 'b::euclidean_space"
```
```  1319     shows "\<lbrakk>linear f; inj f\<rbrakk> \<Longrightarrow> f ` (closure S) = closure (f ` S)"
```
```  1320   apply (rule subset_antisym)
```
```  1321   apply (simp add: closure_linear_image_subset)
```
```  1322   by (simp add: closure_minimal closed_injective_linear_image closure_subset image_mono)
```
```  1323
```
```  1324 lemma closure_bounded_linear_image:
```
```  1325     fixes f :: "'a::euclidean_space \<Rightarrow> 'b::euclidean_space"
```
```  1326     shows "\<lbrakk>linear f; bounded S\<rbrakk> \<Longrightarrow> f ` (closure S) = closure (f ` S)"
```
```  1327   apply (rule subset_antisym, simp add: closure_linear_image_subset)
```
```  1328   apply (rule closure_minimal, simp add: closure_subset image_mono)
```
```  1329   by (meson bounded_closure closed_closure compact_continuous_image compact_eq_bounded_closed linear_continuous_on linear_conv_bounded_linear)
```
```  1330
```
```  1331 lemma closure_scaleR:
```
```  1332   fixes S :: "'a::real_normed_vector set"
```
```  1333   shows "(( *\<^sub>R) c) ` (closure S) = closure ((( *\<^sub>R) c) ` S)"
```
```  1334 proof
```
```  1335   show "(( *\<^sub>R) c) ` (closure S) \<subseteq> closure ((( *\<^sub>R) c) ` S)"
```
```  1336     using bounded_linear_scaleR_right
```
```  1337     by (rule closure_bounded_linear_image_subset)
```
```  1338   show "closure ((( *\<^sub>R) c) ` S) \<subseteq> (( *\<^sub>R) c) ` (closure S)"
```
```  1339     by (intro closure_minimal image_mono closure_subset closed_scaling closed_closure)
```
```  1340 qed
```
```  1341
```
```  1342 lemma fst_linear: "linear fst"
```
```  1343   unfolding linear_iff by (simp add: algebra_simps)
```
```  1344
```
```  1345 lemma snd_linear: "linear snd"
```
```  1346   unfolding linear_iff by (simp add: algebra_simps)
```
```  1347
```
```  1348 lemma fst_snd_linear: "linear (\<lambda>(x,y). x + y)"
```
```  1349   unfolding linear_iff by (simp add: algebra_simps)
```
```  1350
```
```  1351 lemma vector_choose_size:
```
```  1352   assumes "0 \<le> c"
```
```  1353   obtains x :: "'a::{real_normed_vector, perfect_space}" where "norm x = c"
```
```  1354 proof -
```
```  1355   obtain a::'a where "a \<noteq> 0"
```
```  1356     using UNIV_not_singleton UNIV_eq_I set_zero singletonI by fastforce
```
```  1357   then show ?thesis
```
```  1358     by (rule_tac x="scaleR (c / norm a) a" in that) (simp add: assms)
```
```  1359 qed
```
```  1360
```
```  1361 lemma vector_choose_dist:
```
```  1362   assumes "0 \<le> c"
```
```  1363   obtains y :: "'a::{real_normed_vector, perfect_space}" where "dist x y = c"
```
```  1364 by (metis add_diff_cancel_left' assms dist_commute dist_norm vector_choose_size)
```
```  1365
```
```  1366 lemma sphere_eq_empty [simp]:
```
```  1367   fixes a :: "'a::{real_normed_vector, perfect_space}"
```
```  1368   shows "sphere a r = {} \<longleftrightarrow> r < 0"
```
```  1369 by (auto simp: sphere_def dist_norm) (metis dist_norm le_less_linear vector_choose_dist)
```
```  1370
```
```  1371 lemma sum_delta_notmem:
```
```  1372   assumes "x \<notin> s"
```
```  1373   shows "sum (\<lambda>y. if (y = x) then P x else Q y) s = sum Q s"
```
```  1374     and "sum (\<lambda>y. if (x = y) then P x else Q y) s = sum Q s"
```
```  1375     and "sum (\<lambda>y. if (y = x) then P y else Q y) s = sum Q s"
```
```  1376     and "sum (\<lambda>y. if (x = y) then P y else Q y) s = sum Q s"
```
```  1377   apply (rule_tac [!] sum.cong)
```
```  1378   using assms
```
```  1379   apply auto
```
```  1380   done
```
```  1381
```
```  1382 lemma sum_delta'':
```
```  1383   fixes s::"'a::real_vector set"
```
```  1384   assumes "finite s"
```
```  1385   shows "(\<Sum>x\<in>s. (if y = x then f x else 0) *\<^sub>R x) = (if y\<in>s then (f y) *\<^sub>R y else 0)"
```
```  1386 proof -
```
```  1387   have *: "\<And>x y. (if y = x then f x else (0::real)) *\<^sub>R x = (if x=y then (f x) *\<^sub>R x else 0)"
```
```  1388     by auto
```
```  1389   show ?thesis
```
```  1390     unfolding * using sum.delta[OF assms, of y "\<lambda>x. f x *\<^sub>R x"] by auto
```
```  1391 qed
```
```  1392
```
```  1393 lemma if_smult: "(if P then x else (y::real)) *\<^sub>R v = (if P then x *\<^sub>R v else y *\<^sub>R v)"
```
```  1394   by (fact if_distrib)
```
```  1395
```
```  1396 lemma dist_triangle_eq:
```
```  1397   fixes x y z :: "'a::real_inner"
```
```  1398   shows "dist x z = dist x y + dist y z \<longleftrightarrow>
```
```  1399     norm (x - y) *\<^sub>R (y - z) = norm (y - z) *\<^sub>R (x - y)"
```
```  1400 proof -
```
```  1401   have *: "x - y + (y - z) = x - z" by auto
```
```  1402   show ?thesis unfolding dist_norm norm_triangle_eq[of "x - y" "y - z", unfolded *]
```
```  1403     by (auto simp add:norm_minus_commute)
```
```  1404 qed
```
```  1405
```
```  1406
```
```  1407 subsection \<open>Affine set and affine hull\<close>
```
```  1408
```
```  1409 definition%important affine :: "'a::real_vector set \<Rightarrow> bool"
```
```  1410   where "affine s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u v. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> s)"
```
```  1411
```
```  1412 lemma affine_alt: "affine s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. \<forall>u::real. (1 - u) *\<^sub>R x + u *\<^sub>R y \<in> s)"
```
```  1413   unfolding affine_def by (metis eq_diff_eq')
```
```  1414
```
```  1415 lemma affine_empty [iff]: "affine {}"
```
```  1416   unfolding affine_def by auto
```
```  1417
```
```  1418 lemma affine_sing [iff]: "affine {x}"
```
```  1419   unfolding affine_alt by (auto simp add: scaleR_left_distrib [symmetric])
```
```  1420
```
```  1421 lemma affine_UNIV [iff]: "affine UNIV"
```
```  1422   unfolding affine_def by auto
```
```  1423
```
```  1424 lemma affine_Inter [intro]: "(\<And>s. s\<in>f \<Longrightarrow> affine s) \<Longrightarrow> affine (\<Inter>f)"
```
```  1425   unfolding affine_def by auto
```
```  1426
```
```  1427 lemma affine_Int[intro]: "affine s \<Longrightarrow> affine t \<Longrightarrow> affine (s \<inter> t)"
```
```  1428   unfolding affine_def by auto
```
```  1429
```
```  1430 lemma affine_scaling: "affine s \<Longrightarrow> affine (image (\<lambda>x. c *\<^sub>R x) s)"
```
```  1431   apply (clarsimp simp add: affine_def)
```
```  1432   apply (rule_tac x="u *\<^sub>R x + v *\<^sub>R y" in image_eqI)
```
```  1433   apply (auto simp: algebra_simps)
```
```  1434   done
```
```  1435
```
```  1436 lemma affine_affine_hull [simp]: "affine(affine hull s)"
```
```  1437   unfolding hull_def
```
```  1438   using affine_Inter[of "{t. affine t \<and> s \<subseteq> t}"] by auto
```
```  1439
```
```  1440 lemma affine_hull_eq[simp]: "(affine hull s = s) \<longleftrightarrow> affine s"
```
```  1441   by (metis affine_affine_hull hull_same)
```
```  1442
```
```  1443 lemma affine_hyperplane: "affine {x. a \<bullet> x = b}"
```
```  1444   by (simp add: affine_def algebra_simps) (metis distrib_right mult.left_neutral)
```
```  1445
```
```  1446
```
```  1447 subsubsection%unimportant \<open>Some explicit formulations (from Lars Schewe)\<close>
```
```  1448
```
```  1449 lemma affine:
```
```  1450   fixes V::"'a::real_vector set"
```
```  1451   shows "affine V \<longleftrightarrow>
```
```  1452     (\<forall>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> V \<and> sum u s = 1 \<longrightarrow> (sum (\<lambda>x. (u x) *\<^sub>R x)) s \<in> V)"
```
```  1453   unfolding affine_def
```
```  1454   apply rule
```
```  1455   apply(rule, rule, rule)
```
```  1456   apply(erule conjE)+
```
```  1457   defer
```
```  1458   apply (rule, rule, rule, rule, rule)
```
```  1459 proof -
```
```  1460   fix x y u v
```
```  1461   assume as: "x \<in> V" "y \<in> V" "u + v = (1::real)"
```
```  1462     "\<forall>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> V \<and> sum u s = 1 \<longrightarrow> (\<Sum>x\<in>s. u x *\<^sub>R x) \<in> V"
```
```  1463   then show "u *\<^sub>R x + v *\<^sub>R y \<in> V"
```
```  1464     apply (cases "x = y")
```
```  1465     using as(4)[THEN spec[where x="{x,y}"], THEN spec[where x="\<lambda>w. if w = x then u else v"]]
```
```  1466       and as(1-3)
```
```  1467     apply (auto simp add: scaleR_left_distrib[symmetric])
```
```  1468     done
```
```  1469 next
```
```  1470   fix s u
```
```  1471   assume as: "\<forall>x\<in>V. \<forall>y\<in>V. \<forall>u v. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> V"
```
```  1472     "finite s" "s \<noteq> {}" "s \<subseteq> V" "sum u s = (1::real)"
```
```  1473   define n where "n = card s"
```
```  1474   have "card s = 0 \<or> card s = 1 \<or> card s = 2 \<or> card s > 2" by auto
```
```  1475   then show "(\<Sum>x\<in>s. u x *\<^sub>R x) \<in> V"
```
```  1476   proof (auto simp only: disjE)
```
```  1477     assume "card s = 2"
```
```  1478     then have "card s = Suc (Suc 0)"
```
```  1479       by auto
```
```  1480     then obtain a b where "s = {a, b}"
```
```  1481       unfolding card_Suc_eq by auto
```
```  1482     then show ?thesis
```
```  1483       using as(1)[THEN bspec[where x=a], THEN bspec[where x=b]] using as(4,5)
```
```  1484       by (auto simp add: sum_clauses(2))
```
```  1485   next
```
```  1486     assume "card s > 2"
```
```  1487     then show ?thesis using as and n_def
```
```  1488     proof (induct n arbitrary: u s)
```
```  1489       case 0
```
```  1490       then show ?case by auto
```
```  1491     next
```
```  1492       case (Suc n)
```
```  1493       fix s :: "'a set" and u :: "'a \<Rightarrow> real"
```
```  1494       assume IA:
```
```  1495         "\<And>u s.  \<lbrakk>2 < card s; \<forall>x\<in>V. \<forall>y\<in>V. \<forall>u v. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> V; finite s;
```
```  1496           s \<noteq> {}; s \<subseteq> V; sum u s = 1; n = card s \<rbrakk> \<Longrightarrow> (\<Sum>x\<in>s. u x *\<^sub>R x) \<in> V"
```
```  1497         and as:
```
```  1498           "Suc n = card s" "2 < card s" "\<forall>x\<in>V. \<forall>y\<in>V. \<forall>u v. u + v = 1 \<longrightarrow> u *\<^sub>R x + v *\<^sub>R y \<in> V"
```
```  1499            "finite s" "s \<noteq> {}" "s \<subseteq> V" "sum u s = 1"
```
```  1500       have "\<exists>x\<in>s. u x \<noteq> 1"
```
```  1501       proof (rule ccontr)
```
```  1502         assume "\<not> ?thesis"
```
```  1503         then have "sum u s = real_of_nat (card s)"
```
```  1504           unfolding card_eq_sum by auto
```
```  1505         then show False
```
```  1506           using as(7) and \<open>card s > 2\<close>
```
```  1507           by (metis One_nat_def less_Suc0 Zero_not_Suc of_nat_1 of_nat_eq_iff numeral_2_eq_2)
```
```  1508       qed
```
```  1509       then obtain x where x:"x \<in> s" "u x \<noteq> 1" by auto
```
```  1510
```
```  1511       have c: "card (s - {x}) = card s - 1"
```
```  1512         apply (rule card_Diff_singleton)
```
```  1513         using \<open>x\<in>s\<close> as(4)
```
```  1514         apply auto
```
```  1515         done
```
```  1516       have *: "s = insert x (s - {x})" "finite (s - {x})"
```
```  1517         using \<open>x\<in>s\<close> and as(4) by auto
```
```  1518       have **: "sum u (s - {x}) = 1 - u x"
```
```  1519         using sum_clauses(2)[OF *(2), of u x, unfolded *(1)[symmetric] as(7)] by auto
```
```  1520       have ***: "inverse (1 - u x) * sum u (s - {x}) = 1"
```
```  1521         unfolding ** using \<open>u x \<noteq> 1\<close> by auto
```
```  1522       have "(\<Sum>xa\<in>s - {x}. (inverse (1 - u x) * u xa) *\<^sub>R xa) \<in> V"
```
```  1523       proof (cases "card (s - {x}) > 2")
```
```  1524         case True
```
```  1525         then have "s - {x} \<noteq> {}" "card (s - {x}) = n"
```
```  1526           unfolding c and as(1)[symmetric]
```
```  1527         proof (rule_tac ccontr)
```
```  1528           assume "\<not> s - {x} \<noteq> {}"
```
```  1529           then have "card (s - {x}) = 0" unfolding card_0_eq[OF *(2)] by simp
```
```  1530           then show False using True by auto
```
```  1531         qed auto
```
```  1532         then show ?thesis
```
```  1533           apply (rule_tac IA[of "s - {x}" "\<lambda>y. (inverse (1 - u x) * u y)"])
```
```  1534           unfolding sum_distrib_left[symmetric]
```
```  1535           using as and *** and True
```
```  1536           apply auto
```
```  1537           done
```
```  1538       next
```
```  1539         case False
```
```  1540         then have "card (s - {x}) = Suc (Suc 0)"
```
```  1541           using as(2) and c by auto
```
```  1542         then obtain a b where "(s - {x}) = {a, b}" "a\<noteq>b"
```
```  1543           unfolding card_Suc_eq by auto
```
```  1544         then show ?thesis
```
```  1545           using as(3)[THEN bspec[where x=a], THEN bspec[where x=b]]
```
```  1546           using *** *(2) and \<open>s \<subseteq> V\<close>
```
```  1547           unfolding sum_distrib_left
```
```  1548           by (auto simp add: sum_clauses(2))
```
```  1549       qed
```
```  1550       then have "u x + (1 - u x) = 1 \<Longrightarrow>
```
```  1551           u x *\<^sub>R x + (1 - u x) *\<^sub>R ((\<Sum>xa\<in>s - {x}. u xa *\<^sub>R xa) /\<^sub>R (1 - u x)) \<in> V"
```
```  1552         apply -
```
```  1553         apply (rule as(3)[rule_format])
```
```  1554         unfolding  Real_Vector_Spaces.scaleR_right.sum
```
```  1555         using x(1) as(6)
```
```  1556         apply auto
```
```  1557         done
```
```  1558       then show "(\<Sum>x\<in>s. u x *\<^sub>R x) \<in> V"
```
```  1559         unfolding scaleR_scaleR[symmetric] and scaleR_right.sum [symmetric]
```
```  1560         apply (subst *)
```
```  1561         unfolding sum_clauses(2)[OF *(2)]
```
```  1562         using \<open>u x \<noteq> 1\<close>
```
```  1563         apply auto
```
```  1564         done
```
```  1565     qed
```
```  1566   next
```
```  1567     assume "card s = 1"
```
```  1568     then obtain a where "s={a}"
```
```  1569       by (auto simp add: card_Suc_eq)
```
```  1570     then show ?thesis
```
```  1571       using as(4,5) by simp
```
```  1572   qed (insert \<open>s\<noteq>{}\<close> \<open>finite s\<close>, auto)
```
```  1573 qed
```
```  1574
```
```  1575 lemma affine_hull_explicit:
```
```  1576   "affine hull p =
```
```  1577     {y. \<exists>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p \<and> sum u s = 1 \<and> sum (\<lambda>v. (u v) *\<^sub>R v) s = y}"
```
```  1578   apply (rule hull_unique)
```
```  1579   apply (subst subset_eq)
```
```  1580   prefer 3
```
```  1581   apply rule
```
```  1582   unfolding mem_Collect_eq
```
```  1583   apply (erule exE)+
```
```  1584   apply (erule conjE)+
```
```  1585   prefer 2
```
```  1586   apply rule
```
```  1587 proof -
```
```  1588   fix x
```
```  1589   assume "x\<in>p"
```
```  1590   then show "\<exists>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p \<and> sum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = x"
```
```  1591     apply (rule_tac x="{x}" in exI)
```
```  1592     apply (rule_tac x="\<lambda>x. 1" in exI)
```
```  1593     apply auto
```
```  1594     done
```
```  1595 next
```
```  1596   fix t x s u
```
```  1597   assume as: "p \<subseteq> t" "affine t" "finite s" "s \<noteq> {}"
```
```  1598     "s \<subseteq> p" "sum u s = 1" "(\<Sum>v\<in>s. u v *\<^sub>R v) = x"
```
```  1599   then show "x \<in> t"
```
```  1600     using as(2)[unfolded affine, THEN spec[where x=s], THEN spec[where x=u]]
```
```  1601     by auto
```
```  1602 next
```
```  1603   show "affine {y. \<exists>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p \<and> sum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = y}"
```
```  1604     unfolding affine_def
```
```  1605     apply (rule, rule, rule, rule, rule)
```
```  1606     unfolding mem_Collect_eq
```
```  1607   proof -
```
```  1608     fix u v :: real
```
```  1609     assume uv: "u + v = 1"
```
```  1610     fix x
```
```  1611     assume "\<exists>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p \<and> sum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = x"
```
```  1612     then obtain sx ux where
```
```  1613       x: "finite sx" "sx \<noteq> {}" "sx \<subseteq> p" "sum ux sx = 1" "(\<Sum>v\<in>sx. ux v *\<^sub>R v) = x"
```
```  1614       by auto
```
```  1615     fix y
```
```  1616     assume "\<exists>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p \<and> sum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = y"
```
```  1617     then obtain sy uy where
```
```  1618       y: "finite sy" "sy \<noteq> {}" "sy \<subseteq> p" "sum uy sy = 1" "(\<Sum>v\<in>sy. uy v *\<^sub>R v) = y" by auto
```
```  1619     have xy: "finite (sx \<union> sy)"
```
```  1620       using x(1) y(1) by auto
```
```  1621     have **: "(sx \<union> sy) \<inter> sx = sx" "(sx \<union> sy) \<inter> sy = sy"
```
```  1622       by auto
```
```  1623     show "\<exists>s ua. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p \<and>
```
```  1624         sum ua s = 1 \<and> (\<Sum>v\<in>s. ua v *\<^sub>R v) = u *\<^sub>R x + v *\<^sub>R y"
```
```  1625       apply (rule_tac x="sx \<union> sy" in exI)
```
```  1626       apply (rule_tac x="\<lambda>a. (if a\<in>sx then u * ux a else 0) + (if a\<in>sy then v * uy a else 0)" in exI)
```
```  1627       unfolding scaleR_left_distrib sum.distrib if_smult scaleR_zero_left
```
```  1628         ** sum.inter_restrict[OF xy, symmetric]
```
```  1629       unfolding scaleR_scaleR[symmetric] Real_Vector_Spaces.scaleR_right.sum [symmetric]
```
```  1630         and sum_distrib_left[symmetric]
```
```  1631       unfolding x y
```
```  1632       using x(1-3) y(1-3) uv
```
```  1633       apply simp
```
```  1634       done
```
```  1635   qed
```
```  1636 qed
```
```  1637
```
```  1638 lemma affine_hull_finite:
```
```  1639   assumes "finite s"
```
```  1640   shows "affine hull s = {y. \<exists>u. sum u s = 1 \<and> sum (\<lambda>v. u v *\<^sub>R v) s = y}"
```
```  1641   unfolding affine_hull_explicit and set_eq_iff and mem_Collect_eq
```
```  1642   apply (rule, rule)
```
```  1643   apply (erule exE)+
```
```  1644   apply (erule conjE)+
```
```  1645   defer
```
```  1646   apply (erule exE)
```
```  1647   apply (erule conjE)
```
```  1648 proof -
```
```  1649   fix x u
```
```  1650   assume "sum u s = 1" "(\<Sum>v\<in>s. u v *\<^sub>R v) = x"
```
```  1651   then show "\<exists>sa u. finite sa \<and>
```
```  1652       \<not> (\<forall>x. (x \<in> sa) = (x \<in> {})) \<and> sa \<subseteq> s \<and> sum u sa = 1 \<and> (\<Sum>v\<in>sa. u v *\<^sub>R v) = x"
```
```  1653     apply (rule_tac x=s in exI, rule_tac x=u in exI)
```
```  1654     using assms
```
```  1655     apply auto
```
```  1656     done
```
```  1657 next
```
```  1658   fix x t u
```
```  1659   assume "t \<subseteq> s"
```
```  1660   then have *: "s \<inter> t = t"
```
```  1661     by auto
```
```  1662   assume "finite t" "\<not> (\<forall>x. (x \<in> t) = (x \<in> {}))" "sum u t = 1" "(\<Sum>v\<in>t. u v *\<^sub>R v) = x"
```
```  1663   then show "\<exists>u. sum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = x"
```
```  1664     apply (rule_tac x="\<lambda>x. if x\<in>t then u x else 0" in exI)
```
```  1665     unfolding if_smult scaleR_zero_left and sum.inter_restrict[OF assms, symmetric] and *
```
```  1666     apply auto
```
```  1667     done
```
```  1668 qed
```
```  1669
```
```  1670
```
```  1671 subsubsection%unimportant \<open>Stepping theorems and hence small special cases\<close>
```
```  1672
```
```  1673 lemma affine_hull_empty[simp]: "affine hull {} = {}"
```
```  1674   by (rule hull_unique) auto
```
```  1675
```
```  1676 (*could delete: it simply rewrites sum expressions, but it's used twice*)
```
```  1677 lemma affine_hull_finite_step:
```
```  1678   fixes y :: "'a::real_vector"
```
```  1679   shows
```
```  1680     "(\<exists>u. sum u {} = w \<and> sum (\<lambda>x. u x *\<^sub>R x) {} = y) \<longleftrightarrow> w = 0 \<and> y = 0" (is ?th1)
```
```  1681     and
```
```  1682     "finite s \<Longrightarrow>
```
```  1683       (\<exists>u. sum u (insert a s) = w \<and> sum (\<lambda>x. u x *\<^sub>R x) (insert a s) = y) \<longleftrightarrow>
```
```  1684       (\<exists>v u. sum u s = w - v \<and> sum (\<lambda>x. u x *\<^sub>R x) s = y - v *\<^sub>R a)" (is "_ \<Longrightarrow> ?lhs = ?rhs")
```
```  1685 proof -
```
```  1686   show ?th1 by simp
```
```  1687   assume fin: "finite s"
```
```  1688   show "?lhs = ?rhs"
```
```  1689   proof
```
```  1690     assume ?lhs
```
```  1691     then obtain u where u: "sum u (insert a s) = w \<and> (\<Sum>x\<in>insert a s. u x *\<^sub>R x) = y"
```
```  1692       by auto
```
```  1693     show ?rhs
```
```  1694     proof (cases "a \<in> s")
```
```  1695       case True
```
```  1696       then have *: "insert a s = s" by auto
```
```  1697       show ?thesis
```
```  1698         using u[unfolded *]
```
```  1699         apply(rule_tac x=0 in exI)
```
```  1700         apply auto
```
```  1701         done
```
```  1702     next
```
```  1703       case False
```
```  1704       then show ?thesis
```
```  1705         apply (rule_tac x="u a" in exI)
```
```  1706         using u and fin
```
```  1707         apply auto
```
```  1708         done
```
```  1709     qed
```
```  1710   next
```
```  1711     assume ?rhs
```
```  1712     then obtain v u where vu: "sum u s = w - v"  "(\<Sum>x\<in>s. u x *\<^sub>R x) = y - v *\<^sub>R a"
```
```  1713       by auto
```
```  1714     have *: "\<And>x M. (if x = a then v else M) *\<^sub>R x = (if x = a then v *\<^sub>R x else M *\<^sub>R x)"
```
```  1715       by auto
```
```  1716     show ?lhs
```
```  1717     proof (cases "a \<in> s")
```
```  1718       case True
```
```  1719       then show ?thesis
```
```  1720         apply (rule_tac x="\<lambda>x. (if x=a then v else 0) + u x" in exI)
```
```  1721         unfolding sum_clauses(2)[OF fin]
```
```  1722         apply simp
```
```  1723         unfolding scaleR_left_distrib and sum.distrib
```
```  1724         unfolding vu and * and scaleR_zero_left
```
```  1725         apply (auto simp add: sum.delta[OF fin])
```
```  1726         done
```
```  1727     next
```
```  1728       case False
```
```  1729       then have **:
```
```  1730         "\<And>x. x \<in> s \<Longrightarrow> u x = (if x = a then v else u x)"
```
```  1731         "\<And>x. x \<in> s \<Longrightarrow> u x *\<^sub>R x = (if x = a then v *\<^sub>R x else u x *\<^sub>R x)" by auto
```
```  1732       from False show ?thesis
```
```  1733         apply (rule_tac x="\<lambda>x. if x=a then v else u x" in exI)
```
```  1734         unfolding sum_clauses(2)[OF fin] and * using vu
```
```  1735         using sum.cong [of s _ "\<lambda>x. u x *\<^sub>R x" "\<lambda>x. if x = a then v *\<^sub>R x else u x *\<^sub>R x", OF _ **(2)]
```
```  1736         using sum.cong [of s _ u "\<lambda>x. if x = a then v else u x", OF _ **(1)]
```
```  1737         apply auto
```
```  1738         done
```
```  1739     qed
```
```  1740   qed
```
```  1741 qed
```
```  1742
```
```  1743 lemma affine_hull_2:
```
```  1744   fixes a b :: "'a::real_vector"
```
```  1745   shows "affine hull {a,b} = {u *\<^sub>R a + v *\<^sub>R b| u v. (u + v = 1)}"
```
```  1746   (is "?lhs = ?rhs")
```
```  1747 proof -
```
```  1748   have *:
```
```  1749     "\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::real)"
```
```  1750     "\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::'a)" by auto
```
```  1751   have "?lhs = {y. \<exists>u. sum u {a, b} = 1 \<and> (\<Sum>v\<in>{a, b}. u v *\<^sub>R v) = y}"
```
```  1752     using affine_hull_finite[of "{a,b}"] by auto
```
```  1753   also have "\<dots> = {y. \<exists>v u. u b = 1 - v \<and> u b *\<^sub>R b = y - v *\<^sub>R a}"
```
```  1754     by (simp add: affine_hull_finite_step(2)[of "{b}" a])
```
```  1755   also have "\<dots> = ?rhs" unfolding * by auto
```
```  1756   finally show ?thesis by auto
```
```  1757 qed
```
```  1758
```
```  1759 lemma affine_hull_3:
```
```  1760   fixes a b c :: "'a::real_vector"
```
```  1761   shows "affine hull {a,b,c} = { u *\<^sub>R a + v *\<^sub>R b + w *\<^sub>R c| u v w. u + v + w = 1}"
```
```  1762 proof -
```
```  1763   have *:
```
```  1764     "\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::real)"
```
```  1765     "\<And>x y z. z = x - y \<longleftrightarrow> y + z = (x::'a)" by auto
```
```  1766   show ?thesis
```
```  1767     apply (simp add: affine_hull_finite affine_hull_finite_step)
```
```  1768     unfolding *
```
```  1769     apply auto
```
```  1770     apply (rule_tac x=v in exI)
```
```  1771     apply (rule_tac x=va in exI)
```
```  1772     apply auto
```
```  1773     apply (rule_tac x=u in exI)
```
```  1774     apply force
```
```  1775     done
```
```  1776 qed
```
```  1777
```
```  1778 lemma mem_affine:
```
```  1779   assumes "affine S" "x \<in> S" "y \<in> S" "u + v = 1"
```
```  1780   shows "u *\<^sub>R x + v *\<^sub>R y \<in> S"
```
```  1781   using assms affine_def[of S] by auto
```
```  1782
```
```  1783 lemma mem_affine_3:
```
```  1784   assumes "affine S" "x \<in> S" "y \<in> S" "z \<in> S" "u + v + w = 1"
```
```  1785   shows "u *\<^sub>R x + v *\<^sub>R y + w *\<^sub>R z \<in> S"
```
```  1786 proof -
```
```  1787   have "u *\<^sub>R x + v *\<^sub>R y + w *\<^sub>R z \<in> affine hull {x, y, z}"
```
```  1788     using affine_hull_3[of x y z] assms by auto
```
```  1789   moreover
```
```  1790   have "affine hull {x, y, z} \<subseteq> affine hull S"
```
```  1791     using hull_mono[of "{x, y, z}" "S"] assms by auto
```
```  1792   moreover
```
```  1793   have "affine hull S = S"
```
```  1794     using assms affine_hull_eq[of S] by auto
```
```  1795   ultimately show ?thesis by auto
```
```  1796 qed
```
```  1797
```
```  1798 lemma mem_affine_3_minus:
```
```  1799   assumes "affine S" "x \<in> S" "y \<in> S" "z \<in> S"
```
```  1800   shows "x + v *\<^sub>R (y-z) \<in> S"
```
```  1801   using mem_affine_3[of S x y z 1 v "-v"] assms
```
```  1802   by (simp add: algebra_simps)
```
```  1803
```
```  1804 corollary mem_affine_3_minus2:
```
```  1805     "\<lbrakk>affine S; x \<in> S; y \<in> S; z \<in> S\<rbrakk> \<Longrightarrow> x - v *\<^sub>R (y-z) \<in> S"
```
```  1806   by (metis add_uminus_conv_diff mem_affine_3_minus real_vector.scale_minus_left)
```
```  1807
```
```  1808
```
```  1809 subsubsection%unimportant \<open>Some relations between affine hull and subspaces\<close>
```
```  1810
```
```  1811 lemma affine_hull_insert_subset_span:
```
```  1812   "affine hull (insert a s) \<subseteq> {a + v| v . v \<in> span {x - a | x . x \<in> s}}"
```
```  1813   unfolding subset_eq Ball_def
```
```  1814   unfolding affine_hull_explicit span_explicit mem_Collect_eq
```
```  1815   apply (rule, rule)
```
```  1816   apply (erule exE)+
```
```  1817   apply (erule conjE)+
```
```  1818 proof -
```
```  1819   fix x t u
```
```  1820   assume as: "finite t" "t \<noteq> {}" "t \<subseteq> insert a s" "sum u t = 1" "(\<Sum>v\<in>t. u v *\<^sub>R v) = x"
```
```  1821   have "(\<lambda>x. x - a) ` (t - {a}) \<subseteq> {x - a |x. x \<in> s}"
```
```  1822     using as(3) by auto
```
```  1823   then show "\<exists>v. x = a + v \<and> (\<exists>S u. finite S \<and> S \<subseteq> {x - a |x. x \<in> s} \<and> (\<Sum>v\<in>S. u v *\<^sub>R v) = v)"
```
```  1824     apply (rule_tac x="x - a" in exI)
```
```  1825     apply (rule conjI, simp)
```
```  1826     apply (rule_tac x="(\<lambda>x. x - a) ` (t - {a})" in exI)
```
```  1827     apply (rule_tac x="\<lambda>x. u (x + a)" in exI)
```
```  1828     apply (rule conjI) using as(1) apply simp
```
```  1829     apply (erule conjI)
```
```  1830     using as(1)
```
```  1831     apply (simp add: sum.reindex[unfolded inj_on_def] scaleR_right_diff_distrib
```
```  1832       sum_subtractf scaleR_left.sum[symmetric] sum_diff1 scaleR_left_diff_distrib)
```
```  1833     unfolding as
```
```  1834     apply simp
```
```  1835     done
```
```  1836 qed
```
```  1837
```
```  1838 lemma affine_hull_insert_span:
```
```  1839   assumes "a \<notin> s"
```
```  1840   shows "affine hull (insert a s) = {a + v | v . v \<in> span {x - a | x.  x \<in> s}}"
```
```  1841   apply (rule, rule affine_hull_insert_subset_span)
```
```  1842   unfolding subset_eq Ball_def
```
```  1843   unfolding affine_hull_explicit and mem_Collect_eq
```
```  1844 proof (rule, rule, erule exE, erule conjE)
```
```  1845   fix y v
```
```  1846   assume "y = a + v" "v \<in> span {x - a |x. x \<in> s}"
```
```  1847   then obtain t u where obt: "finite t" "t \<subseteq> {x - a |x. x \<in> s}" "a + (\<Sum>v\<in>t. u v *\<^sub>R v) = y"
```
```  1848     unfolding span_explicit by auto
```
```  1849   define f where "f = (\<lambda>x. x + a) ` t"
```
```  1850   have f: "finite f" "f \<subseteq> s" "(\<Sum>v\<in>f. u (v - a) *\<^sub>R (v - a)) = y - a"
```
```  1851     unfolding f_def using obt by (auto simp add: sum.reindex[unfolded inj_on_def])
```
```  1852   have *: "f \<inter> {a} = {}" "f \<inter> - {a} = f"
```
```  1853     using f(2) assms by auto
```
```  1854   show "\<exists>sa u. finite sa \<and> sa \<noteq> {} \<and> sa \<subseteq> insert a s \<and> sum u sa = 1 \<and> (\<Sum>v\<in>sa. u v *\<^sub>R v) = y"
```
```  1855     apply (rule_tac x = "insert a f" in exI)
```
```  1856     apply (rule_tac x = "\<lambda>x. if x=a then 1 - sum (\<lambda>x. u (x - a)) f else u (x - a)" in exI)
```
```  1857     using assms and f
```
```  1858     unfolding sum_clauses(2)[OF f(1)] and if_smult
```
```  1859     unfolding sum.If_cases[OF f(1), of "\<lambda>x. x = a"]
```
```  1860     apply (auto simp add: sum_subtractf scaleR_left.sum algebra_simps *)
```
```  1861     done
```
```  1862 qed
```
```  1863
```
```  1864 lemma affine_hull_span:
```
```  1865   assumes "a \<in> s"
```
```  1866   shows "affine hull s = {a + v | v. v \<in> span {x - a | x. x \<in> s - {a}}}"
```
```  1867   using affine_hull_insert_span[of a "s - {a}", unfolded insert_Diff[OF assms]] by auto
```
```  1868
```
```  1869
```
```  1870 subsubsection%unimportant \<open>Parallel affine sets\<close>
```
```  1871
```
```  1872 definition affine_parallel :: "'a::real_vector set \<Rightarrow> 'a::real_vector set \<Rightarrow> bool"
```
```  1873   where "affine_parallel S T \<longleftrightarrow> (\<exists>a. T = (\<lambda>x. a + x) ` S)"
```
```  1874
```
```  1875 lemma affine_parallel_expl_aux:
```
```  1876   fixes S T :: "'a::real_vector set"
```
```  1877   assumes "\<forall>x. x \<in> S \<longleftrightarrow> a + x \<in> T"
```
```  1878   shows "T = (\<lambda>x. a + x) ` S"
```
```  1879 proof -
```
```  1880   {
```
```  1881     fix x
```
```  1882     assume "x \<in> T"
```
```  1883     then have "( - a) + x \<in> S"
```
```  1884       using assms by auto
```
```  1885     then have "x \<in> ((\<lambda>x. a + x) ` S)"
```
```  1886       using imageI[of "-a+x" S "(\<lambda>x. a+x)"] by auto
```
```  1887   }
```
```  1888   moreover have "T \<ge> (\<lambda>x. a + x) ` S"
```
```  1889     using assms by auto
```
```  1890   ultimately show ?thesis by auto
```
```  1891 qed
```
```  1892
```
```  1893 lemma affine_parallel_expl: "affine_parallel S T \<longleftrightarrow> (\<exists>a. \<forall>x. x \<in> S \<longleftrightarrow> a + x \<in> T)"
```
```  1894   unfolding affine_parallel_def
```
```  1895   using affine_parallel_expl_aux[of S _ T] by auto
```
```  1896
```
```  1897 lemma affine_parallel_reflex: "affine_parallel S S"
```
```  1898   unfolding affine_parallel_def
```
```  1899   apply (rule exI[of _ "0"])
```
```  1900   apply auto
```
```  1901   done
```
```  1902
```
```  1903 lemma affine_parallel_commut:
```
```  1904   assumes "affine_parallel A B"
```
```  1905   shows "affine_parallel B A"
```
```  1906 proof -
```
```  1907   from assms obtain a where B: "B = (\<lambda>x. a + x) ` A"
```
```  1908     unfolding affine_parallel_def by auto
```
```  1909   have [simp]: "(\<lambda>x. x - a) = plus (- a)" by (simp add: fun_eq_iff)
```
```  1910   from B show ?thesis
```
```  1911     using translation_galois [of B a A]
```
```  1912     unfolding affine_parallel_def by auto
```
```  1913 qed
```
```  1914
```
```  1915 lemma affine_parallel_assoc:
```
```  1916   assumes "affine_parallel A B"
```
```  1917     and "affine_parallel B C"
```
```  1918   shows "affine_parallel A C"
```
```  1919 proof -
```
```  1920   from assms obtain ab where "B = (\<lambda>x. ab + x) ` A"
```
```  1921     unfolding affine_parallel_def by auto
```
```  1922   moreover
```
```  1923   from assms obtain bc where "C = (\<lambda>x. bc + x) ` B"
```
```  1924     unfolding affine_parallel_def by auto
```
```  1925   ultimately show ?thesis
```
```  1926     using translation_assoc[of bc ab A] unfolding affine_parallel_def by auto
```
```  1927 qed
```
```  1928
```
```  1929 lemma affine_translation_aux:
```
```  1930   fixes a :: "'a::real_vector"
```
```  1931   assumes "affine ((\<lambda>x. a + x) ` S)"
```
```  1932   shows "affine S"
```
```  1933 proof -
```
```  1934   {
```
```  1935     fix x y u v
```
```  1936     assume xy: "x \<in> S" "y \<in> S" "(u :: real) + v = 1"
```
```  1937     then have "(a + x) \<in> ((\<lambda>x. a + x) ` S)" "(a + y) \<in> ((\<lambda>x. a + x) ` S)"
```
```  1938       by auto
```
```  1939     then have h1: "u *\<^sub>R  (a + x) + v *\<^sub>R (a + y) \<in> (\<lambda>x. a + x) ` S"
```
```  1940       using xy assms unfolding affine_def by auto
```
```  1941     have "u *\<^sub>R (a + x) + v *\<^sub>R (a + y) = (u + v) *\<^sub>R a + (u *\<^sub>R x + v *\<^sub>R y)"
```
```  1942       by (simp add: algebra_simps)
```
```  1943     also have "\<dots> = a + (u *\<^sub>R x + v *\<^sub>R y)"
```
```  1944       using \<open>u + v = 1\<close> by auto
```
```  1945     ultimately have "a + (u *\<^sub>R x + v *\<^sub>R y) \<in> (\<lambda>x. a + x) ` S"
```
```  1946       using h1 by auto
```
```  1947     then have "u *\<^sub>R x + v *\<^sub>R y \<in> S" by auto
```
```  1948   }
```
```  1949   then show ?thesis unfolding affine_def by auto
```
```  1950 qed
```
```  1951
```
```  1952 lemma affine_translation:
```
```  1953   fixes a :: "'a::real_vector"
```
```  1954   shows "affine S \<longleftrightarrow> affine ((\<lambda>x. a + x) ` S)"
```
```  1955 proof -
```
```  1956   have "affine S \<Longrightarrow> affine ((\<lambda>x. a + x) ` S)"
```
```  1957     using affine_translation_aux[of "-a" "((\<lambda>x. a + x) ` S)"]
```
```  1958     using translation_assoc[of "-a" a S] by auto
```
```  1959   then show ?thesis using affine_translation_aux by auto
```
```  1960 qed
```
```  1961
```
```  1962 lemma parallel_is_affine:
```
```  1963   fixes S T :: "'a::real_vector set"
```
```  1964   assumes "affine S" "affine_parallel S T"
```
```  1965   shows "affine T"
```
```  1966 proof -
```
```  1967   from assms obtain a where "T = (\<lambda>x. a + x) ` S"
```
```  1968     unfolding affine_parallel_def by auto
```
```  1969   then show ?thesis
```
```  1970     using affine_translation assms by auto
```
```  1971 qed
```
```  1972
```
```  1973 lemma subspace_imp_affine: "subspace s \<Longrightarrow> affine s"
```
```  1974   unfolding subspace_def affine_def by auto
```
```  1975
```
```  1976
```
```  1977 subsubsection%unimportant \<open>Subspace parallel to an affine set\<close>
```
```  1978
```
```  1979 lemma subspace_affine: "subspace S \<longleftrightarrow> affine S \<and> 0 \<in> S"
```
```  1980 proof -
```
```  1981   have h0: "subspace S \<Longrightarrow> affine S \<and> 0 \<in> S"
```
```  1982     using subspace_imp_affine[of S] subspace_0 by auto
```
```  1983   {
```
```  1984     assume assm: "affine S \<and> 0 \<in> S"
```
```  1985     {
```
```  1986       fix c :: real
```
```  1987       fix x
```
```  1988       assume x: "x \<in> S"
```
```  1989       have "c *\<^sub>R x = (1-c) *\<^sub>R 0 + c *\<^sub>R x" by auto
```
```  1990       moreover
```
```  1991       have "(1 - c) *\<^sub>R 0 + c *\<^sub>R x \<in> S"
```
```  1992         using affine_alt[of S] assm x by auto
```
```  1993       ultimately have "c *\<^sub>R x \<in> S" by auto
```
```  1994     }
```
```  1995     then have h1: "\<forall>c. \<forall>x \<in> S. c *\<^sub>R x \<in> S" by auto
```
```  1996
```
```  1997     {
```
```  1998       fix x y
```
```  1999       assume xy: "x \<in> S" "y \<in> S"
```
```  2000       define u where "u = (1 :: real)/2"
```
```  2001       have "(1/2) *\<^sub>R (x+y) = (1/2) *\<^sub>R (x+y)"
```
```  2002         by auto
```
```  2003       moreover
```
```  2004       have "(1/2) *\<^sub>R (x+y)=(1/2) *\<^sub>R x + (1-(1/2)) *\<^sub>R y"
```
```  2005         by (simp add: algebra_simps)
```
```  2006       moreover
```
```  2007       have "(1 - u) *\<^sub>R x + u *\<^sub>R y \<in> S"
```
```  2008         using affine_alt[of S] assm xy by auto
```
```  2009       ultimately
```
```  2010       have "(1/2) *\<^sub>R (x+y) \<in> S"
```
```  2011         using u_def by auto
```
```  2012       moreover
```
```  2013       have "x + y = 2 *\<^sub>R ((1/2) *\<^sub>R (x+y))"
```
```  2014         by auto
```
```  2015       ultimately
```
```  2016       have "x + y \<in> S"
```
```  2017         using h1[rule_format, of "(1/2) *\<^sub>R (x+y)" "2"] by auto
```
```  2018     }
```
```  2019     then have "\<forall>x \<in> S. \<forall>y \<in> S. x + y \<in> S"
```
```  2020       by auto
```
```  2021     then have "subspace S"
```
```  2022       using h1 assm unfolding subspace_def by auto
```
```  2023   }
```
```  2024   then show ?thesis using h0 by metis
```
```  2025 qed
```
```  2026
```
```  2027 lemma affine_diffs_subspace:
```
```  2028   assumes "affine S" "a \<in> S"
```
```  2029   shows "subspace ((\<lambda>x. (-a)+x) ` S)"
```
```  2030 proof -
```
```  2031   have [simp]: "(\<lambda>x. x - a) = plus (- a)" by (simp add: fun_eq_iff)
```
```  2032   have "affine ((\<lambda>x. (-a)+x) ` S)"
```
```  2033     using  affine_translation assms by auto
```
```  2034   moreover have "0 \<in> ((\<lambda>x. (-a)+x) ` S)"
```
```  2035     using assms exI[of "(\<lambda>x. x\<in>S \<and> -a+x = 0)" a] by auto
```
```  2036   ultimately show ?thesis using subspace_affine by auto
```
```  2037 qed
```
```  2038
```
```  2039 lemma parallel_subspace_explicit:
```
```  2040   assumes "affine S"
```
```  2041     and "a \<in> S"
```
```  2042   assumes "L \<equiv> {y. \<exists>x \<in> S. (-a) + x = y}"
```
```  2043   shows "subspace L \<and> affine_parallel S L"
```
```  2044 proof -
```
```  2045   from assms have "L = plus (- a) ` S" by auto
```
```  2046   then have par: "affine_parallel S L"
```
```  2047     unfolding affine_parallel_def ..
```
```  2048   then have "affine L" using assms parallel_is_affine by auto
```
```  2049   moreover have "0 \<in> L"
```
```  2050     using assms by auto
```
```  2051   ultimately show ?thesis
```
```  2052     using subspace_affine par by auto
```
```  2053 qed
```
```  2054
```
```  2055 lemma parallel_subspace_aux:
```
```  2056   assumes "subspace A"
```
```  2057     and "subspace B"
```
```  2058     and "affine_parallel A B"
```
```  2059   shows "A \<supseteq> B"
```
```  2060 proof -
```
```  2061   from assms obtain a where a: "\<forall>x. x \<in> A \<longleftrightarrow> a + x \<in> B"
```
```  2062     using affine_parallel_expl[of A B] by auto
```
```  2063   then have "-a \<in> A"
```
```  2064     using assms subspace_0[of B] by auto
```
```  2065   then have "a \<in> A"
```
```  2066     using assms subspace_neg[of A "-a"] by auto
```
```  2067   then show ?thesis
```
```  2068     using assms a unfolding subspace_def by auto
```
```  2069 qed
```
```  2070
```
```  2071 lemma parallel_subspace:
```
```  2072   assumes "subspace A"
```
```  2073     and "subspace B"
```
```  2074     and "affine_parallel A B"
```
```  2075   shows "A = B"
```
```  2076 proof
```
```  2077   show "A \<supseteq> B"
```
```  2078     using assms parallel_subspace_aux by auto
```
```  2079   show "A \<subseteq> B"
```
```  2080     using assms parallel_subspace_aux[of B A] affine_parallel_commut by auto
```
```  2081 qed
```
```  2082
```
```  2083 lemma affine_parallel_subspace:
```
```  2084   assumes "affine S" "S \<noteq> {}"
```
```  2085   shows "\<exists>!L. subspace L \<and> affine_parallel S L"
```
```  2086 proof -
```
```  2087   have ex: "\<exists>L. subspace L \<and> affine_parallel S L"
```
```  2088     using assms parallel_subspace_explicit by auto
```
```  2089   {
```
```  2090     fix L1 L2
```
```  2091     assume ass: "subspace L1 \<and> affine_parallel S L1" "subspace L2 \<and> affine_parallel S L2"
```
```  2092     then have "affine_parallel L1 L2"
```
```  2093       using affine_parallel_commut[of S L1] affine_parallel_assoc[of L1 S L2] by auto
```
```  2094     then have "L1 = L2"
```
```  2095       using ass parallel_subspace by auto
```
```  2096   }
```
```  2097   then show ?thesis using ex by auto
```
```  2098 qed
```
```  2099
```
```  2100
```
```  2101 subsection \<open>Cones\<close>
```
```  2102
```
```  2103 definition%important cone :: "'a::real_vector set \<Rightarrow> bool"
```
```  2104   where "cone s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>c\<ge>0. c *\<^sub>R x \<in> s)"
```
```  2105
```
```  2106 lemma cone_empty[intro, simp]: "cone {}"
```
```  2107   unfolding cone_def by auto
```
```  2108
```
```  2109 lemma cone_univ[intro, simp]: "cone UNIV"
```
```  2110   unfolding cone_def by auto
```
```  2111
```
```  2112 lemma cone_Inter[intro]: "\<forall>s\<in>f. cone s \<Longrightarrow> cone (\<Inter>f)"
```
```  2113   unfolding cone_def by auto
```
```  2114
```
```  2115 lemma subspace_imp_cone: "subspace S \<Longrightarrow> cone S"
```
```  2116   by (simp add: cone_def subspace_mul)
```
```  2117
```
```  2118
```
```  2119 subsubsection \<open>Conic hull\<close>
```
```  2120
```
```  2121 lemma cone_cone_hull: "cone (cone hull s)"
```
```  2122   unfolding hull_def by auto
```
```  2123
```
```  2124 lemma cone_hull_eq: "cone hull s = s \<longleftrightarrow> cone s"
```
```  2125   apply (rule hull_eq)
```
```  2126   using cone_Inter
```
```  2127   unfolding subset_eq
```
```  2128   apply auto
```
```  2129   done
```
```  2130
```
```  2131 lemma mem_cone:
```
```  2132   assumes "cone S" "x \<in> S" "c \<ge> 0"
```
```  2133   shows "c *\<^sub>R x \<in> S"
```
```  2134   using assms cone_def[of S] by auto
```
```  2135
```
```  2136 lemma cone_contains_0:
```
```  2137   assumes "cone S"
```
```  2138   shows "S \<noteq> {} \<longleftrightarrow> 0 \<in> S"
```
```  2139 proof -
```
```  2140   {
```
```  2141     assume "S \<noteq> {}"
```
```  2142     then obtain a where "a \<in> S" by auto
```
```  2143     then have "0 \<in> S"
```
```  2144       using assms mem_cone[of S a 0] by auto
```
```  2145   }
```
```  2146   then show ?thesis by auto
```
```  2147 qed
```
```  2148
```
```  2149 lemma cone_0: "cone {0}"
```
```  2150   unfolding cone_def by auto
```
```  2151
```
```  2152 lemma cone_Union[intro]: "(\<forall>s\<in>f. cone s) \<longrightarrow> cone (\<Union>f)"
```
```  2153   unfolding cone_def by blast
```
```  2154
```
```  2155 lemma cone_iff:
```
```  2156   assumes "S \<noteq> {}"
```
```  2157   shows "cone S \<longleftrightarrow> 0 \<in> S \<and> (\<forall>c. c > 0 \<longrightarrow> (( *\<^sub>R) c) ` S = S)"
```
```  2158 proof -
```
```  2159   {
```
```  2160     assume "cone S"
```
```  2161     {
```
```  2162       fix c :: real
```
```  2163       assume "c > 0"
```
```  2164       {
```
```  2165         fix x
```
```  2166         assume "x \<in> S"
```
```  2167         then have "x \<in> (( *\<^sub>R) c) ` S"
```
```  2168           unfolding image_def
```
```  2169           using \<open>cone S\<close> \<open>c>0\<close> mem_cone[of S x "1/c"]
```
```  2170             exI[of "(\<lambda>t. t \<in> S \<and> x = c *\<^sub>R t)" "(1 / c) *\<^sub>R x"]
```
```  2171           by auto
```
```  2172       }
```
```  2173       moreover
```
```  2174       {
```
```  2175         fix x
```
```  2176         assume "x \<in> (( *\<^sub>R) c) ` S"
```
```  2177         then have "x \<in> S"
```
```  2178           using \<open>cone S\<close> \<open>c > 0\<close>
```
```  2179           unfolding cone_def image_def \<open>c > 0\<close> by auto
```
```  2180       }
```
```  2181       ultimately have "(( *\<^sub>R) c) ` S = S" by auto
```
```  2182     }
```
```  2183     then have "0 \<in> S \<and> (\<forall>c. c > 0 \<longrightarrow> (( *\<^sub>R) c) ` S = S)"
```
```  2184       using \<open>cone S\<close> cone_contains_0[of S] assms by auto
```
```  2185   }
```
```  2186   moreover
```
```  2187   {
```
```  2188     assume a: "0 \<in> S \<and> (\<forall>c. c > 0 \<longrightarrow> (( *\<^sub>R) c) ` S = S)"
```
```  2189     {
```
```  2190       fix x
```
```  2191       assume "x \<in> S"
```
```  2192       fix c1 :: real
```
```  2193       assume "c1 \<ge> 0"
```
```  2194       then have "c1 = 0 \<or> c1 > 0" by auto
```
```  2195       then have "c1 *\<^sub>R x \<in> S" using a \<open>x \<in> S\<close> by auto
```
```  2196     }
```
```  2197     then have "cone S" unfolding cone_def by auto
```
```  2198   }
```
```  2199   ultimately show ?thesis by blast
```
```  2200 qed
```
```  2201
```
```  2202 lemma cone_hull_empty: "cone hull {} = {}"
```
```  2203   by (metis cone_empty cone_hull_eq)
```
```  2204
```
```  2205 lemma cone_hull_empty_iff: "S = {} \<longleftrightarrow> cone hull S = {}"
```
```  2206   by (metis bot_least cone_hull_empty hull_subset xtrans(5))
```
```  2207
```
```  2208 lemma cone_hull_contains_0: "S \<noteq> {} \<longleftrightarrow> 0 \<in> cone hull S"
```
```  2209   using cone_cone_hull[of S] cone_contains_0[of "cone hull S"] cone_hull_empty_iff[of S]
```
```  2210   by auto
```
```  2211
```
```  2212 lemma mem_cone_hull:
```
```  2213   assumes "x \<in> S" "c \<ge> 0"
```
```  2214   shows "c *\<^sub>R x \<in> cone hull S"
```
```  2215   by (metis assms cone_cone_hull hull_inc mem_cone)
```
```  2216
```
```  2217 lemma%important cone_hull_expl: "cone hull S = {c *\<^sub>R x | c x. c \<ge> 0 \<and> x \<in> S}"
```
```  2218   (is "?lhs = ?rhs")
```
```  2219 proof%unimportant -
```
```  2220   {
```
```  2221     fix x
```
```  2222     assume "x \<in> ?rhs"
```
```  2223     then obtain cx :: real and xx where x: "x = cx *\<^sub>R xx" "cx \<ge> 0" "xx \<in> S"
```
```  2224       by auto
```
```  2225     fix c :: real
```
```  2226     assume c: "c \<ge> 0"
```
```  2227     then have "c *\<^sub>R x = (c * cx) *\<^sub>R xx"
```
```  2228       using x by (simp add: algebra_simps)
```
```  2229     moreover
```
```  2230     have "c * cx \<ge> 0" using c x by auto
```
```  2231     ultimately
```
```  2232     have "c *\<^sub>R x \<in> ?rhs" using x by auto
```
```  2233   }
```
```  2234   then have "cone ?rhs"
```
```  2235     unfolding cone_def by auto
```
```  2236   then have "?rhs \<in> Collect cone"
```
```  2237     unfolding mem_Collect_eq by auto
```
```  2238   {
```
```  2239     fix x
```
```  2240     assume "x \<in> S"
```
```  2241     then have "1 *\<^sub>R x \<in> ?rhs"
```
```  2242       apply auto
```
```  2243       apply (rule_tac x = 1 in exI)
```
```  2244       apply auto
```
```  2245       done
```
```  2246     then have "x \<in> ?rhs" by auto
```
```  2247   }
```
```  2248   then have "S \<subseteq> ?rhs" by auto
```
```  2249   then have "?lhs \<subseteq> ?rhs"
```
```  2250     using \<open>?rhs \<in> Collect cone\<close> hull_minimal[of S "?rhs" "cone"] by auto
```
```  2251   moreover
```
```  2252   {
```
```  2253     fix x
```
```  2254     assume "x \<in> ?rhs"
```
```  2255     then obtain cx :: real and xx where x: "x = cx *\<^sub>R xx" "cx \<ge> 0" "xx \<in> S"
```
```  2256       by auto
```
```  2257     then have "xx \<in> cone hull S"
```
```  2258       using hull_subset[of S] by auto
```
```  2259     then have "x \<in> ?lhs"
```
```  2260       using x cone_cone_hull[of S] cone_def[of "cone hull S"] by auto
```
```  2261   }
```
```  2262   ultimately show ?thesis by auto
```
```  2263 qed
```
```  2264
```
```  2265 lemma cone_closure:
```
```  2266   fixes S :: "'a::real_normed_vector set"
```
```  2267   assumes "cone S"
```
```  2268   shows "cone (closure S)"
```
```  2269 proof (cases "S = {}")
```
```  2270   case True
```
```  2271   then show ?thesis by auto
```
```  2272 next
```
```  2273   case False
```
```  2274   then have "0 \<in> S \<and> (\<forall>c. c > 0 \<longrightarrow> ( *\<^sub>R) c ` S = S)"
```
```  2275     using cone_iff[of S] assms by auto
```
```  2276   then have "0 \<in> closure S \<and> (\<forall>c. c > 0 \<longrightarrow> ( *\<^sub>R) c ` closure S = closure S)"
```
```  2277     using closure_subset by (auto simp add: closure_scaleR)
```
```  2278   then show ?thesis
```
```  2279     using False cone_iff[of "closure S"] by auto
```
```  2280 qed
```
```  2281
```
```  2282
```
```  2283 subsection \<open>Affine dependence and consequential theorems (from Lars Schewe)\<close>
```
```  2284
```
```  2285 definition%important affine_dependent :: "'a::real_vector set \<Rightarrow> bool"
```
```  2286   where "affine_dependent s \<longleftrightarrow> (\<exists>x\<in>s. x \<in> affine hull (s - {x}))"
```
```  2287
```
```  2288 lemma affine_dependent_subset:
```
```  2289    "\<lbrakk>affine_dependent s; s \<subseteq> t\<rbrakk> \<Longrightarrow> affine_dependent t"
```
```  2290 apply (simp add: affine_dependent_def Bex_def)
```
```  2291 apply (blast dest: hull_mono [OF Diff_mono [OF _ subset_refl]])
```
```  2292 done
```
```  2293
```
```  2294 lemma affine_independent_subset:
```
```  2295   shows "\<lbrakk>~ affine_dependent t; s \<subseteq> t\<rbrakk> \<Longrightarrow> ~ affine_dependent s"
```
```  2296 by (metis affine_dependent_subset)
```
```  2297
```
```  2298 lemma affine_independent_Diff:
```
```  2299    "~ affine_dependent s \<Longrightarrow> ~ affine_dependent(s - t)"
```
```  2300 by (meson Diff_subset affine_dependent_subset)
```
```  2301
```
```  2302 lemma%important affine_dependent_explicit:
```
```  2303   "affine_dependent p \<longleftrightarrow>
```
```  2304     (\<exists>s u. finite s \<and> s \<subseteq> p \<and> sum u s = 0 \<and>
```
```  2305       (\<exists>v\<in>s. u v \<noteq> 0) \<and> sum (\<lambda>v. u v *\<^sub>R v) s = 0)"
```
```  2306   unfolding%unimportant affine_dependent_def affine_hull_explicit mem_Collect_eq
```
```  2307   apply rule
```
```  2308   apply (erule bexE, erule exE, erule exE)
```
```  2309   apply (erule conjE)+
```
```  2310   defer
```
```  2311   apply (erule exE, erule exE)
```
```  2312   apply (erule conjE)+
```
```  2313   apply (erule bexE)
```
```  2314 proof -
```
```  2315   fix x s u
```
```  2316   assume as: "x \<in> p" "finite s" "s \<noteq> {}" "s \<subseteq> p - {x}" "sum u s = 1" "(\<Sum>v\<in>s. u v *\<^sub>R v) = x"
```
```  2317   have "x \<notin> s" using as(1,4) by auto
```
```  2318   show "\<exists>s u. finite s \<and> s \<subseteq> p \<and> sum u s = 0 \<and> (\<exists>v\<in>s. u v \<noteq> 0) \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = 0"
```
```  2319     apply (rule_tac x="insert x s" in exI, rule_tac x="\<lambda>v. if v = x then - 1 else u v" in exI)
```
```  2320     unfolding if_smult and sum_clauses(2)[OF as(2)] and sum_delta_notmem[OF \<open>x\<notin>s\<close>] and as
```
```  2321     using as
```
```  2322     apply auto
```
```  2323     done
```
```  2324 next
```
```  2325   fix s u v
```
```  2326   assume as: "finite s" "s \<subseteq> p" "sum u s = 0" "(\<Sum>v\<in>s. u v *\<^sub>R v) = 0" "v \<in> s" "u v \<noteq> 0"
```
```  2327   have "s \<noteq> {v}"
```
```  2328     using as(3,6) by auto
```
```  2329   then show "\<exists>x\<in>p. \<exists>s u. finite s \<and> s \<noteq> {} \<and> s \<subseteq> p - {x} \<and> sum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = x"
```
```  2330     apply (rule_tac x=v in bexI)
```
```  2331     apply (rule_tac x="s - {v}" in exI)
```
```  2332     apply (rule_tac x="\<lambda>x. - (1 / u v) * u x" in exI)
```
```  2333     unfolding scaleR_scaleR[symmetric] and scaleR_right.sum [symmetric]
```
```  2334     unfolding sum_distrib_left[symmetric] and sum_diff1[OF as(1)]
```
```  2335     using as
```
```  2336     apply auto
```
```  2337     done
```
```  2338 qed
```
```  2339
```
```  2340 lemma affine_dependent_explicit_finite:
```
```  2341   fixes s :: "'a::real_vector set"
```
```  2342   assumes "finite s"
```
```  2343   shows "affine_dependent s \<longleftrightarrow>
```
```  2344     (\<exists>u. sum u s = 0 \<and> (\<exists>v\<in>s. u v \<noteq> 0) \<and> sum (\<lambda>v. u v *\<^sub>R v) s = 0)"
```
```  2345   (is "?lhs = ?rhs")
```
```  2346 proof
```
```  2347   have *: "\<And>vt u v. (if vt then u v else 0) *\<^sub>R v = (if vt then (u v) *\<^sub>R v else 0::'a)"
```
```  2348     by auto
```
```  2349   assume ?lhs
```
```  2350   then obtain t u v where
```
```  2351     "finite t" "t \<subseteq> s" "sum u t = 0" "v\<in>t" "u v \<noteq> 0"  "(\<Sum>v\<in>t. u v *\<^sub>R v) = 0"
```
```  2352     unfolding affine_dependent_explicit by auto
```
```  2353   then show ?rhs
```
```  2354     apply (rule_tac x="\<lambda>x. if x\<in>t then u x else 0" in exI)
```
```  2355     apply auto unfolding * and sum.inter_restrict[OF assms, symmetric]
```
```  2356     unfolding Int_absorb1[OF \<open>t\<subseteq>s\<close>]
```
```  2357     apply auto
```
```  2358     done
```
```  2359 next
```
```  2360   assume ?rhs
```
```  2361   then obtain u v where "sum u s = 0"  "v\<in>s" "u v \<noteq> 0" "(\<Sum>v\<in>s. u v *\<^sub>R v) = 0"
```
```  2362     by auto
```
```  2363   then show ?lhs unfolding affine_dependent_explicit
```
```  2364     using assms by auto
```
```  2365 qed
```
```  2366
```
```  2367
```
```  2368 subsection%unimportant \<open>Connectedness of convex sets\<close>
```
```  2369
```
```  2370 lemma connectedD:
```
```  2371   "connected S \<Longrightarrow> open A \<Longrightarrow> open B \<Longrightarrow> S \<subseteq> A \<union> B \<Longrightarrow> A \<inter> B \<inter> S = {} \<Longrightarrow> A \<inter> S = {} \<or> B \<inter> S = {}"
```
```  2372   by (rule Topological_Spaces.topological_space_class.connectedD)
```
```  2373
```
```  2374 lemma convex_connected:
```
```  2375   fixes s :: "'a::real_normed_vector set"
```
```  2376   assumes "convex s"
```
```  2377   shows "connected s"
```
```  2378 proof (rule connectedI)
```
```  2379   fix A B
```
```  2380   assume "open A" "open B" "A \<inter> B \<inter> s = {}" "s \<subseteq> A \<union> B"
```
```  2381   moreover
```
```  2382   assume "A \<inter> s \<noteq> {}" "B \<inter> s \<noteq> {}"
```
```  2383   then obtain a b where a: "a \<in> A" "a \<in> s" and b: "b \<in> B" "b \<in> s" by auto
```
```  2384   define f where [abs_def]: "f u = u *\<^sub>R a + (1 - u) *\<^sub>R b" for u
```
```  2385   then have "continuous_on {0 .. 1} f"
```
```  2386     by (auto intro!: continuous_intros)
```
```  2387   then have "connected (f ` {0 .. 1})"
```
```  2388     by (auto intro!: connected_continuous_image)
```
```  2389   note connectedD[OF this, of A B]
```
```  2390   moreover have "a \<in> A \<inter> f ` {0 .. 1}"
```
```  2391     using a by (auto intro!: image_eqI[of _ _ 1] simp: f_def)
```
```  2392   moreover have "b \<in> B \<inter> f ` {0 .. 1}"
```
```  2393     using b by (auto intro!: image_eqI[of _ _ 0] simp: f_def)
```
```  2394   moreover have "f ` {0 .. 1} \<subseteq> s"
```
```  2395     using \<open>convex s\<close> a b unfolding convex_def f_def by auto
```
```  2396   ultimately show False by auto
```
```  2397 qed
```
```  2398
```
```  2399 corollary connected_UNIV[intro]: "connected (UNIV :: 'a::real_normed_vector set)"
```
```  2400   by (simp add: convex_connected)
```
```  2401
```
```  2402 corollary component_complement_connected:
```
```  2403   fixes S :: "'a::real_normed_vector set"
```
```  2404   assumes "connected S" "C \<in> components (-S)"
```
```  2405   shows "connected(-C)"
```
```  2406   using component_diff_connected [of S UNIV] assms
```
```  2407   by (auto simp: Compl_eq_Diff_UNIV)
```
```  2408
```
```  2409 proposition clopen:
```
```  2410   fixes S :: "'a :: real_normed_vector set"
```
```  2411   shows "closed S \<and> open S \<longleftrightarrow> S = {} \<or> S = UNIV"
```
```  2412     by (force intro!: connected_UNIV [unfolded connected_clopen, rule_format])
```
```  2413
```
```  2414 corollary compact_open:
```
```  2415   fixes S :: "'a :: euclidean_space set"
```
```  2416   shows "compact S \<and> open S \<longleftrightarrow> S = {}"
```
```  2417   by (auto simp: compact_eq_bounded_closed clopen)
```
```  2418
```
```  2419 corollary finite_imp_not_open:
```
```  2420     fixes S :: "'a::{real_normed_vector, perfect_space} set"
```
```  2421     shows "\<lbrakk>finite S; open S\<rbrakk> \<Longrightarrow> S={}"
```
```  2422   using clopen [of S] finite_imp_closed not_bounded_UNIV by blast
```
```  2423
```
```  2424 corollary empty_interior_finite:
```
```  2425     fixes S :: "'a::{real_normed_vector, perfect_space} set"
```
```  2426     shows "finite S \<Longrightarrow> interior S = {}"
```
```  2427   by (metis interior_subset finite_subset open_interior [of S] finite_imp_not_open)
```
```  2428
```
```  2429 text \<open>Balls, being convex, are connected.\<close>
```
```  2430
```
```  2431 lemma convex_prod:
```
```  2432   assumes "\<And>i. i \<in> Basis \<Longrightarrow> convex {x. P i x}"
```
```  2433   shows "convex {x. \<forall>i\<in>Basis. P i (x\<bullet>i)}"
```
```  2434   using assms unfolding convex_def
```
```  2435   by (auto simp: inner_add_left)
```
```  2436
```
```  2437 lemma convex_positive_orthant: "convex {x::'a::euclidean_space. (\<forall>i\<in>Basis. 0 \<le> x\<bullet>i)}"
```
```  2438   by (rule convex_prod) (simp add: atLeast_def[symmetric] convex_real_interval)
```
```  2439
```
```  2440 lemma convex_local_global_minimum:
```
```  2441   fixes s :: "'a::real_normed_vector set"
```
```  2442   assumes "e > 0"
```
```  2443     and "convex_on s f"
```
```  2444     and "ball x e \<subseteq> s"
```
```  2445     and "\<forall>y\<in>ball x e. f x \<le> f y"
```
```  2446   shows "\<forall>y\<in>s. f x \<le> f y"
```
```  2447 proof (rule ccontr)
```
```  2448   have "x \<in> s" using assms(1,3) by auto
```
```  2449   assume "\<not> ?thesis"
```
```  2450   then obtain y where "y\<in>s" and y: "f x > f y" by auto
```
```  2451   then have xy: "0 < dist x y"  by auto
```
```  2452   then obtain u where "0 < u" "u \<le> 1" and u: "u < e / dist x y"
```
```  2453     using real_lbound_gt_zero[of 1 "e / dist x y"] xy \<open>e>0\<close> by auto
```
```  2454   then have "f ((1-u) *\<^sub>R x + u *\<^sub>R y) \<le> (1-u) * f x + u * f y"
```
```  2455     using \<open>x\<in>s\<close> \<open>y\<in>s\<close>
```
```  2456     using assms(2)[unfolded convex_on_def,
```
```  2457       THEN bspec[where x=x], THEN bspec[where x=y], THEN spec[where x="1-u"]]
```
```  2458     by auto
```
```  2459   moreover
```
```  2460   have *: "x - ((1 - u) *\<^sub>R x + u *\<^sub>R y) = u *\<^sub>R (x - y)"
```
```  2461     by (simp add: algebra_simps)
```
```  2462   have "(1 - u) *\<^sub>R x + u *\<^sub>R y \<in> ball x e"
```
```  2463     unfolding mem_ball dist_norm
```
```  2464     unfolding * and norm_scaleR and abs_of_pos[OF \<open>0<u\<close>]
```
```  2465     unfolding dist_norm[symmetric]
```
```  2466     using u
```
```  2467     unfolding pos_less_divide_eq[OF xy]
```
```  2468     by auto
```
```  2469   then have "f x \<le> f ((1 - u) *\<^sub>R x + u *\<^sub>R y)"
```
```  2470     using assms(4) by auto
```
```  2471   ultimately show False
```
```  2472     using mult_strict_left_mono[OF y \<open>u>0\<close>]
```
```  2473     unfolding left_diff_distrib
```
```  2474     by auto
```
```  2475 qed
```
```  2476
```
```  2477 lemma convex_ball [iff]:
```
```  2478   fixes x :: "'a::real_normed_vector"
```
```  2479   shows "convex (ball x e)"
```
```  2480 proof (auto simp add: convex_def)
```
```  2481   fix y z
```
```  2482   assume yz: "dist x y < e" "dist x z < e"
```
```  2483   fix u v :: real
```
```  2484   assume uv: "0 \<le> u" "0 \<le> v" "u + v = 1"
```
```  2485   have "dist x (u *\<^sub>R y + v *\<^sub>R z) \<le> u * dist x y + v * dist x z"
```
```  2486     using uv yz
```
```  2487     using convex_on_dist [of "ball x e" x, unfolded convex_on_def,
```
```  2488       THEN bspec[where x=y], THEN bspec[where x=z]]
```
```  2489     by auto
```
```  2490   then show "dist x (u *\<^sub>R y + v *\<^sub>R z) < e"
```
```  2491     using convex_bound_lt[OF yz uv] by auto
```
```  2492 qed
```
```  2493
```
```  2494 lemma convex_cball [iff]:
```
```  2495   fixes x :: "'a::real_normed_vector"
```
```  2496   shows "convex (cball x e)"
```
```  2497 proof -
```
```  2498   {
```
```  2499     fix y z
```
```  2500     assume yz: "dist x y \<le> e" "dist x z \<le> e"
```
```  2501     fix u v :: real
```
```  2502     assume uv: "0 \<le> u" "0 \<le> v" "u + v = 1"
```
```  2503     have "dist x (u *\<^sub>R y + v *\<^sub>R z) \<le> u * dist x y + v * dist x z"
```
```  2504       using uv yz
```
```  2505       using convex_on_dist [of "cball x e" x, unfolded convex_on_def,
```
```  2506         THEN bspec[where x=y], THEN bspec[where x=z]]
```
```  2507       by auto
```
```  2508     then have "dist x (u *\<^sub>R y + v *\<^sub>R z) \<le> e"
```
```  2509       using convex_bound_le[OF yz uv] by auto
```
```  2510   }
```
```  2511   then show ?thesis by (auto simp add: convex_def Ball_def)
```
```  2512 qed
```
```  2513
```
```  2514 lemma connected_ball [iff]:
```
```  2515   fixes x :: "'a::real_normed_vector"
```
```  2516   shows "connected (ball x e)"
```
```  2517   using convex_connected convex_ball by auto
```
```  2518
```
```  2519 lemma connected_cball [iff]:
```
```  2520   fixes x :: "'a::real_normed_vector"
```
```  2521   shows "connected (cball x e)"
```
```  2522   using convex_connected convex_cball by auto
```
```  2523
```
```  2524
```
```  2525 subsection \<open>Convex hull\<close>
```
```  2526
```
```  2527 lemma convex_convex_hull [iff]: "convex (convex hull s)"
```
```  2528   unfolding hull_def
```
```  2529   using convex_Inter[of "{t. convex t \<and> s \<subseteq> t}"]
```
```  2530   by auto
```
```  2531
```
```  2532 lemma convex_hull_subset:
```
```  2533     "s \<subseteq> convex hull t \<Longrightarrow> convex hull s \<subseteq> convex hull t"
```
```  2534   by (simp add: convex_convex_hull subset_hull)
```
```  2535
```
```  2536 lemma convex_hull_eq: "convex hull s = s \<longleftrightarrow> convex s"
```
```  2537   by (metis convex_convex_hull hull_same)
```
```  2538
```
```  2539 lemma bounded_convex_hull:
```
```  2540   fixes s :: "'a::real_normed_vector set"
```
```  2541   assumes "bounded s"
```
```  2542   shows "bounded (convex hull s)"
```
```  2543 proof -
```
```  2544   from assms obtain B where B: "\<forall>x\<in>s. norm x \<le> B"
```
```  2545     unfolding bounded_iff by auto
```
```  2546   show ?thesis
```
```  2547     apply (rule bounded_subset[OF bounded_cball, of _ 0 B])
```
```  2548     unfolding subset_hull[of convex, OF convex_cball]
```
```  2549     unfolding subset_eq mem_cball dist_norm using B
```
```  2550     apply auto
```
```  2551     done
```
```  2552 qed
```
```  2553
```
```  2554 lemma finite_imp_bounded_convex_hull:
```
```  2555   fixes s :: "'a::real_normed_vector set"
```
```  2556   shows "finite s \<Longrightarrow> bounded (convex hull s)"
```
```  2557   using bounded_convex_hull finite_imp_bounded
```
```  2558   by auto
```
```  2559
```
```  2560
```
```  2561 subsubsection%unimportant \<open>Convex hull is "preserved" by a linear function\<close>
```
```  2562
```
```  2563 lemma convex_hull_linear_image:
```
```  2564   assumes f: "linear f"
```
```  2565   shows "f ` (convex hull s) = convex hull (f ` s)"
```
```  2566 proof
```
```  2567   show "convex hull (f ` s) \<subseteq> f ` (convex hull s)"
```
```  2568     by (intro hull_minimal image_mono hull_subset convex_linear_image assms convex_convex_hull)
```
```  2569   show "f ` (convex hull s) \<subseteq> convex hull (f ` s)"
```
```  2570   proof (unfold image_subset_iff_subset_vimage, rule hull_minimal)
```
```  2571     show "s \<subseteq> f -` (convex hull (f ` s))"
```
```  2572       by (fast intro: hull_inc)
```
```  2573     show "convex (f -` (convex hull (f ` s)))"
```
```  2574       by (intro convex_linear_vimage [OF f] convex_convex_hull)
```
```  2575   qed
```
```  2576 qed
```
```  2577
```
```  2578 lemma in_convex_hull_linear_image:
```
```  2579   assumes "linear f"
```
```  2580     and "x \<in> convex hull s"
```
```  2581   shows "f x \<in> convex hull (f ` s)"
```
```  2582   using convex_hull_linear_image[OF assms(1)] assms(2) by auto
```
```  2583
```
```  2584 lemma convex_hull_Times:
```
```  2585   "convex hull (s \<times> t) = (convex hull s) \<times> (convex hull t)"
```
```  2586 proof
```
```  2587   show "convex hull (s \<times> t) \<subseteq> (convex hull s) \<times> (convex hull t)"
```
```  2588     by (intro hull_minimal Sigma_mono hull_subset convex_Times convex_convex_hull)
```
```  2589   have "\<forall>x\<in>convex hull s. \<forall>y\<in>convex hull t. (x, y) \<in> convex hull (s \<times> t)"
```
```  2590   proof (intro hull_induct)
```
```  2591     fix x y assume "x \<in> s" and "y \<in> t"
```
```  2592     then show "(x, y) \<in> convex hull (s \<times> t)"
```
```  2593       by (simp add: hull_inc)
```
```  2594   next
```
```  2595     fix x let ?S = "((\<lambda>y. (0, y)) -` (\<lambda>p. (- x, 0) + p) ` (convex hull s \<times> t))"
```
```  2596     have "convex ?S"
```
```  2597       by (intro convex_linear_vimage convex_translation convex_convex_hull,
```
```  2598         simp add: linear_iff)
```
```  2599     also have "?S = {y. (x, y) \<in> convex hull (s \<times> t)}"
```
```  2600       by (auto simp add: image_def Bex_def)
```
```  2601     finally show "convex {y. (x, y) \<in> convex hull (s \<times> t)}" .
```
```  2602   next
```
```  2603     show "convex {x. \<forall>y\<in>convex hull t. (x, y) \<in> convex hull (s \<times> t)}"
```
```  2604     proof (unfold Collect_ball_eq, rule convex_INT [rule_format])
```
```  2605       fix y let ?S = "((\<lambda>x. (x, 0)) -` (\<lambda>p. (0, - y) + p) ` (convex hull s \<times> t))"
```
```  2606       have "convex ?S"
```
```  2607       by (intro convex_linear_vimage convex_translation convex_convex_hull,
```
```  2608         simp add: linear_iff)
```
```  2609       also have "?S = {x. (x, y) \<in> convex hull (s \<times> t)}"
```
```  2610         by (auto simp add: image_def Bex_def)
```
```  2611       finally show "convex {x. (x, y) \<in> convex hull (s \<times> t)}" .
```
```  2612     qed
```
```  2613   qed
```
```  2614   then show "(convex hull s) \<times> (convex hull t) \<subseteq> convex hull (s \<times> t)"
```
```  2615     unfolding subset_eq split_paired_Ball_Sigma .
```
```  2616 qed
```
```  2617
```
```  2618
```
```  2619 subsubsection%unimportant \<open>Stepping theorems for convex hulls of finite sets\<close>
```
```  2620
```
```  2621 lemma convex_hull_empty[simp]: "convex hull {} = {}"
```
```  2622   by (rule hull_unique) auto
```
```  2623
```
```  2624 lemma convex_hull_singleton[simp]: "convex hull {a} = {a}"
```
```  2625   by (rule hull_unique) auto
```
```  2626
```
```  2627 lemma convex_hull_insert:
```
```  2628   fixes s :: "'a::real_vector set"
```
```  2629   assumes "s \<noteq> {}"
```
```  2630   shows "convex hull (insert a s) =
```
```  2631     {x. \<exists>u\<ge>0. \<exists>v\<ge>0. \<exists>b. (u + v = 1) \<and> b \<in> (convex hull s) \<and> (x = u *\<^sub>R a + v *\<^sub>R b)}"
```
```  2632   (is "_ = ?hull")
```
```  2633   apply (rule, rule hull_minimal, rule)
```
```  2634   unfolding insert_iff
```
```  2635   prefer 3
```
```  2636   apply rule
```
```  2637 proof -
```
```  2638   fix x
```
```  2639   assume x: "x = a \<or> x \<in> s"
```
```  2640   then show "x \<in> ?hull"
```
```  2641     apply rule
```
```  2642     unfolding mem_Collect_eq
```
```  2643     apply (rule_tac x=1 in exI)
```
```  2644     defer
```
```  2645     apply (rule_tac x=0 in exI)
```
```  2646     using assms hull_subset[of s convex]
```
```  2647     apply auto
```
```  2648     done
```
```  2649 next
```
```  2650   fix x
```
```  2651   assume "x \<in> ?hull"
```
```  2652   then obtain u v b where obt: "u\<ge>0" "v\<ge>0" "u + v = 1" "b \<in> convex hull s" "x = u *\<^sub>R a + v *\<^sub>R b"
```
```  2653     by auto
```
```  2654   have "a \<in> convex hull insert a s" "b \<in> convex hull insert a s"
```
```  2655     using hull_mono[of s "insert a s" convex] hull_mono[of "{a}" "insert a s" convex] and obt(4)
```
```  2656     by auto
```
```  2657   then show "x \<in> convex hull insert a s"
```
```  2658     unfolding obt(5) using obt(1-3)
```
```  2659     by (rule convexD [OF convex_convex_hull])
```
```  2660 next
```
```  2661   show "convex ?hull"
```
```  2662   proof (rule convexI)
```
```  2663     fix x y u v
```
```  2664     assume as: "(0::real) \<le> u" "0 \<le> v" "u + v = 1" "x\<in>?hull" "y\<in>?hull"
```
```  2665     from as(4) obtain u1 v1 b1 where
```
```  2666       obt1: "u1\<ge>0" "v1\<ge>0" "u1 + v1 = 1" "b1 \<in> convex hull s" "x = u1 *\<^sub>R a + v1 *\<^sub>R b1"
```
```  2667       by auto
```
```  2668     from as(5) obtain u2 v2 b2 where
```
```  2669       obt2: "u2\<ge>0" "v2\<ge>0" "u2 + v2 = 1" "b2 \<in> convex hull s" "y = u2 *\<^sub>R a + v2 *\<^sub>R b2"
```
```  2670       by auto
```
```  2671     have *: "\<And>(x::'a) s1 s2. x - s1 *\<^sub>R x - s2 *\<^sub>R x = ((1::real) - (s1 + s2)) *\<^sub>R x"
```
```  2672       by (auto simp add: algebra_simps)
```
```  2673     have **: "\<exists>b \<in> convex hull s. u *\<^sub>R x + v *\<^sub>R y =
```
```  2674       (u * u1) *\<^sub>R a + (v * u2) *\<^sub>R a + (b - (u * u1) *\<^sub>R b - (v * u2) *\<^sub>R b)"
```
```  2675     proof (cases "u * v1 + v * v2 = 0")
```
```  2676       case True
```
```  2677       have *: "\<And>(x::'a) s1 s2. x - s1 *\<^sub>R x - s2 *\<^sub>R x = ((1::real) - (s1 + s2)) *\<^sub>R x"
```
```  2678         by (auto simp add: algebra_simps)
```
```  2679       from True have ***: "u * v1 = 0" "v * v2 = 0"
```
```  2680         using mult_nonneg_nonneg[OF \<open>u\<ge>0\<close> \<open>v1\<ge>0\<close>] mult_nonneg_nonneg[OF \<open>v\<ge>0\<close> \<open>v2\<ge>0\<close>]
```
```  2681         by arith+
```
```  2682       then have "u * u1 + v * u2 = 1"
```
```  2683         using as(3) obt1(3) obt2(3) by auto
```
```  2684       then show ?thesis
```
```  2685         unfolding obt1(5) obt2(5) *
```
```  2686         using assms hull_subset[of s convex]
```
```  2687         by (auto simp add: *** scaleR_right_distrib)
```
```  2688     next
```
```  2689       case False
```
```  2690       have "1 - (u * u1 + v * u2) = (u + v) - (u * u1 + v * u2)"
```
```  2691         using as(3) obt1(3) obt2(3) by (auto simp add: field_simps)
```
```  2692       also have "\<dots> = u * (v1 + u1 - u1) + v * (v2 + u2 - u2)"
```
```  2693         using as(3) obt1(3) obt2(3) by (auto simp add: field_simps)
```
```  2694       also have "\<dots> = u * v1 + v * v2"
```
```  2695         by simp
```
```  2696       finally have **:"1 - (u * u1 + v * u2) = u * v1 + v * v2" by auto
```
```  2697       have "0 \<le> u * v1 + v * v2" "0 \<le> u * v1" "0 \<le> u * v1 + v * v2" "0 \<le> v * v2"
```
```  2698         using as(1,2) obt1(1,2) obt2(1,2) by auto
```
```  2699       then show ?thesis
```
```  2700         unfolding obt1(5) obt2(5)
```
```  2701         unfolding * and **
```
```  2702         using False
```
```  2703         apply (rule_tac
```
```  2704           x = "((u * v1) / (u * v1 + v * v2)) *\<^sub>R b1 + ((v * v2) / (u * v1 + v * v2)) *\<^sub>R b2" in bexI)
```
```  2705         defer
```
```  2706         apply (rule convexD [OF convex_convex_hull])
```
```  2707         using obt1(4) obt2(4)
```
```  2708         unfolding add_divide_distrib[symmetric] and zero_le_divide_iff
```
```  2709         apply (auto simp add: scaleR_left_distrib scaleR_right_distrib)
```
```  2710         done
```
```  2711     qed
```
```  2712     have u1: "u1 \<le> 1"
```
```  2713       unfolding obt1(3)[symmetric] and not_le using obt1(2) by auto
```
```  2714     have u2: "u2 \<le> 1"
```
```  2715       unfolding obt2(3)[symmetric] and not_le using obt2(2) by auto
```
```  2716     have "u1 * u + u2 * v \<le> max u1 u2 * u + max u1 u2 * v"
```
```  2717       apply (rule add_mono)
```
```  2718       apply (rule_tac [!] mult_right_mono)
```
```  2719       using as(1,2) obt1(1,2) obt2(1,2)
```
```  2720       apply auto
```
```  2721       done
```
```  2722     also have "\<dots> \<le> 1"
```
```  2723       unfolding distrib_left[symmetric] and as(3) using u1 u2 by auto
```
```  2724     finally show "u *\<^sub>R x + v *\<^sub>R y \<in> ?hull"
```
```  2725       unfolding mem_Collect_eq
```
```  2726       apply (rule_tac x="u * u1 + v * u2" in exI)
```
```  2727       apply (rule conjI)
```
```  2728       defer
```
```  2729       apply (rule_tac x="1 - u * u1 - v * u2" in exI)
```
```  2730       unfolding Bex_def
```
```  2731       using as(1,2) obt1(1,2) obt2(1,2) **
```
```  2732       apply (auto simp add: algebra_simps)
```
```  2733       done
```
```  2734   qed
```
```  2735 qed
```
```  2736
```
```  2737 lemma convex_hull_insert_alt:
```
```  2738    "convex hull (insert a S) =
```
```  2739       (if S = {} then {a}
```
```  2740       else {(1 - u) *\<^sub>R a + u *\<^sub>R x |x u. 0 \<le> u \<and> u \<le> 1 \<and> x \<in> convex hull S})"
```
```  2741   apply (auto simp: convex_hull_insert)
```
```  2742   using diff_eq_eq apply fastforce
```
```  2743   by (metis add.group_left_neutral add_le_imp_le_diff diff_add_cancel)
```
```  2744
```
```  2745 subsubsection%unimportant \<open>Explicit expression for convex hull\<close>
```
```  2746
```
```  2747 lemma%important convex_hull_indexed:
```
```  2748   fixes s :: "'a::real_vector set"
```
```  2749   shows "convex hull s =
```
```  2750     {y. \<exists>k u x.
```
```  2751       (\<forall>i\<in>{1::nat .. k}. 0 \<le> u i \<and> x i \<in> s) \<and>
```
```  2752       (sum u {1..k} = 1) \<and> (sum (\<lambda>i. u i *\<^sub>R x i) {1..k} = y)}"
```
```  2753   (is "?xyz = ?hull")
```
```  2754   apply%unimportant (rule hull_unique)
```
```  2755   apply rule
```
```  2756   defer
```
```  2757   apply (rule convexI)
```
```  2758 proof -
```
```  2759   fix x
```
```  2760   assume "x\<in>s"
```
```  2761   then show "x \<in> ?hull"
```
```  2762     unfolding mem_Collect_eq
```
```  2763     apply (rule_tac x=1 in exI, rule_tac x="\<lambda>x. 1" in exI)
```
```  2764     apply auto
```
```  2765     done
```
```  2766 next
```
```  2767   fix t
```
```  2768   assume as: "s \<subseteq> t" "convex t"
```
```  2769   show "?hull \<subseteq> t"
```
```  2770     apply rule
```
```  2771     unfolding mem_Collect_eq
```
```  2772     apply (elim exE conjE)
```
```  2773   proof -
```
```  2774     fix x k u y
```
```  2775     assume assm:
```
```  2776       "\<forall>i\<in>{1::nat..k}. 0 \<le> u i \<and> y i \<in> s"
```
```  2777       "sum u {1..k} = 1" "(\<Sum>i = 1..k. u i *\<^sub>R y i) = x"
```
```  2778     show "x\<in>t"
```
```  2779       unfolding assm(3) [symmetric]
```
```  2780       apply (rule as(2)[unfolded convex, rule_format])
```
```  2781       using assm(1,2) as(1) apply auto
```
```  2782       done
```
```  2783   qed
```
```  2784 next
```
```  2785   fix x y u v
```
```  2786   assume uv: "0 \<le> u" "0 \<le> v" "u + v = (1::real)"
```
```  2787   assume xy: "x \<in> ?hull" "y \<in> ?hull"
```
```  2788   from xy obtain k1 u1 x1 where
```
```  2789     x: "\<forall>i\<in>{1::nat..k1}. 0\<le>u1 i \<and> x1 i \<in> s" "sum u1 {Suc 0..k1} = 1" "(\<Sum>i = Suc 0..k1. u1 i *\<^sub>R x1 i) = x"
```
```  2790     by auto
```
```  2791   from xy obtain k2 u2 x2 where
```
```  2792     y: "\<forall>i\<in>{1::nat..k2}. 0\<le>u2 i \<and> x2 i \<in> s" "sum u2 {Suc 0..k2} = 1" "(\<Sum>i = Suc 0..k2. u2 i *\<^sub>R x2 i) = y"
```
```  2793     by auto
```
```  2794   have *: "\<And>P (x1::'a) x2 s1 s2 i.
```
```  2795     (if P i then s1 else s2) *\<^sub>R (if P i then x1 else x2) = (if P i then s1 *\<^sub>R x1 else s2 *\<^sub>R x2)"
```
```  2796     "{1..k1 + k2} \<inter> {1..k1} = {1..k1}" "{1..k1 + k2} \<inter> - {1..k1} = (\<lambda>i. i + k1) ` {1..k2}"
```
```  2797     prefer 3
```
```  2798     apply (rule, rule)
```
```  2799     unfolding image_iff
```
```  2800     apply (rule_tac x = "x - k1" in bexI)
```
```  2801     apply (auto simp add: not_le)
```
```  2802     done
```
```  2803   have inj: "inj_on (\<lambda>i. i + k1) {1..k2}"
```
```  2804     unfolding inj_on_def by auto
```
```  2805   show "u *\<^sub>R x + v *\<^sub>R y \<in> ?hull"
```
```  2806     apply rule
```
```  2807     apply (rule_tac x="k1 + k2" in exI)
```
```  2808     apply (rule_tac x="\<lambda>i. if i \<in> {1..k1} then u * u1 i else v * u2 (i - k1)" in exI)
```
```  2809     apply (rule_tac x="\<lambda>i. if i \<in> {1..k1} then x1 i else x2 (i - k1)" in exI)
```
```  2810     apply (rule, rule)
```
```  2811     defer
```
```  2812     apply rule
```
```  2813     unfolding * and sum.If_cases[OF finite_atLeastAtMost[of 1 "k1 + k2"]] and
```
```  2814       sum.reindex[OF inj] and o_def Collect_mem_eq
```
```  2815     unfolding scaleR_scaleR[symmetric] scaleR_right.sum [symmetric] sum_distrib_left[symmetric]
```
```  2816   proof -
```
```  2817     fix i
```
```  2818     assume i: "i \<in> {1..k1+k2}"
```
```  2819     show "0 \<le> (if i \<in> {1..k1} then u * u1 i else v * u2 (i - k1)) \<and>
```
```  2820       (if i \<in> {1..k1} then x1 i else x2 (i - k1)) \<in> s"
```
```  2821     proof (cases "i\<in>{1..k1}")
```
```  2822       case True
```
```  2823       then show ?thesis
```
```  2824         using uv(1) x(1)[THEN bspec[where x=i]] by auto
```
```  2825     next
```
```  2826       case False
```
```  2827       define j where "j = i - k1"
```
```  2828       from i False have "j \<in> {1..k2}"
```
```  2829         unfolding j_def by auto
```
```  2830       then show ?thesis
```
```  2831         using False uv(2) y(1)[THEN bspec[where x=j]]
```
```  2832         by (auto simp: j_def[symmetric])
```
```  2833     qed
```
```  2834   qed (auto simp add: not_le x(2,3) y(2,3) uv(3))
```
```  2835 qed
```
```  2836
```
```  2837 lemma convex_hull_finite:
```
```  2838   fixes s :: "'a::real_vector set"
```
```  2839   assumes "finite s"
```
```  2840   shows "convex hull s = {y. \<exists>u. (\<forall>x\<in>s. 0 \<le> u x) \<and>
```
```  2841     sum u s = 1 \<and> sum (\<lambda>x. u x *\<^sub>R x) s = y}"
```
```  2842   (is "?HULL = ?set")
```
```  2843 proof (rule hull_unique, auto simp add: convex_def[of ?set])
```
```  2844   fix x
```
```  2845   assume "x \<in> s"
```
```  2846   then show "\<exists>u. (\<forall>x\<in>s. 0 \<le> u x) \<and> sum u s = 1 \<and> (\<Sum>x\<in>s. u x *\<^sub>R x) = x"
```
```  2847     apply (rule_tac x="\<lambda>y. if x=y then 1 else 0" in exI)
```
```  2848     apply auto
```
```  2849     unfolding sum.delta'[OF assms] and sum_delta''[OF assms]
```
```  2850     apply auto
```
```  2851     done
```
```  2852 next
```
```  2853   fix u v :: real
```
```  2854   assume uv: "0 \<le> u" "0 \<le> v" "u + v = 1"
```
```  2855   fix ux assume ux: "\<forall>x\<in>s. 0 \<le> ux x" "sum ux s = (1::real)"
```
```  2856   fix uy assume uy: "\<forall>x\<in>s. 0 \<le> uy x" "sum uy s = (1::real)"
```
```  2857   {
```
```  2858     fix x
```
```  2859     assume "x\<in>s"
```
```  2860     then have "0 \<le> u * ux x + v * uy x"
```
```  2861       using ux(1)[THEN bspec[where x=x]] uy(1)[THEN bspec[where x=x]] and uv(1,2)
```
```  2862       by auto
```
```  2863   }
```
```  2864   moreover
```
```  2865   have "(\<Sum>x\<in>s. u * ux x + v * uy x) = 1"
```
```  2866     unfolding sum.distrib and sum_distrib_left[symmetric] and ux(2) uy(2)
```
```  2867     using uv(3) by auto
```
```  2868   moreover
```
```  2869   have "(\<Sum>x\<in>s. (u * ux x + v * uy x) *\<^sub>R x) = u *\<^sub>R (\<Sum>x\<in>s. ux x *\<^sub>R x) + v *\<^sub>R (\<Sum>x\<in>s. uy x *\<^sub>R x)"
```
```  2870     unfolding scaleR_left_distrib and sum.distrib and scaleR_scaleR[symmetric]
```
```  2871       and scaleR_right.sum [symmetric]
```
```  2872     by auto
```
```  2873   ultimately
```
```  2874   show "\<exists>uc. (\<forall>x\<in>s. 0 \<le> uc x) \<and> sum uc s = 1 \<and>
```
```  2875       (\<Sum>x\<in>s. uc x *\<^sub>R x) = u *\<^sub>R (\<Sum>x\<in>s. ux x *\<^sub>R x) + v *\<^sub>R (\<Sum>x\<in>s. uy x *\<^sub>R x)"
```
```  2876     apply (rule_tac x="\<lambda>x. u * ux x + v * uy x" in exI)
```
```  2877     apply auto
```
```  2878     done
```
```  2879 next
```
```  2880   fix t
```
```  2881   assume t: "s \<subseteq> t" "convex t"
```
```  2882   fix u
```
```  2883   assume u: "\<forall>x\<in>s. 0 \<le> u x" "sum u s = (1::real)"
```
```  2884   then show "(\<Sum>x\<in>s. u x *\<^sub>R x) \<in> t"
```
```  2885     using t(2)[unfolded convex_explicit, THEN spec[where x=s], THEN spec[where x=u]]
```
```  2886     using assms and t(1) by auto
```
```  2887 qed
```
```  2888
```
```  2889
```
```  2890 subsubsection%unimportant \<open>Another formulation from Lars Schewe\<close>
```
```  2891
```
```  2892 lemma convex_hull_explicit:
```
```  2893   fixes p :: "'a::real_vector set"
```
```  2894   shows "convex hull p =
```
```  2895     {y. \<exists>s u. finite s \<and> s \<subseteq> p \<and> (\<forall>x\<in>s. 0 \<le> u x) \<and> sum u s = 1 \<and> sum (\<lambda>v. u v *\<^sub>R v) s = y}"
```
```  2896   (is "?lhs = ?rhs")
```
```  2897 proof -
```
```  2898   {
```
```  2899     fix x
```
```  2900     assume "x\<in>?lhs"
```
```  2901     then obtain k u y where
```
```  2902         obt: "\<forall>i\<in>{1::nat..k}. 0 \<le> u i \<and> y i \<in> p" "sum u {1..k} = 1" "(\<Sum>i = 1..k. u i *\<^sub>R y i) = x"
```
```  2903       unfolding convex_hull_indexed by auto
```
```  2904
```
```  2905     have fin: "finite {1..k}" by auto
```
```  2906     have fin': "\<And>v. finite {i \<in> {1..k}. y i = v}" by auto
```
```  2907     {
```
```  2908       fix j
```
```  2909       assume "j\<in>{1..k}"
```
```  2910       then have "y j \<in> p" "0 \<le> sum u {i. Suc 0 \<le> i \<and> i \<le> k \<and> y i = y j}"
```
```  2911         using obt(1)[THEN bspec[where x=j]] and obt(2)
```
```  2912         apply simp
```
```  2913         apply (rule sum_nonneg)
```
```  2914         using obt(1)
```
```  2915         apply auto
```
```  2916         done
```
```  2917     }
```
```  2918     moreover
```
```  2919     have "(\<Sum>v\<in>y ` {1..k}. sum u {i \<in> {1..k}. y i = v}) = 1"
```
```  2920       unfolding sum_image_gen[OF fin, symmetric] using obt(2) by auto
```
```  2921     moreover have "(\<Sum>v\<in>y ` {1..k}. sum u {i \<in> {1..k}. y i = v} *\<^sub>R v) = x"
```
```  2922       using sum_image_gen[OF fin, of "\<lambda>i. u i *\<^sub>R y i" y, symmetric]
```
```  2923       unfolding scaleR_left.sum using obt(3) by auto
```
```  2924     ultimately
```
```  2925     have "\<exists>s u. finite s \<and> s \<subseteq> p \<and> (\<forall>x\<in>s. 0 \<le> u x) \<and> sum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = x"
```
```  2926       apply (rule_tac x="y ` {1..k}" in exI)
```
```  2927       apply (rule_tac x="\<lambda>v. sum u {i\<in>{1..k}. y i = v}" in exI)
```
```  2928       apply auto
```
```  2929       done
```
```  2930     then have "x\<in>?rhs" by auto
```
```  2931   }
```
```  2932   moreover
```
```  2933   {
```
```  2934     fix y
```
```  2935     assume "y\<in>?rhs"
```
```  2936     then obtain s u where
```
```  2937       obt: "finite s" "s \<subseteq> p" "\<forall>x\<in>s. 0 \<le> u x" "sum u s = 1" "(\<Sum>v\<in>s. u v *\<^sub>R v) = y"
```
```  2938       by auto
```
```  2939
```
```  2940     obtain f where f: "inj_on f {1..card s}" "f ` {1..card s} = s"
```
```  2941       using ex_bij_betw_nat_finite_1[OF obt(1)] unfolding bij_betw_def by auto
```
```  2942
```
```  2943     {
```
```  2944       fix i :: nat
```
```  2945       assume "i\<in>{1..card s}"
```
```  2946       then have "f i \<in> s"
```
```  2947         apply (subst f(2)[symmetric])
```
```  2948         apply auto
```
```  2949         done
```
```  2950       then have "0 \<le> u (f i)" "f i \<in> p" using obt(2,3) by auto
```
```  2951     }
```
```  2952     moreover have *: "finite {1..card s}" by auto
```
```  2953     {
```
```  2954       fix y
```
```  2955       assume "y\<in>s"
```
```  2956       then obtain i where "i\<in>{1..card s}" "f i = y"
```
```  2957         using f using image_iff[of y f "{1..card s}"]
```
```  2958         by auto
```
```  2959       then have "{x. Suc 0 \<le> x \<and> x \<le> card s \<and> f x = y} = {i}"
```
```  2960         apply auto
```
```  2961         using f(1)[unfolded inj_on_def]
```
```  2962         apply(erule_tac x=x in ballE)
```
```  2963         apply auto
```
```  2964         done
```
```  2965       then have "card {x. Suc 0 \<le> x \<and> x \<le> card s \<and> f x = y} = 1" by auto
```
```  2966       then have "(\<Sum>x\<in>{x \<in> {1..card s}. f x = y}. u (f x)) = u y"
```
```  2967           "(\<Sum>x\<in>{x \<in> {1..card s}. f x = y}. u (f x) *\<^sub>R f x) = u y *\<^sub>R y"
```
```  2968         by (auto simp add: sum_constant_scaleR)
```
```  2969     }
```
```  2970     then have "(\<Sum>x = 1..card s. u (f x)) = 1" "(\<Sum>i = 1..card s. u (f i) *\<^sub>R f i) = y"
```
```  2971       unfolding sum_image_gen[OF *(1), of "\<lambda>x. u (f x) *\<^sub>R f x" f]
```
```  2972         and sum_image_gen[OF *(1), of "\<lambda>x. u (f x)" f]
```
```  2973       unfolding f
```
```  2974       using sum.cong [of s s "\<lambda>y. (\<Sum>x\<in>{x \<in> {1..card s}. f x = y}. u (f x) *\<^sub>R f x)" "\<lambda>v. u v *\<^sub>R v"]
```
```  2975       using sum.cong [of s s "\<lambda>y. (\<Sum>x\<in>{x \<in> {1..card s}. f x = y}. u (f x))" u]
```
```  2976       unfolding obt(4,5)
```
```  2977       by auto
```
```  2978     ultimately
```
```  2979     have "\<exists>k u x. (\<forall>i\<in>{1..k}. 0 \<le> u i \<and> x i \<in> p) \<and> sum u {1..k} = 1 \<and>
```
```  2980         (\<Sum>i::nat = 1..k. u i *\<^sub>R x i) = y"
```
```  2981       apply (rule_tac x="card s" in exI)
```
```  2982       apply (rule_tac x="u \<circ> f" in exI)
```
```  2983       apply (rule_tac x=f in exI)
```
```  2984       apply fastforce
```
```  2985       done
```
```  2986     then have "y \<in> ?lhs"
```
```  2987       unfolding convex_hull_indexed by auto
```
```  2988   }
```
```  2989   ultimately show ?thesis
```
```  2990     unfolding set_eq_iff by blast
```
```  2991 qed
```
```  2992
```
```  2993
```
```  2994 subsubsection%unimportant \<open>A stepping theorem for that expansion\<close>
```
```  2995
```
```  2996 lemma convex_hull_finite_step:
```
```  2997   fixes s :: "'a::real_vector set"
```
```  2998   assumes "finite s"
```
```  2999   shows
```
```  3000     "(\<exists>u. (\<forall>x\<in>insert a s. 0 \<le> u x) \<and> sum u (insert a s) = w \<and> sum (\<lambda>x. u x *\<^sub>R x) (insert a s) = y)
```
```  3001       \<longleftrightarrow> (\<exists>v\<ge>0. \<exists>u. (\<forall>x\<in>s. 0 \<le> u x) \<and> sum u s = w - v \<and> sum (\<lambda>x. u x *\<^sub>R x) s = y - v *\<^sub>R a)"
```
```  3002   (is "?lhs = ?rhs")
```
```  3003 proof (rule, case_tac[!] "a\<in>s")
```
```  3004   assume "a \<in> s"
```
```  3005   then have *: "insert a s = s" by auto
```
```  3006   assume ?lhs
```
```  3007   then show ?rhs
```
```  3008     unfolding *
```
```  3009     apply (rule_tac x=0 in exI)
```
```  3010     apply auto
```
```  3011     done
```
```  3012 next
```
```  3013   assume ?lhs
```
```  3014   then obtain u where
```
```  3015       u: "\<forall>x\<in>insert a s. 0 \<le> u x" "sum u (insert a s) = w" "(\<Sum>x\<in>insert a s. u x *\<^sub>R x) = y"
```
```  3016     by auto
```
```  3017   assume "a \<notin> s"
```
```  3018   then show ?rhs
```
```  3019     apply (rule_tac x="u a" in exI)
```
```  3020     using u(1)[THEN bspec[where x=a]]
```
```  3021     apply simp
```
```  3022     apply (rule_tac x=u in exI)
```
```  3023     using u[unfolded sum_clauses(2)[OF assms]] and \<open>a\<notin>s\<close>
```
```  3024     apply auto
```
```  3025     done
```
```  3026 next
```
```  3027   assume "a \<in> s"
```
```  3028   then have *: "insert a s = s" by auto
```
```  3029   have fin: "finite (insert a s)" using assms by auto
```
```  3030   assume ?rhs
```
```  3031   then obtain v u where uv: "v\<ge>0" "\<forall>x\<in>s. 0 \<le> u x" "sum u s = w - v" "(\<Sum>x\<in>s. u x *\<^sub>R x) = y - v *\<^sub>R a"
```
```  3032     by auto
```
```  3033   show ?lhs
```
```  3034     apply (rule_tac x = "\<lambda>x. (if a = x then v else 0) + u x" in exI)
```
```  3035     unfolding scaleR_left_distrib and sum.distrib and sum_delta''[OF fin] and sum.delta'[OF fin]
```
```  3036     unfolding sum_clauses(2)[OF assms]
```
```  3037     using uv and uv(2)[THEN bspec[where x=a]] and \<open>a\<in>s\<close>
```
```  3038     apply auto
```
```  3039     done
```
```  3040 next
```
```  3041   assume ?rhs
```
```  3042   then obtain v u where
```
```  3043     uv: "v\<ge>0" "\<forall>x\<in>s. 0 \<le> u x" "sum u s = w - v" "(\<Sum>x\<in>s. u x *\<^sub>R x) = y - v *\<^sub>R a"
```
```  3044     by auto
```
```  3045   moreover
```
```  3046   assume "a \<notin> s"
```
```  3047   moreover
```
```  3048   have "(\<Sum>x\<in>s. if a = x then v else u x) = sum u s"
```
```  3049     and "(\<Sum>x\<in>s. (if a = x then v else u x) *\<^sub>R x) = (\<Sum>x\<in>s. u x *\<^sub>R x)"
```
```  3050     apply (rule_tac sum.cong) apply rule
```
```  3051     defer
```
```  3052     apply (rule_tac sum.cong) apply rule
```
```  3053     using \<open>a \<notin> s\<close>
```
```  3054     apply auto
```
```  3055     done
```
```  3056   ultimately show ?lhs
```
```  3057     apply (rule_tac x="\<lambda>x. if a = x then v else u x" in exI)
```
```  3058     unfolding sum_clauses(2)[OF assms]
```
```  3059     apply auto
```
```  3060     done
```
```  3061 qed
```
```  3062
```
```  3063
```
```  3064 subsubsection%unimportant \<open>Hence some special cases\<close>
```
```  3065
```
```  3066 lemma convex_hull_2:
```
```  3067   "convex hull {a,b} = {u *\<^sub>R a + v *\<^sub>R b | u v. 0 \<le> u \<and> 0 \<le> v \<and> u + v = 1}"
```
```  3068 proof -
```
```  3069   have *: "\<And>u. (\<forall>x\<in>{a, b}. 0 \<le> u x) \<longleftrightarrow> 0 \<le> u a \<and> 0 \<le> u b"
```
```  3070     by auto
```
```  3071   have **: "finite {b}" by auto
```
```  3072   show ?thesis
```
```  3073     apply (simp add: convex_hull_finite)
```
```  3074     unfolding convex_hull_finite_step[OF **, of a 1, unfolded * conj_assoc]
```
```  3075     apply auto
```
```  3076     apply (rule_tac x=v in exI)
```
```  3077     apply (rule_tac x="1 - v" in exI)
```
```  3078     apply simp
```
```  3079     apply (rule_tac x=u in exI)
```
```  3080     apply simp
```
```  3081     apply (rule_tac x="\<lambda>x. v" in exI)
```
```  3082     apply simp
```
```  3083     done
```
```  3084 qed
```
```  3085
```
```  3086 lemma convex_hull_2_alt: "convex hull {a,b} = {a + u *\<^sub>R (b - a) | u.  0 \<le> u \<and> u \<le> 1}"
```
```  3087   unfolding convex_hull_2
```
```  3088 proof (rule Collect_cong)
```
```  3089   have *: "\<And>x y ::real. x + y = 1 \<longleftrightarrow> x = 1 - y"
```
```  3090     by auto
```
```  3091   fix x
```
```  3092   show "(\<exists>v u. x = v *\<^sub>R a + u *\<^sub>R b \<and> 0 \<le> v \<and> 0 \<le> u \<and> v + u = 1) \<longleftrightarrow>
```
```  3093     (\<exists>u. x = a + u *\<^sub>R (b - a) \<and> 0 \<le> u \<and> u \<le> 1)"
```
```  3094     unfolding *
```
```  3095     apply auto
```
```  3096     apply (rule_tac[!] x=u in exI)
```
```  3097     apply (auto simp add: algebra_simps)
```
```  3098     done
```
```  3099 qed
```
```  3100
```
```  3101 lemma convex_hull_3:
```
```  3102   "convex hull {a,b,c} = { u *\<^sub>R a + v *\<^sub>R b + w *\<^sub>R c | u v w. 0 \<le> u \<and> 0 \<le> v \<and> 0 \<le> w \<and> u + v + w = 1}"
```
```  3103 proof -
```
```  3104   have fin: "finite {a,b,c}" "finite {b,c}" "finite {c}"
```
```  3105     by auto
```
```  3106   have *: "\<And>x y z ::real. x + y + z = 1 \<longleftrightarrow> x = 1 - y - z"
```
```  3107     by (auto simp add: field_simps)
```
```  3108   show ?thesis
```
```  3109     unfolding convex_hull_finite[OF fin(1)] and convex_hull_finite_step[OF fin(2)] and *
```
```  3110     unfolding convex_hull_finite_step[OF fin(3)]
```
```  3111     apply (rule Collect_cong)
```
```  3112     apply simp
```
```  3113     apply auto
```
```  3114     apply (rule_tac x=va in exI)
```
```  3115     apply (rule_tac x="u c" in exI)
```
```  3116     apply simp
```
```  3117     apply (rule_tac x="1 - v - w" in exI)
```
```  3118     apply simp
```
```  3119     apply (rule_tac x=v in exI)
```
```  3120     apply simp
```
```  3121     apply (rule_tac x="\<lambda>x. w" in exI)
```
```  3122     apply simp
```
```  3123     done
```
```  3124 qed
```
```  3125
```
```  3126 lemma convex_hull_3_alt:
```
```  3127   "convex hull {a,b,c} = {a + u *\<^sub>R (b - a) + v *\<^sub>R (c - a) | u v.  0 \<le> u \<and> 0 \<le> v \<and> u + v \<le> 1}"
```
```  3128 proof -
```
```  3129   have *: "\<And>x y z ::real. x + y + z = 1 \<longleftrightarrow> x = 1 - y - z"
```
```  3130     by auto
```
```  3131   show ?thesis
```
```  3132     unfolding convex_hull_3
```
```  3133     apply (auto simp add: *)
```
```  3134     apply (rule_tac x=v in exI)
```
```  3135     apply (rule_tac x=w in exI)
```
```  3136     apply (simp add: algebra_simps)
```
```  3137     apply (rule_tac x=u in exI)
```
```  3138     apply (rule_tac x=v in exI)
```
```  3139     apply (simp add: algebra_simps)
```
```  3140     done
```
```  3141 qed
```
```  3142
```
```  3143
```
```  3144 subsection%unimportant \<open>Relations among closure notions and corresponding hulls\<close>
```
```  3145
```
```  3146 lemma affine_imp_convex: "affine s \<Longrightarrow> convex s"
```
```  3147   unfolding affine_def convex_def by auto
```
```  3148
```
```  3149 lemma convex_affine_hull [simp]: "convex (affine hull S)"
```
```  3150   by (simp add: affine_imp_convex)
```
```  3151
```
```  3152 lemma subspace_imp_convex: "subspace s \<Longrightarrow> convex s"
```
```  3153   using subspace_imp_affine affine_imp_convex by auto
```
```  3154
```
```  3155 lemma affine_hull_subset_span: "(affine hull s) \<subseteq> (span s)"
```
```  3156   by (metis hull_minimal span_inc subspace_imp_affine subspace_span)
```
```  3157
```
```  3158 lemma convex_hull_subset_span: "(convex hull s) \<subseteq> (span s)"
```
```  3159   by (metis hull_minimal span_inc subspace_imp_convex subspace_span)
```
```  3160
```
```  3161 lemma convex_hull_subset_affine_hull: "(convex hull s) \<subseteq> (affine hull s)"
```
```  3162   by (metis affine_affine_hull affine_imp_convex hull_minimal hull_subset)
```
```  3163
```
```  3164 lemma affine_dependent_imp_dependent: "affine_dependent s \<Longrightarrow> dependent s"
```
```  3165   unfolding affine_dependent_def dependent_def
```
```  3166   using affine_hull_subset_span by auto
```
```  3167
```
```  3168 lemma dependent_imp_affine_dependent:
```
```  3169   assumes "dependent {x - a| x . x \<in> s}"
```
```  3170     and "a \<notin> s"
```
```  3171   shows "affine_dependent (insert a s)"
```
```  3172 proof -
```
```  3173   from assms(1)[unfolded dependent_explicit] obtain S u v
```
```  3174     where obt: "finite S" "S \<subseteq> {x - a |x. x \<in> s}" "v\<in>S" "u v  \<noteq> 0" "(\<Sum>v\<in>S. u v *\<^sub>R v) = 0"
```
```  3175     by auto
```
```  3176   define t where "t = (\<lambda>x. x + a) ` S"
```
```  3177
```
```  3178   have inj: "inj_on (\<lambda>x. x + a) S"
```
```  3179     unfolding inj_on_def by auto
```
```  3180   have "0 \<notin> S"
```
```  3181     using obt(2) assms(2) unfolding subset_eq by auto
```
```  3182   have fin: "finite t" and "t \<subseteq> s"
```
```  3183     unfolding t_def using obt(1,2) by auto
```
```  3184   then have "finite (insert a t)" and "insert a t \<subseteq> insert a s"
```
```  3185     by auto
```
```  3186   moreover have *: "\<And>P Q. (\<Sum>x\<in>t. (if x = a then P x else Q x)) = (\<Sum>x\<in>t. Q x)"
```
```  3187     apply (rule sum.cong)
```
```  3188     using \<open>a\<notin>s\<close> \<open>t\<subseteq>s\<close>
```
```  3189     apply auto
```
```  3190     done
```
```  3191   have "(\<Sum>x\<in>insert a t. if x = a then - (\<Sum>x\<in>t. u (x - a)) else u (x - a)) = 0"
```
```  3192     unfolding sum_clauses(2)[OF fin]
```
```  3193     using \<open>a\<notin>s\<close> \<open>t\<subseteq>s\<close>
```
```  3194     apply auto
```
```  3195     unfolding *
```
```  3196     apply auto
```
```  3197     done
```
```  3198   moreover have "\<exists>v\<in>insert a t. (if v = a then - (\<Sum>x\<in>t. u (x - a)) else u (v - a)) \<noteq> 0"
```
```  3199     apply (rule_tac x="v + a" in bexI)
```
```  3200     using obt(3,4) and \<open>0\<notin>S\<close>
```
```  3201     unfolding t_def
```
```  3202     apply auto
```
```  3203     done
```
```  3204   moreover have *: "\<And>P Q. (\<Sum>x\<in>t. (if x = a then P x else Q x) *\<^sub>R x) = (\<Sum>x\<in>t. Q x *\<^sub>R x)"
```
```  3205     apply (rule sum.cong)
```
```  3206     using \<open>a\<notin>s\<close> \<open>t\<subseteq>s\<close>
```
```  3207     apply auto
```
```  3208     done
```
```  3209   have "(\<Sum>x\<in>t. u (x - a)) *\<^sub>R a = (\<Sum>v\<in>t. u (v - a) *\<^sub>R v)"
```
```  3210     unfolding scaleR_left.sum
```
```  3211     unfolding t_def and sum.reindex[OF inj] and o_def
```
```  3212     using obt(5)
```
```  3213     by (auto simp add: sum.distrib scaleR_right_distrib)
```
```  3214   then have "(\<Sum>v\<in>insert a t. (if v = a then - (\<Sum>x\<in>t. u (x - a)) else u (v - a)) *\<^sub>R v) = 0"
```
```  3215     unfolding sum_clauses(2)[OF fin]
```
```  3216     using \<open>a\<notin>s\<close> \<open>t\<subseteq>s\<close>
```
```  3217     by (auto simp add: *)
```
```  3218   ultimately show ?thesis
```
```  3219     unfolding affine_dependent_explicit
```
```  3220     apply (rule_tac x="insert a t" in exI)
```
```  3221     apply auto
```
```  3222     done
```
```  3223 qed
```
```  3224
```
```  3225 lemma convex_cone:
```
```  3226   "convex s \<and> cone s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. (x + y) \<in> s) \<and> (\<forall>x\<in>s. \<forall>c\<ge>0. (c *\<^sub>R x) \<in> s)"
```
```  3227   (is "?lhs = ?rhs")
```
```  3228 proof -
```
```  3229   {
```
```  3230     fix x y
```
```  3231     assume "x\<in>s" "y\<in>s" and ?lhs
```
```  3232     then have "2 *\<^sub>R x \<in>s" "2 *\<^sub>R y \<in> s"
```
```  3233       unfolding cone_def by auto
```
```  3234     then have "x + y \<in> s"
```
```  3235       using \<open>?lhs\<close>[unfolded convex_def, THEN conjunct1]
```
```  3236       apply (erule_tac x="2*\<^sub>R x" in ballE)
```
```  3237       apply (erule_tac x="2*\<^sub>R y" in ballE)
```
```  3238       apply (erule_tac x="1/2" in allE)
```
```  3239       apply simp
```
```  3240       apply (erule_tac x="1/2" in allE)
```
```  3241       apply auto
```
```  3242       done
```
```  3243   }
```
```  3244   then show ?thesis
```
```  3245     unfolding convex_def cone_def by blast
```
```  3246 qed
```
```  3247
```
```  3248 lemma affine_dependent_biggerset:
```
```  3249   fixes s :: "'a::euclidean_space set"
```
```  3250   assumes "finite s" "card s \<ge> DIM('a) + 2"
```
```  3251   shows "affine_dependent s"
```
```  3252 proof -
```
```  3253   have "s \<noteq> {}" using assms by auto
```
```  3254   then obtain a where "a\<in>s" by auto
```
```  3255   have *: "{x - a |x. x \<in> s - {a}} = (\<lambda>x. x - a) ` (s - {a})"
```
```  3256     by auto
```
```  3257   have "card {x - a |x. x \<in> s - {a}} = card (s - {a})"
```
```  3258     unfolding *
```
```  3259     apply (rule card_image)
```
```  3260     unfolding inj_on_def
```
```  3261     apply auto
```
```  3262     done
```
```  3263   also have "\<dots> > DIM('a)" using assms(2)
```
```  3264     unfolding card_Diff_singleton[OF assms(1) \<open>a\<in>s\<close>] by auto
```
```  3265   finally show ?thesis
```
```  3266     apply (subst insert_Diff[OF \<open>a\<in>s\<close>, symmetric])
```
```  3267     apply (rule dependent_imp_affine_dependent)
```
```  3268     apply (rule dependent_biggerset)
```
```  3269     apply auto
```
```  3270     done
```
```  3271 qed
```
```  3272
```
```  3273 lemma affine_dependent_biggerset_general:
```
```  3274   assumes "finite (s :: 'a::euclidean_space set)"
```
```  3275     and "card s \<ge> dim s + 2"
```
```  3276   shows "affine_dependent s"
```
```  3277 proof -
```
```  3278   from assms(2) have "s \<noteq> {}" by auto
```
```  3279   then obtain a where "a\<in>s" by auto
```
```  3280   have *: "{x - a |x. x \<in> s - {a}} = (\<lambda>x. x - a) ` (s - {a})"
```
```  3281     by auto
```
```  3282   have **: "card {x - a |x. x \<in> s - {a}} = card (s - {a})"
```
```  3283     unfolding *
```
```  3284     apply (rule card_image)
```
```  3285     unfolding inj_on_def
```
```  3286     apply auto
```
```  3287     done
```
```  3288   have "dim {x - a |x. x \<in> s - {a}} \<le> dim s"
```
```  3289     apply (rule subset_le_dim)
```
```  3290     unfolding subset_eq
```
```  3291     using \<open>a\<in>s\<close>
```
```  3292     apply (auto simp add:span_superset span_diff)
```
```  3293     done
```
```  3294   also have "\<dots> < dim s + 1" by auto
```
```  3295   also have "\<dots> \<le> card (s - {a})"
```
```  3296     using assms
```
```  3297     using card_Diff_singleton[OF assms(1) \<open>a\<in>s\<close>]
```
```  3298     by auto
```
```  3299   finally show ?thesis
```
```  3300     apply (subst insert_Diff[OF \<open>a\<in>s\<close>, symmetric])
```
```  3301     apply (rule dependent_imp_affine_dependent)
```
```  3302     apply (rule dependent_biggerset_general)
```
```  3303     unfolding **
```
```  3304     apply auto
```
```  3305     done
```
```  3306 qed
```
```  3307
```
```  3308
```
```  3309 subsection%unimportant \<open>Some Properties of Affine Dependent Sets\<close>
```
```  3310
```
```  3311 lemma affine_independent_0 [simp]: "\<not> affine_dependent {}"
```
```  3312   by (simp add: affine_dependent_def)
```
```  3313
```
```  3314 lemma affine_independent_1 [simp]: "\<not> affine_dependent {a}"
```
```  3315   by (simp add: affine_dependent_def)
```
```  3316
```
```  3317 lemma affine_independent_2 [simp]: "\<not> affine_dependent {a,b}"
```
```  3318   by (simp add: affine_dependent_def insert_Diff_if hull_same)
```
```  3319
```
```  3320 lemma affine_hull_translation: "affine hull ((\<lambda>x. a + x) `  S) = (\<lambda>x. a + x) ` (affine hull S)"
```
```  3321 proof -
```
```  3322   have "affine ((\<lambda>x. a + x) ` (affine hull S))"
```
```  3323     using affine_translation affine_affine_hull by blast
```
```  3324   moreover have "(\<lambda>x. a + x) `  S \<subseteq> (\<lambda>x. a + x) ` (affine hull S)"
```
```  3325     using hull_subset[of S] by auto
```
```  3326   ultimately have h1: "affine hull ((\<lambda>x. a + x) `  S) \<subseteq> (\<lambda>x. a + x) ` (affine hull S)"
```
```  3327     by (metis hull_minimal)
```
```  3328   have "affine((\<lambda>x. -a + x) ` (affine hull ((\<lambda>x. a + x) `  S)))"
```
```  3329     using affine_translation affine_affine_hull by blast
```
```  3330   moreover have "(\<lambda>x. -a + x) ` (\<lambda>x. a + x) `  S \<subseteq> (\<lambda>x. -a + x) ` (affine hull ((\<lambda>x. a + x) `  S))"
```
```  3331     using hull_subset[of "(\<lambda>x. a + x) `  S"] by auto
```
```  3332   moreover have "S = (\<lambda>x. -a + x) ` (\<lambda>x. a + x) `  S"
```
```  3333     using translation_assoc[of "-a" a] by auto
```
```  3334   ultimately have "(\<lambda>x. -a + x) ` (affine hull ((\<lambda>x. a + x) `  S)) >= (affine hull S)"
```
```  3335     by (metis hull_minimal)
```
```  3336   then have "affine hull ((\<lambda>x. a + x) ` S) >= (\<lambda>x. a + x) ` (affine hull S)"
```
```  3337     by auto
```
```  3338   then show ?thesis using h1 by auto
```
```  3339 qed
```
```  3340
```
```  3341 lemma affine_dependent_translation:
```
```  3342   assumes "affine_dependent S"
```
```  3343   shows "affine_dependent ((\<lambda>x. a + x) ` S)"
```
```  3344 proof -
```
```  3345   obtain x where x: "x \<in> S \<and> x \<in> affine hull (S - {x})"
```
```  3346     using assms affine_dependent_def by auto
```
```  3347   have "(+) a ` (S - {x}) = (+) a ` S - {a + x}"
```
```  3348     by auto
```
```  3349   then have "a + x \<in> affine hull ((\<lambda>x. a + x) ` S - {a + x})"
```
```  3350     using affine_hull_translation[of a "S - {x}"] x by auto
```
```  3351   moreover have "a + x \<in> (\<lambda>x. a + x) ` S"
```
```  3352     using x by auto
```
```  3353   ultimately show ?thesis
```
```  3354     unfolding affine_dependent_def by auto
```
```  3355 qed
```
```  3356
```
```  3357 lemma affine_dependent_translation_eq:
```
```  3358   "affine_dependent S \<longleftrightarrow> affine_dependent ((\<lambda>x. a + x) ` S)"
```
```  3359 proof -
```
```  3360   {
```
```  3361     assume "affine_dependent ((\<lambda>x. a + x) ` S)"
```
```  3362     then have "affine_dependent S"
```
```  3363       using affine_dependent_translation[of "((\<lambda>x. a + x) ` S)" "-a"] translation_assoc[of "-a" a]
```
```  3364       by auto
```
```  3365   }
```
```  3366   then show ?thesis
```
```  3367     using affine_dependent_translation by auto
```
```  3368 qed
```
```  3369
```
```  3370 lemma affine_hull_0_dependent:
```
```  3371   assumes "0 \<in> affine hull S"
```
```  3372   shows "dependent S"
```
```  3373 proof -
```
```  3374   obtain s u where s_u: "finite s \<and> s \<noteq> {} \<and> s \<subseteq> S \<and> sum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = 0"
```
```  3375     using assms affine_hull_explicit[of S] by auto
```
```  3376   then have "\<exists>v\<in>s. u v \<noteq> 0"
```
```  3377     using sum_not_0[of "u" "s"] by auto
```
```  3378   then have "finite s \<and> s \<subseteq> S \<and> (\<exists>v\<in>s. u v \<noteq> 0 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = 0)"
```
```  3379     using s_u by auto
```
```  3380   then show ?thesis
```
```  3381     unfolding dependent_explicit[of S] by auto
```
```  3382 qed
```
```  3383
```
```  3384 lemma affine_dependent_imp_dependent2:
```
```  3385   assumes "affine_dependent (insert 0 S)"
```
```  3386   shows "dependent S"
```
```  3387 proof -
```
```  3388   obtain x where x: "x \<in> insert 0 S \<and> x \<in> affine hull (insert 0 S - {x})"
```
```  3389     using affine_dependent_def[of "(insert 0 S)"] assms by blast
```
```  3390   then have "x \<in> span (insert 0 S - {x})"
```
```  3391     using affine_hull_subset_span by auto
```
```  3392   moreover have "span (insert 0 S - {x}) = span (S - {x})"
```
```  3393     using insert_Diff_if[of "0" S "{x}"] span_insert_0[of "S-{x}"] by auto
```
```  3394   ultimately have "x \<in> span (S - {x})" by auto
```
```  3395   then have "x \<noteq> 0 \<Longrightarrow> dependent S"
```
```  3396     using x dependent_def by auto
```
```  3397   moreover
```
```  3398   {
```
```  3399     assume "x = 0"
```
```  3400     then have "0 \<in> affine hull S"
```
```  3401       using x hull_mono[of "S - {0}" S] by auto
```
```  3402     then have "dependent S"
```
```  3403       using affine_hull_0_dependent by auto
```
```  3404   }
```
```  3405   ultimately show ?thesis by auto
```
```  3406 qed
```
```  3407
```
```  3408 lemma affine_dependent_iff_dependent:
```
```  3409   assumes "a \<notin> S"
```
```  3410   shows "affine_dependent (insert a S) \<longleftrightarrow> dependent ((\<lambda>x. -a + x) ` S)"
```
```  3411 proof -
```
```  3412   have "((+) (- a) ` S) = {x - a| x . x \<in> S}" by auto
```
```  3413   then show ?thesis
```
```  3414     using affine_dependent_translation_eq[of "(insert a S)" "-a"]
```
```  3415       affine_dependent_imp_dependent2 assms
```
```  3416       dependent_imp_affine_dependent[of a S]
```
```  3417     by (auto simp del: uminus_add_conv_diff)
```
```  3418 qed
```
```  3419
```
```  3420 lemma affine_dependent_iff_dependent2:
```
```  3421   assumes "a \<in> S"
```
```  3422   shows "affine_dependent S \<longleftrightarrow> dependent ((\<lambda>x. -a + x) ` (S-{a}))"
```
```  3423 proof -
```
```  3424   have "insert a (S - {a}) = S"
```
```  3425     using assms by auto
```
```  3426   then show ?thesis
```
```  3427     using assms affine_dependent_iff_dependent[of a "S-{a}"] by auto
```
```  3428 qed
```
```  3429
```
```  3430 lemma affine_hull_insert_span_gen:
```
```  3431   "affine hull (insert a s) = (\<lambda>x. a + x) ` span ((\<lambda>x. - a + x) ` s)"
```
```  3432 proof -
```
```  3433   have h1: "{x - a |x. x \<in> s} = ((\<lambda>x. -a+x) ` s)"
```
```  3434     by auto
```
```  3435   {
```
```  3436     assume "a \<notin> s"
```
```  3437     then have ?thesis
```
```  3438       using affine_hull_insert_span[of a s] h1 by auto
```
```  3439   }
```
```  3440   moreover
```
```  3441   {
```
```  3442     assume a1: "a \<in> s"
```
```  3443     have "\<exists>x. x \<in> s \<and> -a+x=0"
```
```  3444       apply (rule exI[of _ a])
```
```  3445       using a1
```
```  3446       apply auto
```
```  3447       done
```
```  3448     then have "insert 0 ((\<lambda>x. -a+x) ` (s - {a})) = (\<lambda>x. -a+x) ` s"
```
```  3449       by auto
```
```  3450     then have "span ((\<lambda>x. -a+x) ` (s - {a}))=span ((\<lambda>x. -a+x) ` s)"
```
```  3451       using span_insert_0[of "(+) (- a) ` (s - {a})"] by (auto simp del: uminus_add_conv_diff)
```
```  3452     moreover have "{x - a |x. x \<in> (s - {a})} = ((\<lambda>x. -a+x) ` (s - {a}))"
```
```  3453       by auto
```
```  3454     moreover have "insert a (s - {a}) = insert a s"
```
```  3455       by auto
```
```  3456     ultimately have ?thesis
```
```  3457       using affine_hull_insert_span[of "a" "s-{a}"] by auto
```
```  3458   }
```
```  3459   ultimately show ?thesis by auto
```
```  3460 qed
```
```  3461
```
```  3462 lemma affine_hull_span2:
```
```  3463   assumes "a \<in> s"
```
```  3464   shows "affine hull s = (\<lambda>x. a+x) ` span ((\<lambda>x. -a+x) ` (s-{a}))"
```
```  3465   using affine_hull_insert_span_gen[of a "s - {a}", unfolded insert_Diff[OF assms]]
```
```  3466   by auto
```
```  3467
```
```  3468 lemma affine_hull_span_gen:
```
```  3469   assumes "a \<in> affine hull s"
```
```  3470   shows "affine hull s = (\<lambda>x. a+x) ` span ((\<lambda>x. -a+x) ` s)"
```
```  3471 proof -
```
```  3472   have "affine hull (insert a s) = affine hull s"
```
```  3473     using hull_redundant[of a affine s] assms by auto
```
```  3474   then show ?thesis
```
```  3475     using affine_hull_insert_span_gen[of a "s"] by auto
```
```  3476 qed
```
```  3477
```
```  3478 lemma affine_hull_span_0:
```
```  3479   assumes "0 \<in> affine hull S"
```
```  3480   shows "affine hull S = span S"
```
```  3481   using affine_hull_span_gen[of "0" S] assms by auto
```
```  3482
```
```  3483 lemma extend_to_affine_basis_nonempty:
```
```  3484   fixes S V :: "'n::euclidean_space set"
```
```  3485   assumes "\<not> affine_dependent S" "S \<subseteq> V" "S \<noteq> {}"
```
```  3486   shows "\<exists>T. \<not> affine_dependent T \<and> S \<subseteq> T \<and> T \<subseteq> V \<and> affine hull T = affine hull V"
```
```  3487 proof -
```
```  3488   obtain a where a: "a \<in> S"
```
```  3489     using assms by auto
```
```  3490   then have h0: "independent  ((\<lambda>x. -a + x) ` (S-{a}))"
```
```  3491     using affine_dependent_iff_dependent2 assms by auto
```
```  3492   then obtain B where B:
```
```  3493     "(\<lambda>x. -a+x) ` (S - {a}) \<subseteq> B \<and> B \<subseteq> (\<lambda>x. -a+x) ` V \<and> independent B \<and> (\<lambda>x. -a+x) ` V \<subseteq> span B"
```
```  3494      using maximal_independent_subset_extend[of "(\<lambda>x. -a+x) ` (S-{a})" "(\<lambda>x. -a + x) ` V"] assms
```
```  3495      by blast
```
```  3496   define T where "T = (\<lambda>x. a+x) ` insert 0 B"
```
```  3497   then have "T = insert a ((\<lambda>x. a+x) ` B)"
```
```  3498     by auto
```
```  3499   then have "affine hull T = (\<lambda>x. a+x) ` span B"
```
```  3500     using affine_hull_insert_span_gen[of a "((\<lambda>x. a+x) ` B)"] translation_assoc[of "-a" a B]
```
```  3501     by auto
```
```  3502   then have "V \<subseteq> affine hull T"
```
```  3503     using B assms translation_inverse_subset[of a V "span B"]
```
```  3504     by auto
```
```  3505   moreover have "T \<subseteq> V"
```
```  3506     using T_def B a assms by auto
```
```  3507   ultimately have "affine hull T = affine hull V"
```
```  3508     by (metis Int_absorb1 Int_absorb2 hull_hull hull_mono)
```
```  3509   moreover have "S \<subseteq> T"
```
```  3510     using T_def B translation_inverse_subset[of a "S-{a}" B]
```
```  3511     by auto
```
```  3512   moreover have "\<not> affine_dependent T"
```
```  3513     using T_def affine_dependent_translation_eq[of "insert 0 B"]
```
```  3514       affine_dependent_imp_dependent2 B
```
```  3515     by auto
```
```  3516   ultimately show ?thesis using \<open>T \<subseteq> V\<close> by auto
```
```  3517 qed
```
```  3518
```
```  3519 lemma affine_basis_exists:
```
```  3520   fixes V :: "'n::euclidean_space set"
```
```  3521   shows "\<exists>B. B \<subseteq> V \<and> \<not> affine_dependent B \<and> affine hull V = affine hull B"
```
```  3522 proof (cases "V = {}")
```
```  3523   case True
```
```  3524   then show ?thesis
```
```  3525     using affine_independent_0 by auto
```
```  3526 next
```
```  3527   case False
```
```  3528   then obtain x where "x \<in> V" by auto
```
```  3529   then show ?thesis
```
```  3530     using affine_dependent_def[of "{x}"] extend_to_affine_basis_nonempty[of "{x}" V]
```
```  3531     by auto
```
```  3532 qed
```
```  3533
```
```  3534 proposition extend_to_affine_basis:
```
```  3535   fixes S V :: "'n::euclidean_space set"
```
```  3536   assumes "\<not> affine_dependent S" "S \<subseteq> V"
```
```  3537   obtains T where "\<not> affine_dependent T" "S \<subseteq> T" "T \<subseteq> V" "affine hull T = affine hull V"
```
```  3538 proof (cases "S = {}")
```
```  3539   case True then show ?thesis
```
```  3540     using affine_basis_exists by (metis empty_subsetI that)
```
```  3541 next
```
```  3542   case False
```
```  3543   then show ?thesis by (metis assms extend_to_affine_basis_nonempty that)
```
```  3544 qed
```
```  3545
```
```  3546
```
```  3547 subsection \<open>Affine Dimension of a Set\<close>
```
```  3548
```
```  3549 definition%important aff_dim :: "('a::euclidean_space) set \<Rightarrow> int"
```
```  3550   where "aff_dim V =
```
```  3551   (SOME d :: int.
```
```  3552     \<exists>B. affine hull B = affine hull V \<and> \<not> affine_dependent B \<and> of_nat (card B) = d + 1)"
```
```  3553
```
```  3554 lemma aff_dim_basis_exists:
```
```  3555   fixes V :: "('n::euclidean_space) set"
```
```  3556   shows "\<exists>B. affine hull B = affine hull V \<and> \<not> affine_dependent B \<and> of_nat (card B) = aff_dim V + 1"
```
```  3557 proof -
```
```  3558   obtain B where "\<not> affine_dependent B \<and> affine hull B = affine hull V"
```
```  3559     using affine_basis_exists[of V] by auto
```
```  3560   then show ?thesis
```
```  3561     unfolding aff_dim_def
```
```  3562       some_eq_ex[of "\<lambda>d. \<exists>B. affine hull B = affine hull V \<and> \<not> affine_dependent B \<and> of_nat (card B) = d + 1"]
```
```  3563     apply auto
```
```  3564     apply (rule exI[of _ "int (card B) - (1 :: int)"])
```
```  3565     apply (rule exI[of _ "B"])
```
```  3566     apply auto
```
```  3567     done
```
```  3568 qed
```
```  3569
```
```  3570 lemma affine_hull_nonempty: "S \<noteq> {} \<longleftrightarrow> affine hull S \<noteq> {}"
```
```  3571 proof -
```
```  3572   have "S = {} \<Longrightarrow> affine hull S = {}"
```
```  3573     using affine_hull_empty by auto
```
```  3574   moreover have "affine hull S = {} \<Longrightarrow> S = {}"
```
```  3575     unfolding hull_def by auto
```
```  3576   ultimately show ?thesis by blast
```
```  3577 qed
```
```  3578
```
```  3579 lemma aff_dim_parallel_subspace_aux:
```
```  3580   fixes B :: "'n::euclidean_space set"
```
```  3581   assumes "\<not> affine_dependent B" "a \<in> B"
```
```  3582   shows "finite B \<and> ((card B) - 1 = dim (span ((\<lambda>x. -a+x) ` (B-{a}))))"
```
```  3583 proof -
```
```  3584   have "independent ((\<lambda>x. -a + x) ` (B-{a}))"
```
```  3585     using affine_dependent_iff_dependent2 assms by auto
```
```  3586   then have fin: "dim (span ((\<lambda>x. -a+x) ` (B-{a}))) = card ((\<lambda>x. -a + x) ` (B-{a}))"
```
```  3587     "finite ((\<lambda>x. -a + x) ` (B - {a}))"
```
```  3588     using indep_card_eq_dim_span[of "(\<lambda>x. -a+x) ` (B-{a})"] by auto
```
```  3589   show ?thesis
```
```  3590   proof (cases "(\<lambda>x. -a + x) ` (B - {a}) = {}")
```
```  3591     case True
```
```  3592     have "B = insert a ((\<lambda>x. a + x) ` (\<lambda>x. -a + x) ` (B - {a}))"
```
```  3593       using translation_assoc[of "a" "-a" "(B - {a})"] assms by auto
```
```  3594     then have "B = {a}" using True by auto
```
```  3595     then show ?thesis using assms fin by auto
```
```  3596   next
```
```  3597     case False
```
```  3598     then have "card ((\<lambda>x. -a + x) ` (B - {a})) > 0"
```
```  3599       using fin by auto
```
```  3600     moreover have h1: "card ((\<lambda>x. -a + x) ` (B-{a})) = card (B-{a})"
```
```  3601        apply (rule card_image)
```
```  3602        using translate_inj_on
```
```  3603        apply (auto simp del: uminus_add_conv_diff)
```
```  3604        done
```
```  3605     ultimately have "card (B-{a}) > 0" by auto
```
```  3606     then have *: "finite (B - {a})"
```
```  3607       using card_gt_0_iff[of "(B - {a})"] by auto
```
```  3608     then have "card (B - {a}) = card B - 1"
```
```  3609       using card_Diff_singleton assms by auto
```
```  3610     with * show ?thesis using fin h1 by auto
```
```  3611   qed
```
```  3612 qed
```
```  3613
```
```  3614 lemma aff_dim_parallel_subspace:
```
```  3615   fixes V L :: "'n::euclidean_space set"
```
```  3616   assumes "V \<noteq> {}"
```
```  3617     and "subspace L"
```
```  3618     and "affine_parallel (affine hull V) L"
```
```  3619   shows "aff_dim V = int (dim L)"
```
```  3620 proof -
```
```  3621   obtain B where
```
```  3622     B: "affine hull B = affine hull V \<and> \<not> affine_dependent B \<and> int (card B) = aff_dim V + 1"
```
```  3623     using aff_dim_basis_exists by auto
```
```  3624   then have "B \<noteq> {}"
```
```  3625     using assms B affine_hull_nonempty[of V] affine_hull_nonempty[of B]
```
```  3626     by auto
```
```  3627   then obtain a where a: "a \<in> B" by auto
```
```  3628   define Lb where "Lb = span ((\<lambda>x. -a+x) ` (B-{a}))"
```
```  3629   moreover have "affine_parallel (affine hull B) Lb"
```
```  3630     using Lb_def B assms affine_hull_span2[of a B] a
```
```  3631       affine_parallel_commut[of "Lb" "(affine hull B)"]
```
```  3632     unfolding affine_parallel_def
```
```  3633     by auto
```
```  3634   moreover have "subspace Lb"
```
```  3635     using Lb_def subspace_span by auto
```
```  3636   moreover have "affine hull B \<noteq> {}"
```
```  3637     using assms B affine_hull_nonempty[of V] by auto
```
```  3638   ultimately have "L = Lb"
```
```  3639     using assms affine_parallel_subspace[of "affine hull B"] affine_affine_hull[of B] B
```
```  3640     by auto
```
```  3641   then have "dim L = dim Lb"
```
```  3642     by auto
```
```  3643   moreover have "card B - 1 = dim Lb" and "finite B"
```
```  3644     using Lb_def aff_dim_parallel_subspace_aux a B by auto
```
```  3645   ultimately show ?thesis
```
```  3646     using B \<open>B \<noteq> {}\<close> card_gt_0_iff[of B] by auto
```
```  3647 qed
```
```  3648
```
```  3649 lemma aff_independent_finite:
```
```  3650   fixes B :: "'n::euclidean_space set"
```
```  3651   assumes "\<not> affine_dependent B"
```
```  3652   shows "finite B"
```
```  3653 proof -
```
```  3654   {
```
```  3655     assume "B \<noteq> {}"
```
```  3656     then obtain a where "a \<in> B" by auto
```
```  3657     then have ?thesis
```
```  3658       using aff_dim_parallel_subspace_aux assms by auto
```
```  3659   }
```
```  3660   then show ?thesis by auto
```
```  3661 qed
```
```  3662
```
```  3663 lemma independent_finite:
```
```  3664   fixes B :: "'n::euclidean_space set"
```
```  3665   assumes "independent B"
```
```  3666   shows "finite B"
```
```  3667   using affine_dependent_imp_dependent[of B] aff_independent_finite[of B] assms
```
```  3668   by auto
```
```  3669
```
```  3670 lemma subspace_dim_equal:
```
```  3671   assumes "subspace (S :: ('n::euclidean_space) set)"
```
```  3672     and "subspace T"
```
```  3673     and "S \<subseteq> T"
```
```  3674     and "dim S \<ge> dim T"
```
```  3675   shows "S = T"
```
```  3676 proof -
```
```  3677   obtain B where B: "B \<le> S" "independent B \<and> S \<subseteq> span B" "card B = dim S"
```
```  3678     using basis_exists[of S] by auto
```
```  3679   then have "span B \<subseteq> S"
```
```  3680     using span_mono[of B S] span_eq[of S] assms by metis
```
```  3681   then have "span B = S"
```
```  3682     using B by auto
```
```  3683   have "dim S = dim T"
```
```  3684     using assms dim_subset[of S T] by auto
```
```  3685   then have "T \<subseteq> span B"
```
```  3686     using card_eq_dim[of B T] B independent_finite assms by auto
```
```  3687   then show ?thesis
```
```  3688     using assms \<open>span B = S\<close> by auto
```
```  3689 qed
```
```  3690
```
```  3691 corollary dim_eq_span:
```
```  3692   fixes S :: "'a::euclidean_space set"
```
```  3693   shows "\<lbrakk>S \<subseteq> T; dim T \<le> dim S\<rbrakk> \<Longrightarrow> span S = span T"
```
```  3694 by (simp add: span_mono subspace_dim_equal subspace_span)
```
```  3695
```
```  3696 lemma dim_eq_full:
```
```  3697     fixes S :: "'a :: euclidean_space set"
```
```  3698     shows "dim S = DIM('a) \<longleftrightarrow> span S = UNIV"
```
```  3699 apply (rule iffI)
```
```  3700  apply (metis dim_eq_span dim_subset_UNIV span_Basis span_span subset_UNIV)
```
```  3701 by (metis dim_UNIV dim_span)
```
```  3702
```
```  3703 lemma span_substd_basis:
```
```  3704   assumes d: "d \<subseteq> Basis"
```
```  3705   shows "span d = {x. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x\<bullet>i = 0}"
```
```  3706   (is "_ = ?B")
```
```  3707 proof -
```
```  3708   have "d \<subseteq> ?B"
```
```  3709     using d by (auto simp: inner_Basis)
```
```  3710   moreover have s: "subspace ?B"
```
```  3711     using subspace_substandard[of "\<lambda>i. i \<notin> d"] .
```
```  3712   ultimately have "span d \<subseteq> ?B"
```
```  3713     using span_mono[of d "?B"] span_eq[of "?B"] by blast
```
```  3714   moreover have *: "card d \<le> dim (span d)"
```
```  3715     using independent_card_le_dim[of d "span d"] independent_substdbasis[OF assms] span_inc[of d]
```
```  3716     by auto
```
```  3717   moreover from * have "dim ?B \<le> dim (span d)"
```
```  3718     using dim_substandard[OF assms] by auto
```
```  3719   ultimately show ?thesis
```
```  3720     using s subspace_dim_equal[of "span d" "?B"] subspace_span[of d] by auto
```
```  3721 qed
```
```  3722
```
```  3723 lemma basis_to_substdbasis_subspace_isomorphism:
```
```  3724   fixes B :: "'a::euclidean_space set"
```
```  3725   assumes "independent B"
```
```  3726   shows "\<exists>f d::'a set. card d = card B \<and> linear f \<and> f ` B = d \<and>
```
```  3727     f ` span B = {x. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x \<bullet> i = 0} \<and> inj_on f (span B) \<and> d \<subseteq> Basis"
```
```  3728 proof -
```
```  3729   have B: "card B = dim B"
```
```  3730     using dim_unique[of B B "card B"] assms span_inc[of B] by auto
```
```  3731   have "dim B \<le> card (Basis :: 'a set)"
```
```  3732     using dim_subset_UNIV[of B] by simp
```
```  3733   from ex_card[OF this] obtain d :: "'a set" where d: "d \<subseteq> Basis" and t: "card d = dim B"
```
```  3734     by auto
```
```  3735   let ?t = "{x::'a::euclidean_space. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x\<bullet>i = 0}"
```
```  3736   have "\<exists>f. linear f \<and> f ` B = d \<and> f ` span B = ?t \<and> inj_on f (span B)"
```
```  3737     apply (rule basis_to_basis_subspace_isomorphism[of "span B" ?t B "d"])
```
```  3738     apply (rule subspace_span)
```
```  3739     apply (rule subspace_substandard)
```
```  3740     defer
```
```  3741     apply (rule span_inc)
```
```  3742     apply (rule assms)
```
```  3743     defer
```
```  3744     unfolding dim_span[of B]
```
```  3745     apply(rule B)
```
```  3746     unfolding span_substd_basis[OF d, symmetric]
```
```  3747     apply (rule span_inc)
```
```  3748     apply (rule independent_substdbasis[OF d])
```
```  3749     apply rule
```
```  3750     apply assumption
```
```  3751     unfolding t[symmetric] span_substd_basis[OF d] dim_substandard[OF d]
```
```  3752     apply auto
```
```  3753     done
```
```  3754   with t \<open>card B = dim B\<close> d show ?thesis by auto
```
```  3755 qed
```
```  3756
```
```  3757 lemma aff_dim_empty:
```
```  3758   fixes S :: "'n::euclidean_space set"
```
```  3759   shows "S = {} \<longleftrightarrow> aff_dim S = -1"
```
```  3760 proof -
```
```  3761   obtain B where *: "affine hull B = affine hull S"
```
```  3762     and "\<not> affine_dependent B"
```
```  3763     and "int (card B) = aff_dim S + 1"
```
```  3764     using aff_dim_basis_exists by auto
```
```  3765   moreover
```
```  3766   from * have "S = {} \<longleftrightarrow> B = {}"
```
```  3767     using affine_hull_nonempty[of B] affine_hull_nonempty[of S] by auto
```
```  3768   ultimately show ?thesis
```
```  3769     using aff_independent_finite[of B] card_gt_0_iff[of B] by auto
```
```  3770 qed
```
```  3771
```
```  3772 lemma aff_dim_empty_eq [simp]: "aff_dim ({}::'a::euclidean_space set) = -1"
```
```  3773   by (simp add: aff_dim_empty [symmetric])
```
```  3774
```
```  3775 lemma aff_dim_affine_hull [simp]: "aff_dim (affine hull S) = aff_dim S"
```
```  3776   unfolding aff_dim_def using hull_hull[of _ S] by auto
```
```  3777
```
```  3778 lemma aff_dim_affine_hull2:
```
```  3779   assumes "affine hull S = affine hull T"
```
```  3780   shows "aff_dim S = aff_dim T"
```
```  3781   unfolding aff_dim_def using assms by auto
```
```  3782
```
```  3783 lemma aff_dim_unique:
```
```  3784   fixes B V :: "'n::euclidean_space set"
```
```  3785   assumes "affine hull B = affine hull V \<and> \<not> affine_dependent B"
```
```  3786   shows "of_nat (card B) = aff_dim V + 1"
```
```  3787 proof (cases "B = {}")
```
```  3788   case True
```
```  3789   then have "V = {}"
```
```  3790     using affine_hull_nonempty[of V] affine_hull_nonempty[of B] assms
```
```  3791     by auto
```
```  3792   then have "aff_dim V = (-1::int)"
```
```  3793     using aff_dim_empty by auto
```
```  3794   then show ?thesis
```
```  3795     using \<open>B = {}\<close> by auto
```
```  3796 next
```
```  3797   case False
```
```  3798   then obtain a where a: "a \<in> B" by auto
```
```  3799   define Lb where "Lb = span ((\<lambda>x. -a+x) ` (B-{a}))"
```
```  3800   have "affine_parallel (affine hull B) Lb"
```
```  3801     using Lb_def affine_hull_span2[of a B] a
```
```  3802       affine_parallel_commut[of "Lb" "(affine hull B)"]
```
```  3803     unfolding affine_parallel_def by auto
```
```  3804   moreover have "subspace Lb"
```
```  3805     using Lb_def subspace_span by auto
```
```  3806   ultimately have "aff_dim B = int(dim Lb)"
```
```  3807     using aff_dim_parallel_subspace[of B Lb] \<open>B \<noteq> {}\<close> by auto
```
```  3808   moreover have "(card B) - 1 = dim Lb" "finite B"
```
```  3809     using Lb_def aff_dim_parallel_subspace_aux a assms by auto
```
```  3810   ultimately have "of_nat (card B) = aff_dim B + 1"
```
```  3811     using \<open>B \<noteq> {}\<close> card_gt_0_iff[of B] by auto
```
```  3812   then show ?thesis
```
```  3813     using aff_dim_affine_hull2 assms by auto
```
```  3814 qed
```
```  3815
```
```  3816 lemma aff_dim_affine_independent:
```
```  3817   fixes B :: "'n::euclidean_space set"
```
```  3818   assumes "\<not> affine_dependent B"
```
```  3819   shows "of_nat (card B) = aff_dim B + 1"
```
```  3820   using aff_dim_unique[of B B] assms by auto
```
```  3821
```
```  3822 lemma affine_independent_iff_card:
```
```  3823     fixes s :: "'a::euclidean_space set"
```
```  3824     shows "~ affine_dependent s \<longleftrightarrow> finite s \<and> aff_dim s = int(card s) - 1"
```
```  3825   apply (rule iffI)
```
```  3826   apply (simp add: aff_dim_affine_independent aff_independent_finite)
```
```  3827   by (metis affine_basis_exists [of s] aff_dim_unique card_subset_eq diff_add_cancel of_nat_eq_iff)
```
```  3828
```
```  3829 lemma aff_dim_sing [simp]:
```
```  3830   fixes a :: "'n::euclidean_space"
```
```  3831   shows "aff_dim {a} = 0"
```
```  3832   using aff_dim_affine_independent[of "{a}"] affine_independent_1 by auto
```
```  3833
```
```  3834 lemma aff_dim_2 [simp]: "aff_dim {a,b} = (if a = b then 0 else 1)"
```
```  3835 proof (clarsimp)
```
```  3836   assume "a \<noteq> b"
```
```  3837   then have "aff_dim{a,b} = card{a,b} - 1"
```
```  3838     using affine_independent_2 [of a b] aff_dim_affine_independent by fastforce
```
```  3839   also have "... = 1"
```
```  3840     using \<open>a \<noteq> b\<close> by simp
```
```  3841   finally show "aff_dim {a, b} = 1" .
```
```  3842 qed
```
```  3843
```
```  3844 lemma aff_dim_inner_basis_exists:
```
```  3845   fixes V :: "('n::euclidean_space) set"
```
```  3846   shows "\<exists>B. B \<subseteq> V \<and> affine hull B = affine hull V \<and>
```
```  3847     \<not> affine_dependent B \<and> of_nat (card B) = aff_dim V + 1"
```
```  3848 proof -
```
```  3849   obtain B where B: "\<not> affine_dependent B" "B \<subseteq> V" "affine hull B = affine hull V"
```
```  3850     using affine_basis_exists[of V] by auto
```
```  3851   then have "of_nat(card B) = aff_dim V+1" using aff_dim_unique by auto
```
```  3852   with B show ?thesis by auto
```
```  3853 qed
```
```  3854
```
```  3855 lemma aff_dim_le_card:
```
```  3856   fixes V :: "'n::euclidean_space set"
```
```  3857   assumes "finite V"
```
```  3858   shows "aff_dim V \<le> of_nat (card V) - 1"
```
```  3859 proof -
```
```  3860   obtain B where B: "B \<subseteq> V" "of_nat (card B) = aff_dim V + 1"
```
```  3861     using aff_dim_inner_basis_exists[of V] by auto
```
```  3862   then have "card B \<le> card V"
```
```  3863     using assms card_mono by auto
```
```  3864   with B show ?thesis by auto
```
```  3865 qed
```
```  3866
```
```  3867 lemma aff_dim_parallel_eq:
```
```  3868   fixes S T :: "'n::euclidean_space set"
```
```  3869   assumes "affine_parallel (affine hull S) (affine hull T)"
```
```  3870   shows "aff_dim S = aff_dim T"
```
```  3871 proof -
```
```  3872   {
```
```  3873     assume "T \<noteq> {}" "S \<noteq> {}"
```
```  3874     then obtain L where L: "subspace L \<and> affine_parallel (affine hull T) L"
```
```  3875       using affine_parallel_subspace[of "affine hull T"]
```
```  3876         affine_affine_hull[of T] affine_hull_nonempty
```
```  3877       by auto
```
```  3878     then have "aff_dim T = int (dim L)"
```
```  3879       using aff_dim_parallel_subspace \<open>T \<noteq> {}\<close> by auto
```
```  3880     moreover have *: "subspace L \<and> affine_parallel (affine hull S) L"
```
```  3881        using L affine_parallel_assoc[of "affine hull S" "affine hull T" L] assms by auto
```
```  3882     moreover from * have "aff_dim S = int (dim L)"
```
```  3883       using aff_dim_parallel_subspace \<open>S \<noteq> {}\<close> by auto
```
```  3884     ultimately have ?thesis by auto
```
```  3885   }
```
```  3886   moreover
```
```  3887   {
```
```  3888     assume "S = {}"
```
```  3889     then have "S = {}" and "T = {}"
```
```  3890       using assms affine_hull_nonempty
```
```  3891       unfolding affine_parallel_def
```
```  3892       by auto
```
```  3893     then have ?thesis using aff_dim_empty by auto
```
```  3894   }
```
```  3895   moreover
```
```  3896   {
```
```  3897     assume "T = {}"
```
```  3898     then have "S = {}" and "T = {}"
```
```  3899       using assms affine_hull_nonempty
```
```  3900       unfolding affine_parallel_def
```
```  3901       by auto
```
```  3902     then have ?thesis
```
```  3903       using aff_dim_empty by auto
```
```  3904   }
```
```  3905   ultimately show ?thesis by blast
```
```  3906 qed
```
```  3907
```
```  3908 lemma aff_dim_translation_eq:
```
```  3909   fixes a :: "'n::euclidean_space"
```
```  3910   shows "aff_dim ((\<lambda>x. a + x) ` S) = aff_dim S"
```
```  3911 proof -
```
```  3912   have "affine_parallel (affine hull S) (affine hull ((\<lambda>x. a + x) ` S))"
```
```  3913     unfolding affine_parallel_def
```
```  3914     apply (rule exI[of _ "a"])
```
```  3915     using affine_hull_translation[of a S]
```
```  3916     apply auto
```
```  3917     done
```
```  3918   then show ?thesis
```
```  3919     using aff_dim_parallel_eq[of S "(\<lambda>x. a + x) ` S"] by auto
```
```  3920 qed
```
```  3921
```
```  3922 lemma aff_dim_affine:
```
```  3923   fixes S L :: "'n::euclidean_space set"
```
```  3924   assumes "S \<noteq> {}"
```
```  3925     and "affine S"
```
```  3926     and "subspace L"
```
```  3927     and "affine_parallel S L"
```
```  3928   shows "aff_dim S = int (dim L)"
```
```  3929 proof -
```
```  3930   have *: "affine hull S = S"
```
```  3931     using assms affine_hull_eq[of S] by auto
```
```  3932   then have "affine_parallel (affine hull S) L"
```
```  3933     using assms by (simp add: *)
```
```  3934   then show ?thesis
```
```  3935     using assms aff_dim_parallel_subspace[of S L] by blast
```
```  3936 qed
```
```  3937
```
```  3938 lemma dim_affine_hull:
```
```  3939   fixes S :: "'n::euclidean_space set"
```
```  3940   shows "dim (affine hull S) = dim S"
```
```  3941 proof -
```
```  3942   have "dim (affine hull S) \<ge> dim S"
```
```  3943     using dim_subset by auto
```
```  3944   moreover have "dim (span S) \<ge> dim (affine hull S)"
```
```  3945     using dim_subset affine_hull_subset_span by blast
```
```  3946   moreover have "dim (span S) = dim S"
```
```  3947     using dim_span by auto
```
```  3948   ultimately show ?thesis by auto
```
```  3949 qed
```
```  3950
```
```  3951 lemma aff_dim_subspace:
```
```  3952   fixes S :: "'n::euclidean_space set"
```
```  3953   assumes "subspace S"
```
```  3954   shows "aff_dim S = int (dim S)"
```
```  3955 proof (cases "S={}")
```
```  3956   case True with assms show ?thesis
```
```  3957     by (simp add: subspace_affine)
```
```  3958 next
```
```  3959   case False
```
```  3960   with aff_dim_affine[of S S] assms subspace_imp_affine[of S] affine_parallel_reflex[of S] subspace_affine
```
```  3961   show ?thesis by auto
```
```  3962 qed
```
```  3963
```
```  3964 lemma aff_dim_zero:
```
```  3965   fixes S :: "'n::euclidean_space set"
```
```  3966   assumes "0 \<in> affine hull S"
```
```  3967   shows "aff_dim S = int (dim S)"
```
```  3968 proof -
```
```  3969   have "subspace (affine hull S)"
```
```  3970     using subspace_affine[of "affine hull S"] affine_affine_hull assms
```
```  3971     by auto
```
```  3972   then have "aff_dim (affine hull S) = int (dim (affine hull S))"
```
```  3973     using assms aff_dim_subspace[of "affine hull S"] by auto
```
```  3974   then show ?thesis
```
```  3975     using aff_dim_affine_hull[of S] dim_affine_hull[of S]
```
```  3976     by auto
```
```  3977 qed
```
```  3978
```
```  3979 lemma aff_dim_eq_dim:
```
```  3980   fixes S :: "'n::euclidean_space set"
```
```  3981   assumes "a \<in> affine hull S"
```
```  3982   shows "aff_dim S = int (dim ((\<lambda>x. -a+x) ` S))"
```
```  3983 proof -
```
```  3984   have "0 \<in> affine hull ((\<lambda>x. -a+x) ` S)"
```
```  3985     unfolding Convex_Euclidean_Space.affine_hull_translation
```
```  3986     using assms by (simp add: ab_group_add_class.ab_left_minus image_iff)
```
```  3987   with aff_dim_zero show ?thesis
```
```  3988     by (metis aff_dim_translation_eq)
```
```  3989 qed
```
```  3990
```
```  3991 lemma aff_dim_UNIV [simp]: "aff_dim (UNIV :: 'n::euclidean_space set) = int(DIM('n))"
```
```  3992   using aff_dim_subspace[of "(UNIV :: 'n::euclidean_space set)"]
```
```  3993     dim_UNIV[where 'a="'n::euclidean_space"]
```
```  3994   by auto
```
```  3995
```
```  3996 lemma aff_dim_geq:
```
```  3997   fixes V :: "'n::euclidean_space set"
```
```  3998   shows "aff_dim V \<ge> -1"
```
```  3999 proof -
```
```  4000   obtain B where "affine hull B = affine hull V"
```
```  4001     and "\<not> affine_dependent B"
```
```  4002     and "int (card B) = aff_dim V + 1"
```
```  4003     using aff_dim_basis_exists by auto
```
```  4004   then show ?thesis by auto
```
```  4005 qed
```
```  4006
```
```  4007 lemma aff_dim_negative_iff [simp]:
```
```  4008   fixes S :: "'n::euclidean_space set"
```
```  4009   shows "aff_dim S < 0 \<longleftrightarrow>S = {}"
```
```  4010 by (metis aff_dim_empty aff_dim_geq diff_0 eq_iff zle_diff1_eq)
```
```  4011
```
```  4012 lemma aff_lowdim_subset_hyperplane:
```
```  4013   fixes S :: "'a::euclidean_space set"
```
```  4014   assumes "aff_dim S < DIM('a)"
```
```  4015   obtains a b where "a \<noteq> 0" "S \<subseteq> {x. a \<bullet> x = b}"
```
```  4016 proof (cases "S={}")
```
```  4017   case True
```
```  4018   moreover
```
```  4019   have "(SOME b. b \<in> Basis) \<noteq> 0"
```
```  4020     by (metis norm_some_Basis norm_zero zero_neq_one)
```
```  4021   ultimately show ?thesis
```
```  4022     using that by blast
```
```  4023 next
```
```  4024   case False
```
```  4025   then obtain c S' where "c \<notin> S'" "S = insert c S'"
```
```  4026     by (meson equals0I mk_disjoint_insert)
```
```  4027   have "dim ((+) (-c) ` S) < DIM('a)"
```
```  4028     by (metis \<open>S = insert c S'\<close> aff_dim_eq_dim assms hull_inc insertI1 of_nat_less_imp_less)
```
```  4029   then obtain a where "a \<noteq> 0" "span ((+) (-c) ` S) \<subseteq> {x. a \<bullet> x = 0}"
```
```  4030     using lowdim_subset_hyperplane by blast
```
```  4031   moreover
```
```  4032   have "a \<bullet> w = a \<bullet> c" if "span ((+) (- c) ` S) \<subseteq> {x. a \<bullet> x = 0}" "w \<in> S" for w
```
```  4033   proof -
```
```  4034     have "w-c \<in> span ((+) (- c) ` S)"
```
```  4035       by (simp add: span_superset \<open>w \<in> S\<close>)
```
```  4036     with that have "w-c \<in> {x. a \<bullet> x = 0}"
```
```  4037       by blast
```
```  4038     then show ?thesis
```
```  4039       by (auto simp: algebra_simps)
```
```  4040   qed
```
```  4041   ultimately have "S \<subseteq> {x. a \<bullet> x = a \<bullet> c}"
```
```  4042     by blast
```
```  4043   then show ?thesis
```
```  4044     by (rule that[OF \<open>a \<noteq> 0\<close>])
```
```  4045 qed
```
```  4046
```
```  4047 lemma affine_independent_card_dim_diffs:
```
```  4048   fixes S :: "'a :: euclidean_space set"
```
```  4049   assumes "~ affine_dependent S" "a \<in> S"
```
```  4050     shows "card S = dim {x - a|x. x \<in> S} + 1"
```
```  4051 proof -
```
```  4052   have 1: "{b - a|b. b \<in> (S - {a})} \<subseteq> {x - a|x. x \<in> S}" by auto
```
```  4053   have 2: "x - a \<in> span {b - a |b. b \<in> S - {a}}" if "x \<in> S" for x
```
```  4054   proof (cases "x = a")
```
```  4055     case True then show ?thesis by simp
```
```  4056   next
```
```  4057     case False then show ?thesis
```
```  4058       using assms by (blast intro: span_superset that)
```
```  4059   qed
```
```  4060   have "\<not> affine_dependent (insert a S)"
```
```  4061     by (simp add: assms insert_absorb)
```
```  4062   then have 3: "independent {b - a |b. b \<in> S - {a}}"
```
```  4063       using dependent_imp_affine_dependent by fastforce
```
```  4064   have "{b - a |b. b \<in> S - {a}} = (\<lambda>b. b-a) ` (S - {a})"
```
```  4065     by blast
```
```  4066   then have "card {b - a |b. b \<in> S - {a}} = card ((\<lambda>b. b-a) ` (S - {a}))"
```
```  4067     by simp
```
```  4068   also have "... = card (S - {a})"
```
```  4069     by (metis (no_types, lifting) card_image diff_add_cancel inj_onI)
```
```  4070   also have "... = card S - 1"
```
```  4071     by (simp add: aff_independent_finite assms)
```
```  4072   finally have 4: "card {b - a |b. b \<in> S - {a}} = card S - 1" .
```
```  4073   have "finite S"
```
```  4074     by (meson assms aff_independent_finite)
```
```  4075   with \<open>a \<in> S\<close> have "card S \<noteq> 0" by auto
```
```  4076   moreover have "dim {x - a |x. x \<in> S} = card S - 1"
```
```  4077     using 2 by (blast intro: dim_unique [OF 1 _ 3 4])
```
```  4078   ultimately show ?thesis
```
```  4079     by auto
```
```  4080 qed
```
```  4081
```
```  4082 lemma independent_card_le_aff_dim:
```
```  4083   fixes B :: "'n::euclidean_space set"
```
```  4084   assumes "B \<subseteq> V"
```
```  4085   assumes "\<not> affine_dependent B"
```
```  4086   shows "int (card B) \<le> aff_dim V + 1"
```
```  4087 proof -
```
```  4088   obtain T where T: "\<not> affine_dependent T \<and> B \<subseteq> T \<and> T \<subseteq> V \<and> affine hull T = affine hull V"
```
```  4089     by (metis assms extend_to_affine_basis[of B V])
```
```  4090   then have "of_nat (card T) = aff_dim V + 1"
```
```  4091     using aff_dim_unique by auto
```
```  4092   then show ?thesis
```
```  4093     using T card_mono[of T B] aff_independent_finite[of T] by auto
```
```  4094 qed
```
```  4095
```
```  4096 lemma aff_dim_subset:
```
```  4097   fixes S T :: "'n::euclidean_space set"
```
```  4098   assumes "S \<subseteq> T"
```
```  4099   shows "aff_dim S \<le> aff_dim T"
```
```  4100 proof -
```
```  4101   obtain B where B: "\<not> affine_dependent B" "B \<subseteq> S" "affine hull B = affine hull S"
```
```  4102     "of_nat (card B) = aff_dim S + 1"
```
```  4103     using aff_dim_inner_basis_exists[of S] by auto
```
```  4104   then have "int (card B) \<le> aff_dim T + 1"
```
```  4105     using assms independent_card_le_aff_dim[of B T] by auto
```
```  4106   with B show ?thesis by auto
```
```  4107 qed
```
```  4108
```
```  4109 lemma aff_dim_le_DIM:
```
```  4110   fixes S :: "'n::euclidean_space set"
```
```  4111   shows "aff_dim S \<le> int (DIM('n))"
```
```  4112 proof -
```
```  4113   have "aff_dim (UNIV :: 'n::euclidean_space set) = int(DIM('n))"
```
```  4114     using aff_dim_UNIV by auto
```
```  4115   then show "aff_dim (S:: 'n::euclidean_space set) \<le> int(DIM('n))"
```
```  4116     using aff_dim_subset[of S "(UNIV :: ('n::euclidean_space) set)"] subset_UNIV by auto
```
```  4117 qed
```
```  4118
```
```  4119 lemma affine_dim_equal:
```
```  4120   fixes S :: "'n::euclidean_space set"
```
```  4121   assumes "affine S" "affine T" "S \<noteq> {}" "S \<subseteq> T" "aff_dim S = aff_dim T"
```
```  4122   shows "S = T"
```
```  4123 proof -
```
```  4124   obtain a where "a \<in> S" using assms by auto
```
```  4125   then have "a \<in> T" using assms by auto
```
```  4126   define LS where "LS = {y. \<exists>x \<in> S. (-a) + x = y}"
```
```  4127   then have ls: "subspace LS" "affine_parallel S LS"
```
```  4128     using assms parallel_subspace_explicit[of S a LS] \<open>a \<in> S\<close> by auto
```
```  4129   then have h1: "int(dim LS) = aff_dim S"
```
```  4130     using assms aff_dim_affine[of S LS] by auto
```
```  4131   have "T \<noteq> {}" using assms by auto
```
```  4132   define LT where "LT = {y. \<exists>x \<in> T. (-a) + x = y}"
```
```  4133   then have lt: "subspace LT \<and> affine_parallel T LT"
```
```  4134     using assms parallel_subspace_explicit[of T a LT] \<open>a \<in> T\<close> by auto
```
```  4135   then have "int(dim LT) = aff_dim T"
```
```  4136     using assms aff_dim_affine[of T LT] \<open>T \<noteq> {}\<close> by auto
```
```  4137   then have "dim LS = dim LT"
```
```  4138     using h1 assms by auto
```
```  4139   moreover have "LS \<le> LT"
```
```  4140     using LS_def LT_def assms by auto
```
```  4141   ultimately have "LS = LT"
```
```  4142     using subspace_dim_equal[of LS LT] ls lt by auto
```
```  4143   moreover have "S = {x. \<exists>y \<in> LS. a+y=x}"
```
```  4144     using LS_def by auto
```
```  4145   moreover have "T = {x. \<exists>y \<in> LT. a+y=x}"
```
```  4146     using LT_def by auto
```
```  4147   ultimately show ?thesis by auto
```
```  4148 qed
```
```  4149
```
```  4150 lemma aff_dim_eq_0:
```
```  4151   fixes S :: "'a::euclidean_space set"
```
```  4152   shows "aff_dim S = 0 \<longleftrightarrow> (\<exists>a. S = {a})"
```
```  4153 proof (cases "S = {}")
```
```  4154   case True
```
```  4155   then show ?thesis
```
```  4156     by auto
```
```  4157 next
```
```  4158   case False
```
```  4159   then obtain a where "a \<in> S" by auto
```
```  4160   show ?thesis
```
```  4161   proof safe
```
```  4162     assume 0: "aff_dim S = 0"
```
```  4163     have "~ {a,b} \<subseteq> S" if "b \<noteq> a" for b
```
```  4164       by (metis "0" aff_dim_2 aff_dim_subset not_one_le_zero that)
```
```  4165     then show "\<exists>a. S = {a}"
```
```  4166       using \<open>a \<in> S\<close> by blast
```
```  4167   qed auto
```
```  4168 qed
```
```  4169
```
```  4170 lemma affine_hull_UNIV:
```
```  4171   fixes S :: "'n::euclidean_space set"
```
```  4172   assumes "aff_dim S = int(DIM('n))"
```
```  4173   shows "affine hull S = (UNIV :: ('n::euclidean_space) set)"
```
```  4174 proof -
```
```  4175   have "S \<noteq> {}"
```
```  4176     using assms aff_dim_empty[of S] by auto
```
```  4177   have h0: "S \<subseteq> affine hull S"
```
```  4178     using hull_subset[of S _] by auto
```
```  4179   have h1: "aff_dim (UNIV :: ('n::euclidean_space) set) = aff_dim S"
```
```  4180     using aff_dim_UNIV assms by auto
```
```  4181   then have h2: "aff_dim (affine hull S) \<le> aff_dim (UNIV :: ('n::euclidean_space) set)"
```
```  4182     using aff_dim_le_DIM[of "affine hull S"] assms h0 by auto
```
```  4183   have h3: "aff_dim S \<le> aff_dim (affine hull S)"
```
```  4184     using h0 aff_dim_subset[of S "affine hull S"] assms by auto
```
```  4185   then have h4: "aff_dim (affine hull S) = aff_dim (UNIV :: ('n::euclidean_space) set)"
```
```  4186     using h0 h1 h2 by auto
```
```  4187   then show ?thesis
```
```  4188     using affine_dim_equal[of "affine hull S" "(UNIV :: ('n::euclidean_space) set)"]
```
```  4189       affine_affine_hull[of S] affine_UNIV assms h4 h0 \<open>S \<noteq> {}\<close>
```
```  4190     by auto
```
```  4191 qed
```
```  4192
```
```  4193 lemma disjoint_affine_hull:
```
```  4194   fixes s :: "'n::euclidean_space set"
```
```  4195   assumes "~ affine_dependent s" "t \<subseteq> s" "u \<subseteq> s" "t \<inter> u = {}"
```
```  4196     shows "(affine hull t) \<inter> (affine hull u) = {}"
```
```  4197 proof -
```
```  4198   have "finite s" using assms by (simp add: aff_independent_finite)
```
```  4199   then have "finite t" "finite u" using assms finite_subset by blast+
```
```  4200   { fix y
```
```  4201     assume yt: "y \<in> affine hull t" and yu: "y \<in> affine hull u"
```
```  4202     then obtain a b
```
```  4203            where a1 [simp]: "sum a t = 1" and [simp]: "sum (\<lambda>v. a v *\<^sub>R v) t = y"
```
```  4204              and [simp]: "sum b u = 1" "sum (\<lambda>v. b v *\<^sub>R v) u = y"
```
```  4205       by (auto simp: affine_hull_finite \<open>finite t\<close> \<open>finite u\<close>)
```
```  4206     define c where "c x = (if x \<in> t then a x else if x \<in> u then -(b x) else 0)" for x
```
```  4207     have [simp]: "s \<inter> t = t" "s \<inter> - t \<inter> u = u" using assms by auto
```
```  4208     have "sum c s = 0"
```
```  4209       by (simp add: c_def comm_monoid_add_class.sum.If_cases \<open>finite s\<close> sum_negf)
```
```  4210     moreover have "~ (\<forall>v\<in>s. c v = 0)"
```
```  4211       by (metis (no_types) IntD1 \<open>s \<inter> t = t\<close> a1 c_def sum_not_0 zero_neq_one)
```
```  4212     moreover have "(\<Sum>v\<in>s. c v *\<^sub>R v) = 0"
```
```  4213       by (simp add: c_def if_smult sum_negf
```
```  4214              comm_monoid_add_class.sum.If_cases \<open>finite s\<close>)
```
```  4215     ultimately have False
```
```  4216       using assms \<open>finite s\<close> by (auto simp: affine_dependent_explicit)
```
```  4217   }
```
```  4218   then show ?thesis by blast
```
```  4219 qed
```
```  4220
```
```  4221 lemma aff_dim_convex_hull:
```
```  4222   fixes S :: "'n::euclidean_space set"
```
```  4223   shows "aff_dim (convex hull S) = aff_dim S"
```
```  4224   using aff_dim_affine_hull[of S] convex_hull_subset_affine_hull[of S]
```
```  4225     hull_subset[of S "convex"] aff_dim_subset[of S "convex hull S"]
```
```  4226     aff_dim_subset[of "convex hull S" "affine hull S"]
```
```  4227   by auto
```
```  4228
```
```  4229 lemma aff_dim_cball:
```
```  4230   fixes a :: "'n::euclidean_space"
```
```  4231   assumes "e > 0"
```
```  4232   shows "aff_dim (cball a e) = int (DIM('n))"
```
```  4233 proof -
```
```  4234   have "(\<lambda>x. a + x) ` (cball 0 e) \<subseteq> cball a e"
```
```  4235     unfolding cball_def dist_norm by auto
```
```  4236   then have "aff_dim (cball (0 :: 'n::euclidean_space) e) \<le> aff_dim (cball a e)"
```
```  4237     using aff_dim_translation_eq[of a "cball 0 e"]
```
```  4238           aff_dim_subset[of "(+) a ` cball 0 e" "cball a e"]
```
```  4239     by auto
```
```  4240   moreover have "aff_dim (cball (0 :: 'n::euclidean_space) e) = int (DIM('n))"
```
```  4241     using hull_inc[of "(0 :: 'n::euclidean_space)" "cball 0 e"]
```
```  4242       centre_in_cball[of "(0 :: 'n::euclidean_space)"] assms
```
```  4243     by (simp add: dim_cball[of e] aff_dim_zero[of "cball 0 e"])
```
```  4244   ultimately show ?thesis
```
```  4245     using aff_dim_le_DIM[of "cball a e"] by auto
```
```  4246 qed
```
```  4247
```
```  4248 lemma aff_dim_open:
```
```  4249   fixes S :: "'n::euclidean_space set"
```
```  4250   assumes "open S"
```
```  4251     and "S \<noteq> {}"
```
```  4252   shows "aff_dim S = int (DIM('n))"
```
```  4253 proof -
```
```  4254   obtain x where "x \<in> S"
```
```  4255     using assms by auto
```
```  4256   then obtain e where e: "e > 0" "cball x e \<subseteq> S"
```
```  4257     using open_contains_cball[of S] assms by auto
```
```  4258   then have "aff_dim (cball x e) \<le> aff_dim S"
```
```  4259     using aff_dim_subset by auto
```
```  4260   with e show ?thesis
```
```  4261     using aff_dim_cball[of e x] aff_dim_le_DIM[of S] by auto
```
```  4262 qed
```
```  4263
```
```  4264 lemma low_dim_interior:
```
```  4265   fixes S :: "'n::euclidean_space set"
```
```  4266   assumes "\<not> aff_dim S = int (DIM('n))"
```
```  4267   shows "interior S = {}"
```
```  4268 proof -
```
```  4269   have "aff_dim(interior S) \<le> aff_dim S"
```
```  4270     using interior_subset aff_dim_subset[of "interior S" S] by auto
```
```  4271   then show ?thesis
```
```  4272     using aff_dim_open[of "interior S"] aff_dim_le_DIM[of S] assms by auto
```
```  4273 qed
```
```  4274
```
```  4275 corollary empty_interior_lowdim:
```
```  4276   fixes S :: "'n::euclidean_space set"
```
```  4277   shows "dim S < DIM ('n) \<Longrightarrow> interior S = {}"
```
```  4278 by (metis low_dim_interior affine_hull_UNIV dim_affine_hull less_not_refl dim_UNIV)
```
```  4279
```
```  4280 corollary aff_dim_nonempty_interior:
```
```  4281   fixes S :: "'a::euclidean_space set"
```
```  4282   shows "interior S \<noteq> {} \<Longrightarrow> aff_dim S = DIM('a)"
```
```  4283 by (metis low_dim_interior)
```
```  4284
```
```  4285
```
```  4286 subsection \<open>Caratheodory's theorem\<close>
```
```  4287
```
```  4288 lemma convex_hull_caratheodory_aff_dim:
```
```  4289   fixes p :: "('a::euclidean_space) set"
```
```  4290   shows "convex hull p =
```
```  4291     {y. \<exists>s u. finite s \<and> s \<subseteq> p \<and> card s \<le> aff_dim p + 1 \<and>
```
```  4292       (\<forall>x\<in>s. 0 \<le> u x) \<and> sum u s = 1 \<and> sum (\<lambda>v. u v *\<^sub>R v) s = y}"
```
```  4293   unfolding convex_hull_explicit set_eq_iff mem_Collect_eq
```
```  4294 proof (intro allI iffI)
```
```  4295   fix y
```
```  4296   let ?P = "\<lambda>n. \<exists>s u. finite s \<and> card s = n \<and> s \<subseteq> p \<and> (\<forall>x\<in>s. 0 \<le> u x) \<and>
```
```  4297     sum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = y"
```
```  4298   assume "\<exists>s u. finite s \<and> s \<subseteq> p \<and> (\<forall>x\<in>s. 0 \<le> u x) \<and> sum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = y"
```
```  4299   then obtain N where "?P N" by auto
```
```  4300   then have "\<exists>n\<le>N. (\<forall>k<n. \<not> ?P k) \<and> ?P n"
```
```  4301     apply (rule_tac ex_least_nat_le)
```
```  4302     apply auto
```
```  4303     done
```
```  4304   then obtain n where "?P n" and smallest: "\<forall>k<n. \<not> ?P k"
```
```  4305     by blast
```
```  4306   then obtain s u where obt: "finite s" "card s = n" "s\<subseteq>p" "\<forall>x\<in>s. 0 \<le> u x"
```
```  4307     "sum u s = 1"  "(\<Sum>v\<in>s. u v *\<^sub>R v) = y" by auto
```
```  4308
```
```  4309   have "card s \<le> aff_dim p + 1"
```
```  4310   proof (rule ccontr, simp only: not_le)
```
```  4311     assume "aff_dim p + 1 < card s"
```
```  4312     then have "affine_dependent s"
```
```  4313       using affine_dependent_biggerset[OF obt(1)] independent_card_le_aff_dim not_less obt(3)
```
```  4314       by blast
```
```  4315     then obtain w v where wv: "sum w s = 0" "v\<in>s" "w v \<noteq> 0" "(\<Sum>v\<in>s. w v *\<^sub>R v) = 0"
```
```  4316       using affine_dependent_explicit_finite[OF obt(1)] by auto
```
```  4317     define i where "i = (\<lambda>v. (u v) / (- w v)) ` {v\<in>s. w v < 0}"
```
```  4318     define t where "t = Min i"
```
```  4319     have "\<exists>x\<in>s. w x < 0"
```
```  4320     proof (rule ccontr, simp add: not_less)
```
```  4321       assume as:"\<forall>x\<in>s. 0 \<le> w x"
```
```  4322       then have "sum w (s - {v}) \<ge> 0"
```
```  4323         apply (rule_tac sum_nonneg)
```
```  4324         apply auto
```
```  4325         done
```
```  4326       then have "sum w s > 0"
```
```  4327         unfolding sum.remove[OF obt(1) \<open>v\<in>s\<close>]
```
```  4328         using as[THEN bspec[where x=v]]  \<open>v\<in>s\<close>  \<open>w v \<noteq> 0\<close> by auto
```
```  4329       then show False using wv(1) by auto
```
```  4330     qed
```
```  4331     then have "i \<noteq> {}" unfolding i_def by auto
```
```  4332     then have "t \<ge> 0"
```
```  4333       using Min_ge_iff[of i 0 ] and obt(1)
```
```  4334       unfolding t_def i_def
```
```  4335       using obt(4)[unfolded le_less]
```
```  4336       by (auto simp: divide_le_0_iff)
```
```  4337     have t: "\<forall>v\<in>s. u v + t * w v \<ge> 0"
```
```  4338     proof
```
```  4339       fix v
```
```  4340       assume "v \<in> s"
```
```  4341       then have v: "0 \<le> u v"
```
```  4342         using obt(4)[THEN bspec[where x=v]] by auto
```
```  4343       show "0 \<le> u v + t * w v"
```
```  4344       proof (cases "w v < 0")
```
```  4345         case False
```
```  4346         thus ?thesis using v \<open>t\<ge>0\<close> by auto
```
```  4347       next
```
```  4348         case True
```
```  4349         then have "t \<le> u v / (- w v)"
```
```  4350           using \<open>v\<in>s\<close> unfolding t_def i_def
```
```  4351           apply (rule_tac Min_le)
```
```  4352           using obt(1) apply auto
```
```  4353           done
```
```  4354         then show ?thesis
```
```  4355           unfolding real_0_le_add_iff
```
```  4356           using pos_le_divide_eq[OF True[unfolded neg_0_less_iff_less[symmetric]]]
```
```  4357           by auto
```
```  4358       qed
```
```  4359     qed
```
```  4360     obtain a where "a \<in> s" and "t = (\<lambda>v. (u v) / (- w v)) a" and "w a < 0"
```
```  4361       using Min_in[OF _ \<open>i\<noteq>{}\<close>] and obt(1) unfolding i_def t_def by auto
```
```  4362     then have a: "a \<in> s" "u a + t * w a = 0" by auto
```
```  4363     have *: "\<And>f. sum f (s - {a}) = sum f s - ((f a)::'b::ab_group_add)"
```
```  4364       unfolding sum.remove[OF obt(1) \<open>a\<in>s\<close>] by auto
```
```  4365     have "(\<Sum>v\<in>s. u v + t * w v) = 1"
```
```  4366       unfolding sum.distrib wv(1) sum_distrib_left[symmetric] obt(5) by auto
```
```  4367     moreover have "(\<Sum>v\<in>s. u v *\<^sub>R v + (t * w v) *\<^sub>R v) - (u a *\<^sub>R a + (t * w a) *\<^sub>R a) = y"
```
```  4368       unfolding sum.distrib obt(6) scaleR_scaleR[symmetric] scaleR_right.sum [symmetric] wv(4)
```
```  4369       using a(2) [THEN eq_neg_iff_add_eq_0 [THEN iffD2]] by simp
```
```  4370     ultimately have "?P (n - 1)"
```
```  4371       apply (rule_tac x="(s - {a})" in exI)
```
```  4372       apply (rule_tac x="\<lambda>v. u v + t * w v" in exI)
```
```  4373       using obt(1-3) and t and a
```
```  4374       apply (auto simp add: * scaleR_left_distrib)
```
```  4375       done
```
```  4376     then show False
```
```  4377       using smallest[THEN spec[where x="n - 1"]] by auto
```
```  4378   qed
```
```  4379   then show "\<exists>s u. finite s \<and> s \<subseteq> p \<and> card s \<le> aff_dim p + 1 \<and>
```
```  4380       (\<forall>x\<in>s. 0 \<le> u x) \<and> sum u s = 1 \<and> (\<Sum>v\<in>s. u v *\<^sub>R v) = y"
```
```  4381     using obt by auto
```
```  4382 qed auto
```
```  4383
```
```  4384 lemma caratheodory_aff_dim:
```
```  4385   fixes p :: "('a::euclidean_space) set"
```
```  4386   shows "convex hull p = {x. \<exists>s. finite s \<and> s \<subseteq> p \<and> card s \<le> aff_dim p + 1 \<and> x \<in> convex hull s}"
```
```  4387         (is "?lhs = ?rhs")
```
```  4388 proof
```
```  4389   show "?lhs \<subseteq> ?rhs"
```
```  4390     apply (subst convex_hull_caratheodory_aff_dim)
```
```  4391     apply clarify
```
```  4392     apply (rule_tac x="s" in exI)
```
```  4393     apply (simp add: hull_subset convex_explicit [THEN iffD1, OF convex_convex_hull])
```
```  4394     done
```
```  4395 next
```
```  4396   show "?rhs \<subseteq> ?lhs"
```
```  4397     using hull_mono by blast
```
```  4398 qed
```
```  4399
```
```  4400 lemma convex_hull_caratheodory:
```
```  4401   fixes p :: "('a::euclidean_space) set"
```
```  4402   shows "convex hull p =
```
```  4403             {y. \<exists>s u. finite s \<and> s \<subseteq> p \<and> card s \<le> DIM('a) + 1 \<and>
```
```  4404               (\<forall>x\<in>s. 0 \<le> u x) \<and> sum u s = 1 \<and> sum (\<lambda>v. u v *\<^sub>R v) s = y}"
```
```  4405         (is "?lhs = ?rhs")
```
```  4406 proof (intro set_eqI iffI)
```
```  4407   fix x
```
```  4408   assume "x \<in> ?lhs" then show "x \<in> ?rhs"
```
```  4409     apply (simp only: convex_hull_caratheodory_aff_dim Set.mem_Collect_eq)
```
```  4410     apply (erule ex_forward)+
```
```  4411     using aff_dim_le_DIM [of p]
```
```  4412     apply simp
```
```  4413     done
```
```  4414 next
```
```  4415   fix x
```
```  4416   assume "x \<in> ?rhs" then show "x \<in> ?lhs"
```
```  4417     by (auto simp add: convex_hull_explicit)
```
```  4418 qed
```
```  4419
```
```  4420 theorem%important caratheodory:
```
```  4421   "convex hull p =
```
```  4422     {x::'a::euclidean_space. \<exists>s. finite s \<and> s \<subseteq> p \<and>
```
```  4423       card s \<le> DIM('a) + 1 \<and> x \<in> convex hull s}"
```
```  4424 proof%unimportant safe
```
```  4425   fix x
```
```  4426   assume "x \<in> convex hull p"
```
```  4427   then obtain s u where "finite s" "s \<subseteq> p" "card s \<le> DIM('a) + 1"
```
```  4428     "\<forall>x\<in>s. 0 \<le> u x" "sum u s = 1" "(\<Sum>v\<in>s. u v *\<^sub>R v) = x"
```
```  4429     unfolding convex_hull_caratheodory by auto
```
```  4430   then show "\<exists>s. finite s \<and> s \<subseteq> p \<and> card s \<le> DIM('a) + 1 \<and> x \<in> convex hull s"
```
```  4431     apply (rule_tac x=s in exI)
```
```  4432     using hull_subset[of s convex]
```
```  4433     using convex_convex_hull[simplified convex_explicit, of s,
```
```  4434       THEN spec[where x=s], THEN spec[where x=u]]
```
```  4435     apply auto
```
```  4436     done
```
```  4437 next
```
```  4438   fix x s
```
```  4439   assume  "finite s" "s \<subseteq> p" "card s \<le> DIM('a) + 1" "x \<in> convex hull s"
```
```  4440   then show "x \<in> convex hull p"
```
```  4441     using hull_mono[OF \<open>s\<subseteq>p\<close>] by auto
```
```  4442 qed
```
```  4443
```
```  4444
```
```  4445 subsection \<open>Relative interior of a set\<close>
```
```  4446
```
```  4447 definition%important "rel_interior S =
```
```  4448   {x. \<exists>T. openin (subtopology euclidean (affine hull S)) T \<and> x \<in> T \<and> T \<subseteq> S}"
```
```  4449
```
```  4450 lemma rel_interior_mono:
```
```  4451    "\<lbrakk>S \<subseteq> T; affine hull S = affine hull T\<rbrakk>
```
```  4452    \<Longrightarrow> (rel_interior S) \<subseteq> (rel_interior T)"
```
```  4453   by (auto simp: rel_interior_def)
```
```  4454
```
```  4455 lemma rel_interior_maximal:
```
```  4456    "\<lbrakk>T \<subseteq> S; openin(subtopology euclidean (affine hull S)) T\<rbrakk> \<Longrightarrow> T \<subseteq> (rel_interior S)"
```
```  4457   by (auto simp: rel_interior_def)
```
```  4458
```
```  4459 lemma rel_interior:
```
```  4460   "rel_interior S = {x \<in> S. \<exists>T. open T \<and> x \<in> T \<and> T \<inter> affine hull S \<subseteq> S}"
```
```  4461   unfolding rel_interior_def[of S] openin_open[of "affine hull S"]
```
```  4462   apply auto
```
```  4463 proof -
```
```  4464   fix x T
```
```  4465   assume *: "x \<in> S" "open T" "x \<in> T" "T \<inter> affine hull S \<subseteq> S"
```
```  4466   then have **: "x \<in> T \<inter> affine hull S"
```
```  4467     using hull_inc by auto
```
```  4468   show "\<exists>Tb. (\<exists>Ta. open Ta \<and> Tb = affine hull S \<inter> Ta) \<and> x \<in> Tb \<and> Tb \<subseteq> S"
```
```  4469     apply (rule_tac x = "T \<inter> (affine hull S)" in exI)
```
```  4470     using * **
```
```  4471     apply auto
```
```  4472     done
```
```  4473 qed
```
```  4474
```
```  4475 lemma mem_rel_interior: "x \<in> rel_interior S \<longleftrightarrow> (\<exists>T. open T \<and> x \<in> T \<inter> S \<and> T \<inter> affine hull S \<subseteq> S)"
```
```  4476   by (auto simp add: rel_interior)
```
```  4477
```
```  4478 lemma mem_rel_interior_ball:
```
```  4479   "x \<in> rel_interior S \<longleftrightarrow> x \<in> S \<and> (\<exists>e. e > 0 \<and> ball x e \<inter> affine hull S \<subseteq> S)"
```
```  4480   apply (simp add: rel_interior, safe)
```
```  4481   apply (force simp add: open_contains_ball)
```
```  4482   apply (rule_tac x = "ball x e" in exI)
```
```  4483   apply simp
```
```  4484   done
```
```  4485
```
```  4486 lemma rel_interior_ball:
```
```  4487   "rel_interior S = {x \<in> S. \<exists>e. e > 0 \<and> ball x e \<inter> affine hull S \<subseteq> S}"
```
```  4488   using mem_rel_interior_ball [of _ S] by auto
```
```  4489
```
```  4490 lemma mem_rel_interior_cball:
```
```  4491   "x \<in> rel_interior S \<longleftrightarrow> x \<in> S \<and> (\<exists>e. e > 0 \<and> cball x e \<inter> affine hull S \<subseteq> S)"
```
```  4492   apply (simp add: rel_interior, safe)
```
```  4493   apply (force simp add: open_contains_cball)
```
```  4494   apply (rule_tac x = "ball x e" in exI)
```
```  4495   apply (simp add: subset_trans [OF ball_subset_cball])
```
```  4496   apply auto
```
```  4497   done
```
```  4498
```
```  4499 lemma rel_interior_cball:
```
```  4500   "rel_interior S = {x \<in> S. \<exists>e. e > 0 \<and> cball x e \<inter> affine hull S \<subseteq> S}"
```
```  4501   using mem_rel_interior_cball [of _ S] by auto
```
```  4502
```
```  4503 lemma rel_interior_empty [simp]: "rel_interior {} = {}"
```
```  4504    by (auto simp add: rel_interior_def)
```
```  4505
```
```  4506 lemma affine_hull_sing [simp]: "affine hull {a :: 'n::euclidean_space} = {a}"
```
```  4507   by (metis affine_hull_eq affine_sing)
```
```  4508
```
```  4509 lemma rel_interior_sing [simp]:
```
```  4510     fixes a :: "'n::euclidean_space"  shows "rel_interior {a} = {a}"
```
```  4511   apply (auto simp: rel_interior_ball)
```
```  4512   apply (rule_tac x=1 in exI)
```
```  4513   apply force
```
```  4514   done
```
```  4515
```
```  4516 lemma subset_rel_interior:
```
```  4517   fixes S T :: "'n::euclidean_space set"
```
```  4518   assumes "S \<subseteq> T"
```
```  4519     and "affine hull S = affine hull T"
```
```  4520   shows "rel_interior S \<subseteq> rel_interior T"
```
```  4521   using assms by (auto simp add: rel_interior_def)
```
```  4522
```
```  4523 lemma rel_interior_subset: "rel_interior S \<subseteq> S"
```
```  4524   by (auto simp add: rel_interior_def)
```
```  4525
```
```  4526 lemma rel_interior_subset_closure: "rel_interior S \<subseteq> closure S"
```
```  4527   using rel_interior_subset by (auto simp add: closure_def)
```
```  4528
```
```  4529 lemma interior_subset_rel_interior: "interior S \<subseteq> rel_interior S"
```
```  4530   by (auto simp add: rel_interior interior_def)
```
```  4531
```
```  4532 lemma interior_rel_interior:
```
```  4533   fixes S :: "'n::euclidean_space set"
```
```  4534   assumes "aff_dim S = int(DIM('n))"
```
```  4535   shows "rel_interior S = interior S"
```
```  4536 proof -
```
```  4537   have "affine hull S = UNIV"
```
```  4538     using assms affine_hull_UNIV[of S] by auto
```
```  4539   then show ?thesis
```
```  4540     unfolding rel_interior interior_def by auto
```
```  4541 qed
```
```  4542
```
```  4543 lemma rel_interior_interior:
```
```  4544   fixes S :: "'n::euclidean_space set"
```
```  4545   assumes "affine hull S = UNIV"
```
```  4546   shows "rel_interior S = interior S"
```
```  4547   using assms unfolding rel_interior interior_def by auto
```
```  4548
```
```  4549 lemma rel_interior_open:
```
```  4550   fixes S :: "'n::euclidean_space set"
```
```  4551   assumes "open S"
```
```  4552   shows "rel_interior S = S"
```
```  4553   by (metis assms interior_eq interior_subset_rel_interior rel_interior_subset set_eq_subset)
```
```  4554
```
```  4555 lemma interior_ball [simp]: "interior (ball x e) = ball x e"
```
```  4556   by (simp add: interior_open)
```
```  4557
```
```  4558 lemma interior_rel_interior_gen:
```
```  4559   fixes S :: "'n::euclidean_space set"
```
```  4560   shows "interior S = (if aff_dim S = int(DIM('n)) then rel_interior S else {})"
```
```  4561   by (metis interior_rel_interior low_dim_interior)
```
```  4562
```
```  4563 lemma rel_interior_nonempty_interior:
```
```  4564   fixes S :: "'n::euclidean_space set"
```
```  4565   shows "interior S \<noteq> {} \<Longrightarrow> rel_interior S = interior S"
```
```  4566 by (metis interior_rel_interior_gen)
```
```  4567
```
```  4568 lemma affine_hull_nonempty_interior:
```
```  4569   fixes S :: "'n::euclidean_space set"
```
```  4570   shows "interior S \<noteq> {} \<Longrightarrow> affine hull S = UNIV"
```
```  4571 by (metis affine_hull_UNIV interior_rel_interior_gen)
```
```  4572
```
```  4573 lemma rel_interior_affine_hull [simp]:
```
```  4574   fixes S :: "'n::euclidean_space set"
```
```  4575   shows "rel_interior (affine hull S) = affine hull S"
```
```  4576 proof -
```
```  4577   have *: "rel_interior (affine hull S) \<subseteq> affine hull S"
```
```  4578     using rel_interior_subset by auto
```
```  4579   {
```
```  4580     fix x
```
```  4581     assume x: "x \<in> affine hull S"
```
```  4582     define e :: real where "e = 1"
```
```  4583     then have "e > 0" "ball x e \<inter> affine hull (affine hull S) \<subseteq> affine hull S"
```
```  4584       using hull_hull[of _ S] by auto
```
```  4585     then have "x \<in> rel_interior (affine hull S)"
```
```  4586       using x rel_interior_ball[of "affine hull S"] by auto
```
```  4587   }
```
```  4588   then show ?thesis using * by auto
```
```  4589 qed
```
```  4590
```
```  4591 lemma rel_interior_UNIV [simp]: "rel_interior (UNIV :: ('n::euclidean_space) set) = UNIV"
```
```  4592   by (metis open_UNIV rel_interior_open)
```
```  4593
```
```  4594 lemma rel_interior_convex_shrink:
```
```  4595   fixes S :: "'a::euclidean_space set"
```
```  4596   assumes "convex S"
```
```  4597     and "c \<in> rel_interior S"
```
```  4598     and "x \<in> S"
```
```  4599     and "0 < e"
```
```  4600     and "e \<le> 1"
```
```  4601   shows "x - e *\<^sub>R (x - c) \<in> rel_interior S"
```
```  4602 proof -
```
```  4603   obtain d where "d > 0" and d: "ball c d \<inter> affine hull S \<subseteq> S"
```
```  4604     using assms(2) unfolding  mem_rel_interior_ball by auto
```
```  4605   {
```
```  4606     fix y
```
```  4607     assume as: "dist (x - e *\<^sub>R (x - c)) y < e * d" "y \<in> affine hull S"
```
```  4608     have *: "y = (1 - (1 - e)) *\<^sub>R ((1 / e) *\<^sub>R y - ((1 - e) / e) *\<^sub>R x) + (1 - e) *\<^sub>R x"
```
```  4609       using \<open>e > 0\<close> by (auto simp add: scaleR_left_diff_distrib scaleR_right_diff_distrib)
```
```  4610     have "x \<in> affine hull S"
```
```  4611       using assms hull_subset[of S] by auto
```
```  4612     moreover have "1 / e + - ((1 - e) / e) = 1"
```
```  4613       using \<open>e > 0\<close> left_diff_distrib[of "1" "(1-e)" "1/e"] by auto
```
```  4614     ultimately have **: "(1 / e) *\<^sub>R y - ((1 - e) / e) *\<^sub>R x \<in> affine hull S"
```
```  4615       using as affine_affine_hull[of S] mem_affine[of "affine hull S" y x "(1 / e)" "-((1 - e) / e)"]
```
```  4616       by (simp add: algebra_simps)
```
```  4617     have "dist c ((1 / e) *\<^sub>R y - ((1 - e) / e) *\<^sub>R x) = \<bar>1/e\<bar> * norm (e *\<^sub>R c - y + (1 - e) *\<^sub>R x)"
```
```  4618       unfolding dist_norm norm_scaleR[symmetric]
```
```  4619       apply (rule arg_cong[where f=norm])
```
```  4620       using \<open>e > 0\<close>
```
```  4621       apply (auto simp add: euclidean_eq_iff[where 'a='a] field_simps inner_simps)
```
```  4622       done
```
```  4623     also have "\<dots> = \<bar>1/e\<bar> * norm (x - e *\<^sub>R (x - c) - y)"
```
```  4624       by (auto intro!:arg_cong[where f=norm] simp add: algebra_simps)
```
```  4625     also have "\<dots> < d"
```
```  4626       using as[unfolded dist_norm] and \<open>e > 0\<close>
```
```  4627       by (auto simp add:pos_divide_less_eq[OF \<open>e > 0\<close>] mult.commute)
```
```  4628     finally have "y \<in> S"
```
```  4629       apply (subst *)
```
```  4630       apply (rule assms(1)[unfolded convex_alt,rule_format])
```
```  4631       apply (rule d[unfolded subset_eq,rule_format])
```
```  4632       unfolding mem_ball
```
```  4633       using assms(3-5) **
```
```  4634       apply auto
```
```  4635       done
```
```  4636   }
```
```  4637   then have "ball (x - e *\<^sub>R (x - c)) (e*d) \<inter> affine hull S \<subseteq> S"
```
```  4638     by auto
```
```  4639   moreover have "e * d > 0"
```
```  4640     using \<open>e > 0\<close> \<open>d > 0\<close> by simp
```
```  4641   moreover have c: "c \<in> S"
```
```  4642     using assms rel_interior_subset by auto
```
```  4643   moreover from c have "x - e *\<^sub>R (x - c) \<in> S"
```
```  4644     using convexD_alt[of S x c e]
```
```  4645     apply (simp add: algebra_simps)
```
```  4646     using assms
```
```  4647     apply auto
```
```  4648     done
```
```  4649   ultimately show ?thesis
```
```  4650     using mem_rel_interior_ball[of "x - e *\<^sub>R (x - c)" S] \<open>e > 0\<close> by auto
```
```  4651 qed
```
```  4652
```
```  4653 lemma interior_real_semiline:
```
```  4654   fixes a :: real
```
```  4655   shows "interior {a..} = {a<..}"
```
```  4656 proof -
```
```  4657   {
```
```  4658     fix y
```
```  4659     assume "a < y"
```
```  4660     then have "y \<in> interior {a..}"
```
```  4661       apply (simp add: mem_interior)
```
```  4662       apply (rule_tac x="(y-a)" in exI)
```
```  4663       apply (auto simp add: dist_norm)
```
```  4664       done
```
```  4665   }
```
```  4666   moreover
```
```  4667   {
```
```  4668     fix y
```
```  4669     assume "y \<in> interior {a..}"
```
```  4670     then obtain e where e: "e > 0" "cball y e \<subseteq> {a..}"
```
```  4671       using mem_interior_cball[of y "{a..}"] by auto
```
```  4672     moreover from e have "y - e \<in> cball y e"
```
```  4673       by (auto simp add: cball_def dist_norm)
```
```  4674     ultimately have "a \<le> y - e" by blast
```
```  4675     then have "a < y" using e by auto
```
```  4676   }
```
```  4677   ultimately show ?thesis by auto
```
```  4678 qed
```
```  4679
```
```  4680 lemma continuous_ge_on_Ioo:
```
```  4681   assumes "continuous_on {c..d} g" "\<And>x. x \<in> {c<..<d} \<Longrightarrow> g x \<ge> a" "c < d" "x \<in> {c..d}"
```
```  4682   shows "g (x::real) \<ge> (a::real)"
```
```  4683 proof-
```
```  4684   from assms(3) have "{c..d} = closure {c<..<d}" by (rule closure_greaterThanLessThan[symmetric])
```
```  4685   also from assms(2) have "{c<..<d} \<subseteq> (g -` {a..} \<inter> {c..d})" by auto
```
```  4686   hence "closure {c<..<d} \<subseteq> closure (g -` {a..} \<inter> {c..d})" by (rule closure_mono)
```
```  4687   also from assms(1) have "closed (g -` {a..} \<inter> {c..d})"
```
```  4688     by (auto simp: continuous_on_closed_vimage)
```
```  4689   hence "closure (g -` {a..} \<inter> {c..d}) = g -` {a..} \<inter> {c..d}" by simp
```
```  4690   finally show ?thesis using \<open>x \<in> {c..d}\<close> by auto
```
```  4691 qed
```
```  4692
```
```  4693 lemma interior_real_semiline':
```
```  4694   fixes a :: real
```
```  4695   shows "interior {..a} = {..<a}"
```
```  4696 proof -
```
```  4697   {
```
```  4698     fix y
```
```  4699     assume "a > y"
```
```  4700     then have "y \<in> interior {..a}"
```
```  4701       apply (simp add: mem_interior)
```
```  4702       apply (rule_tac x="(a-y)" in exI)
```
```  4703       apply (auto simp add: dist_norm)
```
```  4704       done
```
```  4705   }
```
```  4706   moreover
```
```  4707   {
```
```  4708     fix y
```
```  4709     assume "y \<in> interior {..a}"
```
```  4710     then obtain e where e: "e > 0" "cball y e \<subseteq> {..a}"
```
```  4711       using mem_interior_cball[of y "{..a}"] by auto
```
```  4712     moreover from e have "y + e \<in> cball y e"
```
```  4713       by (auto simp add: cball_def dist_norm)
```
```  4714     ultimately have "a \<ge> y + e" by auto
```
```  4715     then have "a > y" using e by auto
```
```  4716   }
```
```  4717   ultimately show ?thesis by auto
```
```  4718 qed
```
```  4719
```
```  4720 lemma interior_atLeastAtMost_real [simp]: "interior {a..b} = {a<..<b :: real}"
```
```  4721 proof-
```
```  4722   have "{a..b} = {a..} \<inter> {..b}" by auto
```
```  4723   also have "interior ... = {a<..} \<inter> {..<b}"
```
```  4724     by (simp add: interior_real_semiline interior_real_semiline')
```
```  4725   also have "... = {a<..<b}" by auto
```
```  4726   finally show ?thesis .
```
```  4727 qed
```
```  4728
```
```  4729 lemma interior_atLeastLessThan [simp]:
```
```  4730   fixes a::real shows "interior {a..<b} = {a<..<b}"
```
```  4731   by (metis atLeastLessThan_def greaterThanLessThan_def interior_atLeastAtMost_real interior_Int interior_interior interior_real_semiline)
```
```  4732
```
```  4733 lemma interior_lessThanAtMost [simp]:
```
```  4734   fixes a::real shows "interior {a<..b} = {a<..<b}"
```
```  4735   by (metis atLeastAtMost_def greaterThanAtMost_def interior_atLeastAtMost_real interior_Int
```
```  4736             interior_interior interior_real_semiline)
```
```  4737
```
```  4738 lemma interior_greaterThanLessThan_real [simp]: "interior {a<..<b} = {a<..<b :: real}"
```
```  4739   by (metis interior_atLeastAtMost_real interior_interior)
```
```  4740
```
```  4741 lemma frontier_real_Iic [simp]:
```
```  4742   fixes a :: real
```
```  4743   shows "frontier {..a} = {a}"
```
```  4744   unfolding frontier_def by (auto simp add: interior_real_semiline')
```
```  4745
```
```  4746 lemma rel_interior_real_box [simp]:
```
```  4747   fixes a b :: real
```
```  4748   assumes "a < b"
```
```  4749   shows "rel_interior {a .. b} = {a <..< b}"
```
```  4750 proof -
```
```  4751   have "box a b \<noteq> {}"
```
```  4752     using assms
```
```  4753     unfolding set_eq_iff
```
```  4754     by (auto intro!: exI[of _ "(a + b) / 2"] simp: box_def)
```
```  4755   then show ?thesis
```
```  4756     using interior_rel_interior_gen[of "cbox a b", symmetric]
```
```  4757     by (simp split: if_split_asm del: box_real add: box_real[symmetric] interior_cbox)
```
```  4758 qed
```
```  4759
```
```  4760 lemma rel_interior_real_semiline [simp]:
```
```  4761   fixes a :: real
```
```  4762   shows "rel_interior {a..} = {a<..}"
```
```  4763 proof -
```
```  4764   have *: "{a<..} \<noteq> {}"
```
```  4765     unfolding set_eq_iff by (auto intro!: exI[of _ "a + 1"])
```
```  4766   then show ?thesis using interior_real_semiline interior_rel_interior_gen[of "{a..}"]
```
```  4767     by (auto split: if_split_asm)
```
```  4768 qed
```
```  4769
```
```  4770 subsubsection \<open>Relative open sets\<close>
```
```  4771
```
```  4772 definition%important "rel_open S \<longleftrightarrow> rel_interior S = S"
```
```  4773
```
```  4774 lemma rel_open: "rel_open S \<longleftrightarrow> openin (subtopology euclidean (affine hull S)) S"
```
```  4775   unfolding rel_open_def rel_interior_def
```
```  4776   apply auto
```
```  4777   using openin_subopen[of "subtopology euclidean (affine hull S)" S]
```
```  4778   apply auto
```
```  4779   done
```
```  4780
```
```  4781 lemma openin_rel_interior: "openin (subtopology euclidean (affine hull S)) (rel_interior S)"
```
```  4782   apply (simp add: rel_interior_def)
```
```  4783   apply (subst openin_subopen)
```
```  4784   apply blast
```
```  4785   done
```
```  4786
```
```  4787 lemma openin_set_rel_interior:
```
```  4788    "openin (subtopology euclidean S) (rel_interior S)"
```
```  4789 by (rule openin_subset_trans [OF openin_rel_interior rel_interior_subset hull_subset])
```
```  4790
```
```  4791 lemma affine_rel_open:
```
```  4792   fixes S :: "'n::euclidean_space set"
```
```  4793   assumes "affine S"
```
```  4794   shows "rel_open S"
```
```  4795   unfolding rel_open_def
```
```  4796   using assms rel_interior_affine_hull[of S] affine_hull_eq[of S]
```
```  4797   by metis
```
```  4798
```
```  4799 lemma affine_closed:
```
```  4800   fixes S :: "'n::euclidean_space set"
```
```  4801   assumes "affine S"
```
```  4802   shows "closed S"
```
```  4803 proof -
```
```  4804   {
```
```  4805     assume "S \<noteq> {}"
```
```  4806     then obtain L where L: "subspace L" "affine_parallel S L"
```
```  4807       using assms affine_parallel_subspace[of S] by auto
```
```  4808     then obtain a where a: "S = ((+) a ` L)"
```
```  4809       using affine_parallel_def[of L S] affine_parallel_commut by auto
```
```  4810     from L have "closed L" using closed_subspace by auto
```
```  4811     then have "closed S"
```
```  4812       using closed_translation a by auto
```
```  4813   }
```
```  4814   then show ?thesis by auto
```
```  4815 qed
```
```  4816
```
```  4817 lemma closure_affine_hull:
```
```  4818   fixes S :: "'n::euclidean_space set"
```
```  4819   shows "closure S \<subseteq> affine hull S"
```
```  4820   by (intro closure_minimal hull_subset affine_closed affine_affine_hull)
```
```  4821
```
```  4822 lemma closure_same_affine_hull [simp]:
```
```  4823   fixes S :: "'n::euclidean_space set"
```
```  4824   shows "affine hull (closure S) = affine hull S"
```
```  4825 proof -
```
```  4826   have "affine hull (closure S) \<subseteq> affine hull S"
```
```  4827     using hull_mono[of "closure S" "affine hull S" "affine"]
```
```  4828       closure_affine_hull[of S] hull_hull[of "affine" S]
```
```  4829     by auto
```
```  4830   moreover have "affine hull (closure S) \<supseteq> affine hull S"
```
```  4831     using hull_mono[of "S" "closure S" "affine"] closure_subset by auto
```
```  4832   ultimately show ?thesis by auto
```
```  4833 qed
```
```  4834
```
```  4835 lemma closure_aff_dim [simp]:
```
```  4836   fixes S :: "'n::euclidean_space set"
```
```  4837   shows "aff_dim (closure S) = aff_dim S"
```
```  4838 proof -
```
```  4839   have "aff_dim S \<le> aff_dim (closure S)"
```
```  4840     using aff_dim_subset closure_subset by auto
```
```  4841   moreover have "aff_dim (closure S) \<le> aff_dim (affine hull S)"
```
```  4842     using aff_dim_subset closure_affine_hull by blast
```
```  4843   moreover have "aff_dim (affine hull S) = aff_dim S"
```
```  4844     using aff_dim_affine_hull by auto
```
```  4845   ultimately show ?thesis by auto
```
```  4846 qed
```
```  4847
```
```  4848 lemma rel_interior_closure_convex_shrink:
```
```  4849   fixes S :: "_::euclidean_space set"
```
```  4850   assumes "convex S"
```
```  4851     and "c \<in> rel_interior S"
```
```  4852     and "x \<in> closure S"
```
```  4853     and "e > 0"
```
```  4854     and "e \<le> 1"
```
```  4855   shows "x - e *\<^sub>R (x - c) \<in> rel_interior S"
```
```  4856 proof -
```
```  4857   obtain d where "d > 0" and d: "ball c d \<inter> affine hull S \<subseteq> S"
```
```  4858     using assms(2) unfolding mem_rel_interior_ball by auto
```
```  4859   have "\<exists>y \<in> S. norm (y - x) * (1 - e) < e * d"
```
```  4860   proof (cases "x \<in> S")
```
```  4861     case True
```
```  4862     then show ?thesis using \<open>e > 0\<close> \<open>d > 0\<close>
```
```  4863       apply (rule_tac bexI[where x=x])
```
```  4864       apply (auto)
```
```  4865       done
```
```  4866   next
```
```  4867     case False
```
```  4868     then have x: "x islimpt S"
```
```  4869       using assms(3)[unfolded closure_def] by auto
```
```  4870     show ?thesis
```
```  4871     proof (cases "e = 1")
```
```  4872       case True
```
```  4873       obtain y where "y \<in> S" "y \<noteq> x" "dist y x < 1"
```
```  4874         using x[unfolded islimpt_approachable,THEN spec[where x=1]] by auto
```
```  4875       then show ?thesis
```
```  4876         apply (rule_tac x=y in bexI)
```
```  4877         unfolding True
```
```  4878         using \<open>d > 0\<close>
```
```  4879         apply auto
```
```  4880         done
```
```  4881     next
```
```  4882       case False
```
```  4883       then have "0 < e * d / (1 - e)" and *: "1 - e > 0"
```
```  4884         using \<open>e \<le> 1\<close> \<open>e > 0\<close> \<open>d > 0\<close> by (auto)
```
```  4885       then obtain y where "y \<in> S" "y \<noteq> x" "dist y x < e * d / (1 - e)"
```
```  4886         using x[unfolded islimpt_approachable,THEN spec[where x="e*d / (1 - e)"]] by auto
```
```  4887       then show ?thesis
```
```  4888         apply (rule_tac x=y in bexI)
```
```  4889         unfolding dist_norm
```
```  4890         using pos_less_divide_eq[OF *]
```
```  4891         apply auto
```
```  4892         done
```
```  4893     qed
```
```  4894   qed
```
```  4895   then obtain y where "y \<in> S" and y: "norm (y - x) * (1 - e) < e * d"
```
```  4896     by auto
```
```  4897   define z where "z = c + ((1 - e) / e) *\<^sub>R (x - y)"
```
```  4898   have *: "x - e *\<^sub>R (x - c) = y - e *\<^sub>R (y - z)"
```
```  4899     unfolding z_def using \<open>e > 0\<close>
```
```  4900     by (auto simp add: scaleR_right_diff_distrib scaleR_right_distrib scaleR_left_diff_distrib)
```
```  4901   have zball: "z \<in> ball c d"
```
```  4902     using mem_ball z_def dist_norm[of c]
```
```  4903     using y and assms(4,5)
```
```  4904     by (auto simp add:field_simps norm_minus_commute)
```
```  4905   have "x \<in> affine hull S"
```
```  4906     using closure_affine_hull assms by auto
```
```  4907   moreover have "y \<in> affine hull S"
```
```  4908     using \<open>y \<in> S\<close> hull_subset[of S] by auto
```
```  4909   moreover have "c \<in> affine hull S"
```
```  4910     using assms rel_interior_subset hull_subset[of S] by auto
```
```  4911   ultimately have "z \<in> affine hull S"
```
```  4912     using z_def affine_affine_hull[of S]
```
```  4913       mem_affine_3_minus [of "affine hull S" c x y "(1 - e) / e"]
```
```  4914       assms
```
```  4915     by (auto simp add: field_simps)
```
```  4916   then have "z \<in> S" using d zball by auto
```
```  4917   obtain d1 where "d1 > 0" and d1: "ball z d1 \<le> ball c d"
```
```  4918     using zball open_ball[of c d] openE[of "ball c d" z] by auto
```
```  4919   then have "ball z d1 \<inter> affine hull S \<subseteq> ball c d \<inter> affine hull S"
```
```  4920     by auto
```
```  4921   then have "ball z d1 \<inter> affine hull S \<subseteq> S"
```
```  4922     using d by auto
```
```  4923   then have "z \<in> rel_interior S"
```
```  4924     using mem_rel_interior_ball using \<open>d1 > 0\<close> \<open>z \<in> S\<close> by auto
```
```  4925   then have "y - e *\<^sub>R (y - z) \<in> rel_interior S"
```
```  4926     using rel_interior_convex_shrink[of S z y e] assms \<open>y \<in> S\<close> by auto
```
```  4927   then show ?thesis using * by auto
```
```  4928 qed
```
```  4929
```
```  4930 lemma rel_interior_eq:
```
```  4931    "rel_interior s = s \<longleftrightarrow> openin(subtopology euclidean (affine hull s)) s"
```
```  4932 using rel_open rel_open_def by blast
```
```  4933
```
```  4934 lemma rel_interior_openin:
```
```  4935    "openin(subtopology euclidean (affine hull s)) s \<Longrightarrow> rel_interior s = s"
```
```  4936 by (simp add: rel_interior_eq)
```
```  4937
```
```  4938 lemma rel_interior_affine:
```
```  4939   fixes S :: "'n::euclidean_space set"
```
```  4940   shows  "affine S \<Longrightarrow> rel_interior S = S"
```
```  4941 using affine_rel_open rel_open_def by auto
```
```  4942
```
```  4943 lemma rel_interior_eq_closure:
```
```  4944   fixes S :: "'n::euclidean_space set"
```
```  4945   shows "rel_interior S = closure S \<longleftrightarrow> affine S"
```
```  4946 proof (cases "S = {}")
```
```  4947   case True
```
```  4948  then show ?thesis
```
```  4949     by auto
```
```  4950 next
```
```  4951   case False show ?thesis
```
```  4952   proof
```
```  4953     assume eq: "rel_interior S = closure S"
```
```  4954     have "S = {} \<or> S = affine hull S"
```
```  4955       apply (rule connected_clopen [THEN iffD1, rule_format])
```
```  4956        apply (simp add: affine_imp_convex convex_connected)
```
```  4957       apply (rule conjI)
```
```  4958        apply (metis eq closure_subset openin_rel_interior rel_interior_subset subset_antisym)
```
```  4959       apply (metis closed_subset closure_subset_eq eq hull_subset rel_interior_subset)
```
```  4960       done
```
```  4961     with False have "affine hull S = S"
```
```  4962       by auto
```
```  4963     then show "affine S"
```
```  4964       by (metis affine_hull_eq)
```
```  4965   next
```
```  4966     assume "affine S"
```
```  4967     then show "rel_interior S = closure S"
```
```  4968       by (simp add: rel_interior_affine affine_closed)
```
```  4969   qed
```
```  4970 qed
```
```  4971
```
```  4972
```
```  4973 subsubsection%unimportant\<open>Relative interior preserves under linear transformations\<close>
```
```  4974
```
```  4975 lemma rel_interior_translation_aux:
```
```  4976   fixes a :: "'n::euclidean_space"
```
```  4977   shows "((\<lambda>x. a + x) ` rel_interior S) \<subseteq> rel_interior ((\<lambda>x. a + x) ` S)"
```
```  4978 proof -
```
```  4979   {
```
```  4980     fix x
```
```  4981     assume x: "x \<in> rel_interior S"
```
```  4982     then obtain T where "open T" "x \<in> T \<inter> S" "T \<inter> affine hull S \<subseteq> S"
```
```  4983       using mem_rel_interior[of x S] by auto
```
```  4984     then have "open ((\<lambda>x. a + x) ` T)"
```
```  4985       and "a + x \<in> ((\<lambda>x. a + x) ` T) \<inter> ((\<lambda>x. a + x) ` S)"
```
```  4986       and "((\<lambda>x. a + x) ` T) \<inter> affine hull ((\<lambda>x. a + x) ` S) \<subseteq> (\<lambda>x. a + x) ` S"
```
```  4987       using affine_hull_translation[of a S] open_translation[of T a] x by auto
```
```  4988     then have "a + x \<in> rel_interior ((\<lambda>x. a + x) ` S)"
```
```  4989       using mem_rel_interior[of "a+x" "((\<lambda>x. a + x) ` S)"] by auto
```
```  4990   }
```
```  4991   then show ?thesis by auto
```
```  4992 qed
```
```  4993
```
```  4994 lemma rel_interior_translation:
```
```  4995   fixes a :: "'n::euclidean_space"
```
```  4996   shows "rel_interior ((\<lambda>x. a + x) ` S) = (\<lambda>x. a + x) ` rel_interior S"
```
```  4997 proof -
```
```  4998   have "(\<lambda>x. (-a) + x) ` rel_interior ((\<lambda>x. a + x) ` S) \<subseteq> rel_interior S"
```
```  4999     using rel_interior_translation_aux[of "-a" "(\<lambda>x. a + x) ` S"]
```
```  5000       translation_assoc[of "-a" "a"]
```
```  5001     by auto
```
```  5002   then have "((\<lambda>x. a + x) ` rel_interior S) \<supseteq> rel_interior ((\<lambda>x. a + x) ` S)"
```
```  5003     using translation_inverse_subset[of a "rel_interior ((+) a ` S)" "rel_interior S"]
```
```  5004     by auto
```
```  5005   then show ?thesis
```
```  5006     using rel_interior_translation_aux[of a S] by auto
```
```  5007 qed
```
```  5008
```
```  5009
```
```  5010 lemma affine_hull_linear_image:
```
```  5011   assumes "bounded_linear f"
```
```  5012   shows "f ` (affine hull s) = affine hull f ` s"
```
```  5013   apply rule
```
```  5014   unfolding subset_eq ball_simps
```
```  5015   apply (rule_tac[!] hull_induct, rule hull_inc)
```
```  5016   prefer 3
```
```  5017   apply (erule imageE)
```
```  5018   apply (rule_tac x=xa in image_eqI)
```
```  5019   apply assumption
```
```  5020   apply (rule hull_subset[unfolded subset_eq, rule_format])
```
```  5021   apply assumption
```
```  5022 proof -
```
```  5023   interpret f: bounded_linear f by fact
```
```  5024   show "affine {x. f x \<in> affine hull f ` s}"
```
```  5025     unfolding affine_def
```
```  5026     by (auto simp add: f.scaleR f.add affine_affine_hull[unfolded affine_def, rule_format])
```
```  5027   show "affine {x. x \<in> f ` (affine hull s)}"
```
```  5028     using affine_affine_hull[unfolded affine_def, of s]
```
```  5029     unfolding affine_def by (auto simp add: f.scaleR [symmetric] f.add [symmetric])
```
```  5030 qed auto
```
```  5031
```
```  5032
```
```  5033 lemma rel_interior_injective_on_span_linear_image:
```
```  5034   fixes f :: "'m::euclidean_space \<Rightarrow> 'n::euclidean_space"
```
```  5035     and S :: "'m::euclidean_space set"
```
```  5036   assumes "bounded_linear f"
```
```  5037     and "inj_on f (span S)"
```
```  5038   shows "rel_interior (f ` S) = f ` (rel_interior S)"
```
```  5039 proof -
```
```  5040   {
```
```  5041     fix z
```
```  5042     assume z: "z \<in> rel_interior (f ` S)"
```
```  5043     then have "z \<in> f ` S"
```
```  5044       using rel_interior_subset[of "f ` S"] by auto
```
```  5045     then obtain x where x: "x \<in> S" "f x = z" by auto
```
```  5046     obtain e2 where e2: "e2 > 0" "cball z e2 \<inter> affine hull (f ` S) \<subseteq> (f ` S)"
```
```  5047       using z rel_interior_cball[of "f ` S"] by auto
```
```  5048     obtain K where K: "K > 0" "\<And>x. norm (f x) \<le> norm x * K"
```
```  5049      using assms Real_Vector_Spaces.bounded_linear.pos_bounded[of f] by auto
```
```  5050     define e1 where "e1 = 1 / K"
```
```  5051     then have e1: "e1 > 0" "\<And>x. e1 * norm (f x) \<le> norm x"
```
```  5052       using K pos_le_divide_eq[of e1] by auto
```
```  5053     define e where "e = e1 * e2"
```
```  5054     then have "e > 0" using e1 e2 by auto
```
```  5055     {
```
```  5056       fix y
```
```  5057       assume y: "y \<in> cball x e \<inter> affine hull S"
```
```  5058       then have h1: "f y \<in> affine hull (f ` S)"
```
```  5059         using affine_hull_linear_image[of f S] assms by auto
```
```  5060       from y have "norm (x-y) \<le> e1 * e2"
```
```  5061         using cball_def[of x e] dist_norm[of x y] e_def by auto
```
```  5062       moreover have "f x - f y = f (x - y)"
```
```  5063         using assms linear_diff[of f x y] linear_conv_bounded_linear[of f] by auto
```
```  5064       moreover have "e1 * norm (f (x-y)) \<le> norm (x - y)"
```
```  5065         using e1 by auto
```
```  5066       ultimately have "e1 * norm ((f x)-(f y)) \<le> e1 * e2"
```
```  5067         by auto
```
```  5068       then have "f y \<in> cball z e2"
```
```  5069         using cball_def[of "f x" e2] dist_norm[of "f x" "f y"] e1 x by auto
```
```  5070       then have "f y \<in> f ` S"
```
```  5071         using y e2 h1 by auto
```
```  5072       then have "y \<in> S"
```
```  5073         using assms y hull_subset[of S] affine_hull_subset_span
```
```  5074           inj_on_image_mem_iff [OF \<open>inj_on f (span S)\<close>]
```
```  5075         by (metis Int_iff span_inc subsetCE)
```
```  5076     }
```
```  5077     then have "z \<in> f ` (rel_interior S)"
```
```  5078       using mem_rel_interior_cball[of x S] \<open>e > 0\<close> x by auto
```
```  5079   }
```
```  5080   moreover
```
```  5081   {
```
```  5082     fix x
```
```  5083     assume x: "x \<in> rel_interior S"
```
```  5084     then obtain e2 where e2: "e2 > 0" "cball x e2 \<inter> affine hull S \<subseteq> S"
```
```  5085       using rel_interior_cball[of S] by auto
```
```  5086     have "x \<in> S" using x rel_interior_subset by auto
```
```  5087     then have *: "f x \<in> f ` S" by auto
```
```  5088     have "\<forall>x\<in>span S. f x = 0 \<longrightarrow> x = 0"
```
```  5089       using assms subspace_span linear_conv_bounded_linear[of f]
```
```  5090         linear_injective_on_subspace_0[of f "span S"]
```
```  5091       by auto
```
```  5092     then obtain e1 where e1: "e1 > 0" "\<forall>x \<in> span S. e1 * norm x \<le> norm (f x)"
```
```  5093       using assms injective_imp_isometric[of "span S" f]
```
```  5094         subspace_span[of S] closed_subspace[of "span S"]
```
```  5095       by auto
```
```  5096     define e where "e = e1 * e2"
```
```  5097     hence "e > 0" using e1 e2 by auto
```
```  5098     {
```
```  5099       fix y
```
```  5100       assume y: "y \<in> cball (f x) e \<inter> affine hull (f ` S)"
```
```  5101       then have "y \<in> f ` (affine hull S)"
```
```  5102         using affine_hull_linear_image[of f S] assms by auto
```
```  5103       then obtain xy where xy: "xy \<in> affine hull S" "f xy = y" by auto
```
```  5104       with y have "norm (f x - f xy) \<le> e1 * e2"
```
```  5105         using cball_def[of "f x" e] dist_norm[of "f x" y] e_def by auto
```
```  5106       moreover have "f x - f xy = f (x - xy)"
```
```  5107         using assms linear_diff[of f x xy] linear_conv_bounded_linear[of f] by auto
```
```  5108       moreover have *: "x - xy \<in> span S"
```
```  5109         using subspace_diff[of "span S" x xy] subspace_span \<open>x \<in> S\<close> xy
```
```  5110           affine_hull_subset_span[of S] span_inc
```
```  5111         by auto
```
```  5112       moreover from * have "e1 * norm (x - xy) \<le> norm (f (x - xy))"
```
```  5113         using e1 by auto
```
```  5114       ultimately have "e1 * norm (x - xy) \<le> e1 * e2"
```
```  5115         by auto
```
```  5116       then have "xy \<in> cball x e2"
```
```  5117         using cball_def[of x e2] dist_norm[of x xy] e1 by auto
```
```  5118       then have "y \<in> f ` S"
```
```  5119         using xy e2 by auto
```
```  5120     }
```
```  5121     then have "f x \<in> rel_interior (f ` S)"
```
```  5122       using mem_rel_interior_cball[of "(f x)" "(f ` S)"] * \<open>e > 0\<close> by auto
```
```  5123   }
```
```  5124   ultimately show ?thesis by auto
```
```  5125 qed
```
```  5126
```
```  5127 lemma rel_interior_injective_linear_image:
```
```  5128   fixes f :: "'m::euclidean_space \<Rightarrow> 'n::euclidean_space"
```
```  5129   assumes "bounded_linear f"
```
```  5130     and "inj f"
```
```  5131   shows "rel_interior (f ` S) = f ` (rel_interior S)"
```
```  5132   using assms rel_interior_injective_on_span_linear_image[of f S]
```
```  5133     subset_inj_on[of f "UNIV" "span S"]
```
```  5134   by auto
```
```  5135
```
```  5136
```
```  5137 subsection%unimportant\<open>Some Properties of subset of standard basis\<close>
```
```  5138
```
```  5139 lemma affine_hull_substd_basis:
```
```  5140   assumes "d \<subseteq> Basis"
```
```  5141   shows "affine hull (insert 0 d) = {x::'a::euclidean_space. \<forall>i\<in>Basis. i \<notin> d \<longrightarrow> x\<bullet>i = 0}"
```
```  5142   (is "affine hull (insert 0 ?A) = ?B")
```
```  5143 proof -
```
```  5144   have *: "\<And>A. (+) (0::'a) ` A = A" "\<And>A. (+) (- (0::'a)) ` A = A"
```
```  5145     by auto
```
```  5146   show ?thesis
```
```  5147     unfolding affine_hull_insert_span_gen span_substd_basis[OF assms,symmetric] * ..
```
```  5148 qed
```
```  5149
```
```  5150 lemma affine_hull_convex_hull [simp]: "affine hull (convex hull S) = affine hull S"
```
```  5151   by (metis Int_absorb1 Int_absorb2 convex_hull_subset_affine_hull hull_hull hull_mono hull_subset)
```
```  5152
```
```  5153
```
```  5154 subsection%unimportant \<open>Openness and compactness are preserved by convex hull operation\<close>
```
```  5155
```
```  5156 lemma open_convex_hull[intro]:
```
```  5157   fixes s :: "'a::real_normed_vector set"
```
```  5158   assumes "open s"
```
```  5159   shows "open (convex hull s)"
```
```  5160   unfolding open_contains_cball convex_hull_explicit
```
```  5161   unfolding mem_Collect_eq ball_simps(8)
```
```  5162 proof (rule, rule)
```
```  5163   fix a
```
```  5164   assume "\<exists>sa u. finite sa \<and> sa \<subseteq> s \<and> (\<forall>x\<in>sa. 0 \<le> u x) \<and> sum u sa = 1 \<and> (\<Sum>v\<in>sa. u v *\<^sub>R v) = a"
```
```  5165   then obtain t u where obt: "finite t" "t\<subseteq>s" "\<forall>x\<in>t. 0 \<le> u x" "sum u t = 1" "(\<Sum>v\<in>t. u v *\<^sub>R v) = a"
```
```  5166     by auto
```
```  5167
```
```  5168   from assms[unfolded open_contains_cball] obtain b
```
```  5169     where b: "\<forall>x\<in>s. 0 < b x \<and> cball x (b x) \<subseteq> s"
```
```  5170     using bchoice[of s "\<lambda>x e. e > 0 \<and> cball x e \<subseteq> s"] by auto
```
```  5171   have "b ` t \<noteq> {}"
```
```  5172     using obt by auto
```
```  5173   define i where "i = b ` t"
```
```  5174
```
```  5175   show "\<exists>e > 0.
```
```  5176     cball a e \<subseteq> {y. \<exists>sa u. finite sa \<and> sa \<subseteq> s \<and> (\<forall>x\<in>sa. 0 \<le> u x) \<and> sum u sa = 1 \<and> (\<Sum>v\<in>sa. u v *\<^sub>R v) = y}"
```
```  5177     apply (rule_tac x = "Min i" in exI)
```
```  5178     unfolding subset_eq
```
```  5179     apply rule
```
```  5180     defer
```
```  5181     apply rule
```
```  5182     unfolding mem_Collect_eq
```
```  5183   proof -
```
```  5184     show "0 < Min i"
```
```  5185       unfolding i_def and Min_gr_iff[OF finite_imageI[OF obt(1)] \<open>b ` t\<noteq>{}\<close>]
```
```  5186       using b
```
```  5187       apply simp
```
```  5188       apply rule
```
```  5189       apply (erule_tac x=x in ballE)
```
```  5190       using \<open>t\<subseteq>s\<close>
```
```  5191       apply auto
```
```  5192       done
```
```  5193   next
```
```  5194     fix y
```
```  5195     assume "y \<in> cball a (Min i)"
```
```  5196     then have y: "norm (a - y) \<le> Min i"
```
```  5197       unfolding dist_norm[symmetric] by auto
```
```  5198     {
```
```  5199       fix x
```
```  5200       assume "x \<in> t"
```
```  5201       then have "Min i \<le> b x"
```
```  5202         unfolding i_def
```
```  5203         apply (rule_tac Min_le)
```
```  5204         using obt(1)
```
```  5205         apply auto
```
```  5206         done
```
```  5207       then have "x + (y - a) \<in> cball x (b x)"
```
```  5208         using y unfolding mem_cball dist_norm by auto
```
```  5209       moreover from \<open>x\<in>t\<close> have "x \<in> s"
```
```  5210         using obt(2) by auto
```
```  5211       ultimately have "x + (y - a) \<in> s"
```
```  5212         using y and b[THEN bspec[where x=x]] unfolding subset_eq by fast
```
```  5213     }
```
```  5214     moreover
```
```  5215     have *: "inj_on (\<lambda>v. v + (y - a)) t"
```
```  5216       unfolding inj_on_def by auto
```
```  5217     have "(\<Sum>v\<in>(\<lambda>v. v + (y - a)) ` t. u (v - (y - a))) = 1"
```
```  5218       unfolding sum.reindex[OF *] o_def using obt(4) by auto
```
```  5219     moreover have "(\<Sum>v\<in>(\<lambda>v. v + (y - a)) ` t. u (v - (y - a)) *\<^sub>R v) = y"
```
```  5220       unfolding sum.reindex[OF *] o_def using obt(4,5)
```
```  5221       by (simp add: sum.distrib sum_subtractf scaleR_left.sum[symmetric] scaleR_right_distrib)
```
```  5222     ultimately
```
```  5223     show "\<exists>sa u. finite sa \<and> (\<forall>x\<in>sa. x \<in> s) \<and> (\<forall>x\<in>sa. 0 \<le> u x) \<and> sum u sa = 1 \<and> (\<Sum>v\<in>sa. u v *\<^sub>R v) = y"
```
```  5224       apply (rule_tac x="(\<lambda>v. v + (y - a)) ` t" in exI)
```
```  5225       apply (rule_tac x="\<lambda>v. u (v - (y - a))" in exI)
```
```  5226       using obt(1, 3)
```
```  5227       apply auto
```
```  5228       done
```
```  5229   qed
```
```  5230 qed
```
```  5231
```
```  5232 lemma compact_convex_combinations:
```
```  5233   fixes s t :: "'a::real_normed_vector set"
```
```  5234   assumes "compact s" "compact t"
```
```  5235   shows "compact { (1 - u) *\<^sub>R x + u *\<^sub>R y | x y u. 0 \<le> u \<and> u \<le> 1 \<and> x \<in> s \<and> y \<in> t}"
```
```  5236 proof -
```
```  5237   let ?X = "{0..1} \<times> s \<times> t"
```
```  5238   let ?h = "(\<lambda>z. (1 - fst z) *\<^sub>R fst (snd z) + fst z *\<^sub>R snd (snd z))"
```
```  5239   have *: "{ (1 - u) *\<^sub>R x + u *\<^sub>R y | x y u. 0 \<le> u \<and> u \<le> 1 \<and> x \<in> s \<and> y \<in> t} = ?h ` ?X"
```
```  5240     apply (rule set_eqI)
```
```  5241     unfolding image_iff mem_Collect_eq
```
```  5242     apply rule
```
```  5243     apply auto
```
```  5244     apply (rule_tac x=u in rev_bexI)
```
```  5245     apply simp
```
```  5246     apply (erule rev_bexI)
```
```  5247     apply (erule rev_bexI)
```
```  5248     apply simp
```
```  5249     apply auto
```
```  5250     done
```
```  5251   have "continuous_on ?X (\<lambda>z. (1 - fst z) *\<^sub>R fst (snd z) + fst z *\<^sub>R snd (snd z))"
```
```  5252     unfolding continuous_on by (rule ballI) (intro tendsto_intros)
```
```  5253   then show ?thesis
```
```  5254     unfolding *
```
```  5255     apply (rule compact_continuous_image)
```
```  5256     apply (intro compact_Times compact_Icc assms)
```
```  5257     done
```
```  5258 qed
```
```  5259
```
```  5260 lemma finite_imp_compact_convex_hull:
```
```  5261   fixes s :: "'a::real_normed_vector set"
```
```  5262   assumes "finite s"
```
```  5263   shows "compact (convex hull s)"
```
```  5264 proof (cases "s = {}")
```
```  5265   case True
```
```  5266   then show ?thesis by simp
```
```  5267 next
```
```  5268   case False
```
```  5269   with assms show ?thesis
```
```  5270   proof (induct rule: finite_ne_induct)
```
```  5271     case (singleton x)
```
```  5272     show ?case by simp
```
```  5273   next
```
```  5274     case (insert x A)
```
```  5275     let ?f = "\<lambda>(u, y::'a). u *\<^sub>R x + (1 - u) *\<^sub>R y"
```
```  5276     let ?T = "{0..1::real} \<times> (convex hull A)"
```
```  5277     have "continuous_on ?T ?f"
```
```  5278       unfolding split_def continuous_on by (intro ballI tendsto_intros)
```
```  5279     moreover have "compact ?T"
```
```  5280       by (intro compact_Times compact_Icc insert)
```
```  5281     ultimately have "compact (?f ` ?T)"
```
```  5282       by (rule compact_continuous_image)
```
```  5283     also have "?f ` ?T = convex hull (insert x A)"
```
```  5284       unfolding convex_hull_insert [OF \<open>A \<noteq> {}\<close>]
```
```  5285       apply safe
```
```  5286       apply (rule_tac x=a in exI, simp)
```
```  5287       apply (rule_tac x="1 - a" in exI, simp)
```
```  5288       apply fast
```
```  5289       apply (rule_tac x="(u, b)" in image_eqI, simp_all)
```
```  5290       done
```
```  5291     finally show "compact (convex hull (insert x A))" .
```
```  5292   qed
```
```  5293 qed
```
```  5294
```
```  5295 lemma compact_convex_hull:
```
```  5296   fixes s :: "'a::euclidean_space set"
```
```  5297   assumes "compact s"
```
```  5298   shows "compact (convex hull s)"
```
```  5299 proof (cases "s = {}")
```
```  5300   case True
```
```  5301   then show ?thesis using compact_empty by simp
```
```  5302 next
```
```  5303   case False
```
```  5304   then obtain w where "w \<in> s" by auto
```
```  5305   show ?thesis
```
```  5306     unfolding caratheodory[of s]
```
```  5307   proof (induct ("DIM('a) + 1"))
```
```  5308     case 0
```
```  5309     have *: "{x.\<exists>sa. finite sa \<and> sa \<subseteq> s \<and> card sa \<le> 0 \<and> x \<in> convex hull sa} = {}"
```
```  5310       using compact_empty by auto
```
```  5311     from 0 show ?case unfolding * by simp
```
```  5312   next
```
```  5313     case (Suc n)
```
```  5314     show ?case
```
```  5315     proof (cases "n = 0")
```
```  5316       case True
```
```  5317       have "{x. \<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t} = s"
```
```  5318         unfolding set_eq_iff and mem_Collect_eq
```
```  5319       proof (rule, rule)
```
```  5320         fix x
```
```  5321         assume "\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t"
```
```  5322         then obtain t where t: "finite t" "t \<subseteq> s" "card t \<le> Suc n" "x \<in> convex hull t"
```
```  5323           by auto
```
```  5324         show "x \<in> s"
```
```  5325         proof (cases "card t = 0")
```
```  5326           case True
```
```  5327           then show ?thesis
```
```  5328             using t(4) unfolding card_0_eq[OF t(1)] by simp
```
```  5329         next
```
```  5330           case False
```
```  5331           then have "card t = Suc 0" using t(3) \<open>n=0\<close> by auto
```
```  5332           then obtain a where "t = {a}" unfolding card_Suc_eq by auto
```
```  5333           then show ?thesis using t(2,4) by simp
```
```  5334         qed
```
```  5335       next
```
```  5336         fix x assume "x\<in>s"
```
```  5337         then show "\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t"
```
```  5338           apply (rule_tac x="{x}" in exI)
```
```  5339           unfolding convex_hull_singleton
```
```  5340           apply auto
```
```  5341           done
```
```  5342       qed
```
```  5343       then show ?thesis using assms by simp
```
```  5344     next
```
```  5345       case False
```
```  5346       have "{x. \<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t} =
```
```  5347         {(1 - u) *\<^sub>R x + u *\<^sub>R y | x y u.
```
```  5348           0 \<le> u \<and> u \<le> 1 \<and> x \<in> s \<and> y \<in> {x. \<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> n \<and> x \<in> convex hull t}}"
```
```  5349         unfolding set_eq_iff and mem_Collect_eq
```
```  5350       proof (rule, rule)
```
```  5351         fix x
```
```  5352         assume "\<exists>u v c. x = (1 - c) *\<^sub>R u + c *\<^sub>R v \<and>
```
```  5353           0 \<le> c \<and> c \<le> 1 \<and> u \<in> s \<and> (\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> n \<and> v \<in> convex hull t)"
```
```  5354         then obtain u v c t where obt: "x = (1 - c) *\<^sub>R u + c *\<^sub>R v"
```
```  5355           "0 \<le> c \<and> c \<le> 1" "u \<in> s" "finite t" "t \<subseteq> s" "card t \<le> n"  "v \<in> convex hull t"
```
```  5356           by auto
```
```  5357         moreover have "(1 - c) *\<^sub>R u + c *\<^sub>R v \<in> convex hull insert u t"
```
```  5358           apply (rule convexD_alt)
```
```  5359           using obt(2) and convex_convex_hull and hull_subset[of "insert u t" convex]
```
```  5360           using obt(7) and hull_mono[of t "insert u t"]
```
```  5361           apply auto
```
```  5362           done
```
```  5363         ultimately show "\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t"
```
```  5364           apply (rule_tac x="insert u t" in exI)
```
```  5365           apply (auto simp add: card_insert_if)
```
```  5366           done
```
```  5367       next
```
```  5368         fix x
```
```  5369         assume "\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> Suc n \<and> x \<in> convex hull t"
```
```  5370         then obtain t where t: "finite t" "t \<subseteq> s" "card t \<le> Suc n" "x \<in> convex hull t"
```
```  5371           by auto
```
```  5372         show "\<exists>u v c. x = (1 - c) *\<^sub>R u + c *\<^sub>R v \<and>
```
```  5373           0 \<le> c \<and> c \<le> 1 \<and> u \<in> s \<and> (\<exists>t. finite t \<and> t \<subseteq> s \<and> card t \<le> n \<and> v \<in> convex hull t)"
```
```  5374         proof (cases "card t = Suc n")
```
```  5375           case False
```
```  5376           then have "card t \<le> n" using t(3) by auto
```
```  5377           then show ?thesis
```
```  5378             apply (rule_tac x=w in exI, rule_tac x=x in exI, rule_tac x=1 in exI)
```
```  5379             using \<open>w\<in>s\<close> and t
```
```  5380             apply (auto intro!: exI[where x=t])
```
```  5381             done
```
```  5382         next
```
```  5383           case True
```
```  5384           then obtain a u where au: "t = insert a u" "a\<notin>u"
```
```  5385             apply (drule_tac card_eq_SucD)
```
```  5386             apply auto
```
```  5387             done
```
```  5388           show ?thesis
```
```  5389           proof (cases "u = {}")
```
```  5390             case True
```
```  5391             then have "x = a" using t(4)[unfolded au] by auto
```
```  5392             show ?thesis unfolding \<open>x = a\<close>
```
```  5393               apply (rule_tac x=a in exI)
```
```  5394               apply (rule_tac x=a in exI)
```
```  5395               apply (rule_tac x=1 in exI)
```
```  5396               using t and \<open>n \<noteq> 0\<close>
```
```  5397               unfolding au
```
```  5398               apply (auto intro!: exI[where x="{a}"])
```
```  5399               done
```
```  5400           next
```
```  5401             case False
```
```  5402             obtain ux vx b where obt: "ux\<ge>0" "vx\<ge>0" "ux + vx = 1"
```
```  5403               "b \<in> convex hull u" "x = ux *\<^sub>R a + vx *\<^sub>R b"
```
```  5404               using t(4)[unfolded au convex_hull_insert[OF False]]
```
```  5405               by auto
```
```  5406             have *: "1 - vx = ux" using obt(3) by auto
```
```  5407             show ?thesis
```
```  5408               apply (rule_tac x=a in exI)
```
```  5409               apply (rule_tac x=b in exI)
```
```  5410               apply (rule_tac x=vx in exI)
```
```  5411               using obt and t(1-3)
```
```  5412               unfolding au and * using card_insert_disjoint[OF _ au(2)]
```
```  5413               apply (auto intro!: exI[where x=u])
```
```  5414               done
```
```  5415           qed
```
```  5416         qed
```
```  5417       qed
```
```  5418       then show ?thesis
```
```  5419         using compact_convex_combinations[OF assms Suc] by simp
```
```  5420     qed
```
```  5421   qed
```
```  5422 qed
```
```  5423
```
```  5424
```
```  5425 subsection%unimportant \<open>Extremal points of a simplex are some vertices\<close>
```
```  5426
```
```  5427 lemma dist_increases_online:
```
```  5428   fixes a b d :: "'a::real_inner"
```
```  5429   assumes "d \<noteq> 0"
```
```  5430   shows "dist a (b + d) > dist a b \<or> dist a (b - d) > dist a b"
```
```  5431 proof (cases "inner a d - inner b d > 0")
```
```  5432   case True
```
```  5433   then have "0 < inner d d + (inner a d * 2 - inner b d * 2)"
```
```  5434     apply (rule_tac add_pos_pos)
```
```  5435     using assms
```
```  5436     apply auto
```
```  5437     done
```
```  5438   then show ?thesis
```
```  5439     apply (rule_tac disjI2)
```
```  5440     unfolding dist_norm and norm_eq_sqrt_inner and real_sqrt_less_iff
```
```  5441     apply  (simp add: algebra_simps inner_commute)
```
```  5442     done
```
```  5443 next
```
```  5444   case False
```
```  5445   then have "0 < inner d d + (inner b d * 2 - inner a d * 2)"
```
```  5446     apply (rule_tac add_pos_nonneg)
```
```  5447     using assms
```
```  5448     apply auto
```
```  5449     done
```
```  5450   then show ?thesis
```
```  5451     apply (rule_tac disjI1)
```
```  5452     unfolding dist_norm and norm_eq_sqrt_inner and real_sqrt_less_iff
```
```  5453     apply (simp add: algebra_simps inner_commute)
```
```  5454     done
```
```  5455 qed
```
```  5456
```
```  5457 lemma norm_increases_online:
```
```  5458   fixes d :: "'a::real_inner"
```
```  5459   shows "d \<noteq> 0 \<Longrightarrow> norm (a + d) > norm a \<or> norm(a - d) > norm a"
```
```  5460   using dist_increases_online[of d a 0] unfolding dist_norm by auto
```
```  5461
```
```  5462 lemma simplex_furthest_lt:
```
```  5463   fixes s :: "'a::real_inner set"
```
```  5464   assumes "finite s"
```
```  5465   shows "\<forall>x \<in> convex hull s.  x \<notin> s \<longrightarrow> (\<exists>y \<in> convex hull s. norm (x - a) < norm(y - a))"
```
```  5466   using assms
```
```  5467 proof induct
```
```  5468   fix x s
```
```  5469   assume as: "finite s" "x\<notin>s" "\<forall>x\<in>convex hull s. x \<notin> s \<longrightarrow> (\<exists>y\<in>convex hull s. norm (x - a) < norm (y - a))"
```
```  5470   show "\<forall>xa\<in>convex hull insert x s. xa \<notin> insert x s \<longrightarrow>
```
```  5471     (\<exists>y\<in>convex hull insert x s. norm (xa - a) < norm (y - a))"
```
```  5472   proof (rule, rule, cases "s = {}")
```
```  5473     case False
```
```  5474     fix y
```
```  5475     assume y: "y \<in> convex hull insert x s" "y \<notin> insert x s"
```
```  5476     obtain u v b where obt: "u\<ge>0" "v\<ge>0" "u + v = 1" "b \<in> convex hull s" "y = u *\<^sub>R x + v *\<^sub>R b"
```
```  5477       using y(1)[unfolded convex_hull_insert[OF False]] by auto
```
```  5478     show "\<exists>z\<in>convex hull insert x s. norm (y - a) < norm (z - a)"
```
```  5479     proof (cases "y \<in> convex hull s")
```
```  5480       case True
```
```  5481       then obtain z where "z \<in> convex hull s" "norm (y - a) < norm (z - a)"
```
```  5482         using as(3)[THEN bspec[where x=y]] and y(2) by auto
```
```  5483       then show ?thesis
```
```  5484         apply (rule_tac x=z in bexI)
```
```  5485         unfolding convex_hull_insert[OF False]
```
```  5486         apply auto
```
```  5487         done
```
```  5488     next
```
```  5489       case False
```
```  5490       show ?thesis
```
```  5491         using obt(3)
```
```  5492       proof (cases "u = 0", case_tac[!] "v = 0")
```
```  5493         assume "u = 0" "v \<noteq> 0"
```
```  5494         then have "y = b" using obt by auto
```
```  5495         then show ?thesis using False and obt(4) by auto
```
```  5496       next
```
```  5497         assume "u \<noteq> 0" "v = 0"
```
```  5498         then have "y = x" using obt by auto
```
```  5499         then show ?thesis using y(2) by auto
```
```  5500       next
```
```  5501         assume "u \<noteq> 0" "v \<noteq> 0"
```
```  5502         then obtain w where w: "w>0" "w<u" "w<v"
```
```  5503           using real_lbound_gt_zero[of u v] and obt(1,2) by auto
```
```  5504         have "x \<noteq> b"
```
```  5505         proof
```
```  5506           assume "x = b"
```
```  5507           then have "y = b" unfolding obt(5)
```
```  5508             using obt(3) by (auto simp add: scaleR_left_distrib[symmetric])
```
```  5509           then show False using obt(4) and False by simp
```
```  5510         qed
```
```  5511         then have *: "w *\<^sub>R (x - b) \<noteq> 0" using w(1) by auto
```
```  5512         show ?thesis
```
```  5513           using dist_increases_online[OF *, of a y]
```
```  5514         proof (elim disjE)
```
```  5515           assume "dist a y < dist a (y + w *\<^sub>R (x - b))"
```
```  5516           then have "norm (y - a) < norm ((u + w) *\<^sub>R x + (v - w) *\<^sub>R b - a)"
```
```  5517             unfolding dist_commute[of a]
```
```  5518             unfolding dist_norm obt(5)
```
```  5519             by (simp add: algebra_simps)
```
```  5520           moreover have "(u + w) *\<^sub>R x + (v - w) *\<^sub>R b \<in> convex hull insert x s"
```
```  5521             unfolding convex_hull_insert[OF \<open>s\<noteq>{}\<close>] and mem_Collect_eq
```
```  5522             apply (rule_tac x="u + w" in exI)
```
```  5523             apply rule
```
```  5524             defer
```
```  5525             apply (rule_tac x="v - w" in exI)
```
```  5526             using \<open>u \<ge> 0\<close> and w and obt(3,4)
```
```  5527             apply auto
```
```  5528             done
```
```  5529           ultimately show ?thesis by auto
```
```  5530         next
```
```  5531           assume "dist a y < dist a (y - w *\<^sub>R (x - b))"
```
```  5532           then have "norm (y - a) < norm ((u - w) *\<^sub>R x + (v + w) *\<^sub>R b - a)"
```
```  5533             unfolding dist_commute[of a]
```
```  5534             unfolding dist_norm obt(5)
```
```  5535             by (simp add: algebra_simps)
```
```  5536           moreover have "(u - w) *\<^sub>R x + (v + w) *\<^sub>R b \<in> convex hull insert x s"
```
```  5537             unfolding convex_hull_insert[OF \<open>s\<noteq>{}\<close>] and mem_Collect_eq
```
```  5538             apply (rule_tac x="u - w" in exI)
```
```  5539             apply rule
```
```  5540             defer
```
```  5541             apply (rule_tac x="v + w" in exI)
```
```  5542             using \<open>u \<ge> 0\<close> and w and obt(3,4)
```
```  5543             apply auto
```
```  5544             done
```
```  5545           ultimately show ?thesis by auto
```
```  5546         qed
```
```  5547       qed auto
```
```  5548     qed
```
```  5549   qed auto
```
```  5550 qed (auto simp add: assms)
```
```  5551
```
```  5552 lemma simplex_furthest_le:
```
```  5553   fixes s :: "'a::real_inner set"
```
```  5554   assumes "finite s"
```
```  5555     and "s \<noteq> {}"
```
```  5556   shows "\<exists>y\<in>s. \<forall>x\<in> convex hull s. norm (x - a) \<le> norm (y - a)"
```
```  5557 proof -
```
```  5558   have "convex hull s \<noteq> {}"
```
```  5559     using hull_subset[of s convex] and assms(2) by auto
```
```  5560   then obtain x where x: "x \<in> convex hull s" "\<forall>y\<in>convex hull s. norm (y - a) \<le> norm (x - a)"
```
```  5561     using distance_attains_sup[OF finite_imp_compact_convex_hull[OF assms(1)], of a]
```
```  5562     unfolding dist_commute[of a]
```
```  5563     unfolding dist_norm
```
```  5564     by auto
```
```  5565   show ?thesis
```
```  5566   proof (cases "x \<in> s")
```
```  5567     case False
```
```  5568     then obtain y where "y \<in> convex hull s" "norm (x - a) < norm (y - a)"
```
```  5569       using simplex_furthest_lt[OF assms(1), THEN bspec[where x=x]] and x(1)
```
```  5570       by auto
```
```  5571     then show ?thesis
```
```  5572       using x(2)[THEN bspec[where x=y]] by auto
```
```  5573   next
```
```  5574     case True
```
```  5575     with x show ?thesis by auto
```
```  5576   qed
```
```  5577 qed
```
```  5578
```
```  5579 lemma simplex_furthest_le_exists:
```
```  5580   fixes s :: "('a::real_inner) set"
```
```  5581   shows "finite s \<Longrightarrow> \<forall>x\<in>(convex hull s). \<exists>y\<in>s. norm (x - a) \<le> norm (y - a)"
```
```  5582   using simplex_furthest_le[of s] by (cases "s = {}") auto
```
```  5583
```
```  5584 lemma simplex_extremal_le:
```
```  5585   fixes s :: "'a::real_inner set"
```
```  5586   assumes "finite s"
```
```  5587     and "s \<noteq> {}"
```
```  5588   shows "\<exists>u\<in>s. \<exists>v\<in>s. \<forall>x\<in>convex hull s. \<forall>y \<in> convex hull s. norm (x - y) \<le> norm (u - v)"
```
```  5589 proof -
```
```  5590   have "convex hull s \<noteq> {}"
```
```  5591     using hull_subset[of s convex] and assms(2) by auto
```
```  5592   then obtain u v where obt: "u \<in> convex hull s" "v \<in> convex hull s"
```
```  5593     "\<forall>x\<in>convex hull s. \<forall>y\<in>convex hull s. norm (x - y) \<le> norm (u - v)"
```
```  5594     using compact_sup_maxdistance[OF finite_imp_compact_convex_hull[OF assms(1)]]
```
```  5595     by (auto simp: dist_norm)
```
```  5596   then show ?thesis
```
```  5597   proof (cases "u\<notin>s \<or> v\<notin>s", elim disjE)
```
```  5598     assume "u \<notin> s"
```
```  5599     then obtain y where "y \<in> convex hull s" "norm (u - v) < norm (y - v)"
```
```  5600       using simplex_furthest_lt[OF assms(1), THEN bspec[where x=u]] and obt(1)
```
```  5601       by auto
```
```  5602     then show ?thesis
```
```  5603       using obt(3)[THEN bspec[where x=y], THEN bspec[where x=v]] and obt(2)
```
```  5604       by auto
```
```  5605   next
```
```  5606     assume "v \<notin> s"
```
```  5607     then obtain y where "y \<in> convex hull s" "norm (v - u) < norm (y - u)"
```
```  5608       using simplex_furthest_lt[OF assms(1), THEN bspec[where x=v]] and obt(2)
```
```  5609       by auto
```
```  5610     then show ?thesis
```
```  5611       using obt(3)[THEN bspec[where x=u], THEN bspec[where x=y]] and obt(1)
```
```  5612       by (auto simp add: norm_minus_commute)
```
```  5613   qed auto
```
```  5614 qed
```
```  5615
```
```  5616 lemma simplex_extremal_le_exists:
```
```  5617   fixes s :: "'a::real_inner set"
```
```  5618   shows "finite s \<Longrightarrow> x \<in> convex hull s \<Longrightarrow> y \<in> convex hull s \<Longrightarrow>
```
```  5619     \<exists>u\<in>s. \<exists>v\<in>s. norm (x - y) \<le> norm (u - v)"
```
```  5620   using convex_hull_empty simplex_extremal_le[of s]
```
```  5621   by(cases "s = {}") auto
```
```  5622
```
```  5623
```
```  5624 subsection \<open>Closest point of a convex set is unique, with a continuous projection\<close>
```
```  5625
```
```  5626 definition%important closest_point :: "'a::{real_inner,heine_borel} set \<Rightarrow> 'a \<Rightarrow> 'a"
```
```  5627   where "closest_point s a = (SOME x. x \<in> s \<and> (\<forall>y\<in>s. dist a x \<le> dist a y))"
```
```  5628
```
```  5629 lemma closest_point_exists:
```
```  5630   assumes "closed s"
```
```  5631     and "s \<noteq> {}"
```
```  5632   shows "closest_point s a \<in> s"
```
```  5633     and "\<forall>y\<in>s. dist a (closest_point s a) \<le> dist a y"
```
```  5634   unfolding closest_point_def
```
```  5635   apply(rule_tac[!] someI2_ex)
```
```  5636   apply (auto intro: distance_attains_inf[OF assms(1,2), of a])
```
```  5637   done
```
```  5638
```
```  5639 lemma closest_point_in_set: "closed s \<Longrightarrow> s \<noteq> {} \<Longrightarrow> closest_point s a \<in> s"
```
```  5640   by (meson closest_point_exists)
```
```  5641
```
```  5642 lemma closest_point_le: "closed s \<Longrightarrow> x \<in> s \<Longrightarrow> dist a (closest_point s a) \<le> dist a x"
```
```  5643   using closest_point_exists[of s] by auto
```
```  5644
```
```  5645 lemma closest_point_self:
```
```  5646   assumes "x \<in> s"
```
```  5647   shows "closest_point s x = x"
```
```  5648   unfolding closest_point_def
```
```  5649   apply (rule some1_equality, rule ex1I[of _ x])
```
```  5650   using assms
```
```  5651   apply auto
```
```  5652   done
```
```  5653
```
```  5654 lemma closest_point_refl: "closed s \<Longrightarrow> s \<noteq> {} \<Longrightarrow> closest_point s x = x \<longleftrightarrow> x \<in> s"
```
```  5655   using closest_point_in_set[of s x] closest_point_self[of x s]
```
```  5656   by auto
```
```  5657
```
```  5658 lemma closer_points_lemma:
```
```  5659   assumes "inner y z > 0"
```
```  5660   shows "\<exists>u>0. \<forall>v>0. v \<le> u \<longrightarrow> norm(v *\<^sub>R z - y) < norm y"
```
```  5661 proof -
```
```  5662   have z: "inner z z > 0"
```
```  5663     unfolding inner_gt_zero_iff using assms by auto
```
```  5664   then show ?thesis
```
```  5665     using assms
```
```  5666     apply (rule_tac x = "inner y z / inner z z" in exI)
```
```  5667     apply rule
```
```  5668     defer
```
```  5669   proof rule+
```
```  5670     fix v
```
```  5671     assume "0 < v" and "v \<le> inner y z / inner z z"
```
```  5672     then show "norm (v *\<^sub>R z - y) < norm y"
```
```  5673       unfolding norm_lt using z and assms
```
```  5674       by (simp add: field_simps inner_diff inner_commute mult_strict_left_mono[OF _ \<open>0<v\<close>])
```
```  5675   qed auto
```
```  5676 qed
```
```  5677
```
```  5678 lemma closer_point_lemma:
```
```  5679   assumes "inner (y - x) (z - x) > 0"
```
```  5680   shows "\<exists>u>0. u \<le> 1 \<and> dist (x + u *\<^sub>R (z - x)) y < dist x y"
```
```  5681 proof -
```
```  5682   obtain u where "u > 0"
```
```  5683     and u: "\<forall>v>0. v \<le> u \<longrightarrow> norm (v *\<^sub>R (z - x) - (y - x)) < norm (y - x)"
```
```  5684     using closer_points_lemma[OF assms] by auto
```
```  5685   show ?thesis
```
```  5686     apply (rule_tac x="min u 1" in exI)
```
```  5687     using u[THEN spec[where x="min u 1"]] and \<open>u > 0\<close>
```
```  5688     unfolding dist_norm by (auto simp add: norm_minus_commute field_simps)
```
```  5689 qed
```
```  5690
```
```  5691 lemma any_closest_point_dot:
```
```  5692   assumes "convex s" "closed s" "x \<in> s" "y \<in> s" "\<forall>z\<in>s. dist a x \<le> dist a z"
```
```  5693   shows "inner (a - x) (y - x) \<le> 0"
```
```  5694 proof (rule ccontr)
```
```  5695   assume "\<not> ?thesis"
```
```  5696   then obtain u where u: "u>0" "u\<le>1" "dist (x + u *\<^sub>R (y - x)) a < dist x a"
```
```  5697     using closer_point_lemma[of a x y] by auto
```
```  5698   let ?z = "(1 - u) *\<^sub>R x + u *\<^sub>R y"
```
```  5699   have "?z \<in> s"
```
```  5700     using convexD_alt[OF assms(1,3,4), of u] using u by auto
```
```  5701   then show False
```
```  5702     using assms(5)[THEN bspec[where x="?z"]] and u(3)
```
```  5703     by (auto simp add: dist_commute algebra_simps)
```
```  5704 qed
```
```  5705
```
```  5706 lemma any_closest_point_unique:
```
```  5707   fixes x :: "'a::real_inner"
```
```  5708   assumes "convex s" "closed s" "x \<in> s" "y \<in> s"
```
```  5709     "\<forall>z\<in>s. dist a x \<le> dist a z" "\<forall>z\<in>s. dist a y \<le> dist a z"
```
```  5710   shows "x = y"
```
```  5711   using any_closest_point_dot[OF assms(1-4,5)] and any_closest_point_dot[OF assms(1-2,4,3,6)]
```
```  5712   unfolding norm_pths(1) and norm_le_square
```
```  5713   by (auto simp add: algebra_simps)
```
```  5714
```
```  5715 lemma closest_point_unique:
```
```  5716   assumes "convex s" "closed s" "x \<in> s" "\<forall>z\<in>s. dist a x \<le> dist a z"
```
```  5717   shows "x = closest_point s a"
```
```  5718   using any_closest_point_unique[OF assms(1-3) _ assms(4), of "closest_point s a"]
```
```  5719   using closest_point_exists[OF assms(2)] and assms(3) by auto
```
```  5720
```
```  5721 lemma closest_point_dot:
```
```  5722   assumes "convex s" "closed s" "x \<in> s"
```
```  5723   shows "inner (a - closest_point s a) (x - closest_point s a) \<le> 0"
```
```  5724   apply (rule any_closest_point_dot[OF assms(1,2) _ assms(3)])
```
```  5725   using closest_point_exists[OF assms(2)] and assms(3)
```
```  5726   apply auto
```
```  5727   done
```
```  5728
```
```  5729 lemma closest_point_lt:
```
```  5730   assumes "convex s" "closed s" "x \<in> s" "x \<noteq> closest_point s a"
```
```  5731   shows "dist a (closest_point s a) < dist a x"
```
```  5732   apply (rule ccontr)
```
```  5733   apply (rule_tac notE[OF assms(4)])
```
```  5734   apply (rule closest_point_unique[OF assms(1-3), of a])
```
```  5735   using closest_point_le[OF assms(2), of _ a]
```
```  5736   apply fastforce
```
```  5737   done
```
```  5738
```
```  5739 lemma closest_point_lipschitz:
```
```  5740   assumes "convex s"
```
```  5741     and "closed s" "s \<noteq> {}"
```
```  5742   shows "dist (closest_point s x) (closest_point s y) \<le> dist x y"
```
```  5743 proof -
```
```  5744   have "inner (x - closest_point s x) (closest_point s y - closest_point s x) \<le> 0"
```
```  5745     and "inner (y - closest_point s y) (closest_point s x - closest_point s y) \<le> 0"
```
```  5746     apply (rule_tac[!] any_closest_point_dot[OF assms(1-2)])
```
```  5747     using closest_point_exists[OF assms(2-3)]
```
```  5748     apply auto
```
```  5749     done
```
```  5750   then show ?thesis unfolding dist_norm and norm_le
```
```  5751     using inner_ge_zero[of "(x - closest_point s x) - (y - closest_point s y)"]
```
```  5752     by (simp add: inner_add inner_diff inner_commute)
```
```  5753 qed
```
```  5754
```
```  5755 lemma continuous_at_closest_point:
```
```  5756   assumes "convex s"
```
```  5757     and "closed s"
```
```  5758     and "s \<noteq> {}"
```
```  5759   shows "continuous (at x) (closest_point s)"
```
```  5760   unfolding continuous_at_eps_delta
```
```  5761   using le_less_trans[OF closest_point_lipschitz[OF assms]] by auto
```
```  5762
```
```  5763 lemma continuous_on_closest_point:
```
```  5764   assumes "convex s"
```
```  5765     and "closed s"
```
```  5766     and "s \<noteq> {}"
```
```  5767   shows "continuous_on t (closest_point s)"
```
```  5768   by (metis continuous_at_imp_continuous_on continuous_at_closest_point[OF assms])
```
```  5769
```
```  5770 proposition closest_point_in_rel_interior:
```
```  5771   assumes "closed S" "S \<noteq> {}" and x: "x \<in> affine hull S"
```
```  5772     shows "closest_point S x \<in> rel_interior S \<longleftrightarrow> x \<in> rel_interior S"
```
```  5773 proof (cases "x \<in> S")
```
```  5774   case True
```
```  5775   then show ?thesis
```
```  5776     by (simp add: closest_point_self)
```
```  5777 next
```
```  5778   case False
```
```  5779   then have "False" if asm: "closest_point S x \<in> rel_interior S"
```
```  5780   proof -
```
```  5781     obtain e where "e > 0" and clox: "closest_point S x \<in> S"
```
```  5782                and e: "cball (closest_point S x) e \<inter> affine hull S \<subseteq> S"
```
```  5783       using asm mem_rel_interior_cball by blast
```
```  5784     then have clo_notx: "closest_point S x \<noteq> x"
```
```  5785       using \<open>x \<notin> S\<close> by auto
```
```  5786     define y where "y \<equiv> closest_point S x -
```
```  5787                         (min 1 (e / norm(closest_point S x - x))) *\<^sub>R (closest_point S x - x)"
```
```  5788     have "x - y = (1 - min 1 (e / norm (closest_point S x - x))) *\<^sub>R (x - closest_point S x)"
```
```  5789       by (simp add: y_def algebra_simps)
```
```  5790     then have "norm (x - y) = abs ((1 - min 1 (e / norm (closest_point S x - x)))) * norm(x - closest_point S x)"
```
```  5791       by simp
```
```  5792     also have "... < norm(x - closest_point S x)"
```
```  5793       using clo_notx \<open>e > 0\<close>
```
```  5794       by (auto simp: mult_less_cancel_right2 divide_simps)
```
```  5795     finally have no_less: "norm (x - y) < norm (x - closest_point S x)" .
```
```  5796     have "y \<in> affine hull S"
```
```  5797       unfolding y_def
```
```  5798       by (meson affine_affine_hull clox hull_subset mem_affine_3_minus2 subsetD x)
```
```  5799     moreover have "dist (closest_point S x) y \<le> e"
```
```  5800       using \<open>e > 0\<close> by (auto simp: y_def min_mult_distrib_right)
```
```  5801     ultimately have "y \<in> S"
```
```  5802       using subsetD [OF e] by simp
```
```  5803     then have "dist x (closest_point S x) \<le> dist x y"
```
```  5804       by (simp add: closest_point_le \<open>closed S\<close>)
```
```  5805     with no_less show False
```
```  5806       by (simp add: dist_norm)
```
```  5807   qed
```
```  5808   moreover have "x \<notin> rel_interior S"
```
```  5809     using rel_interior_subset False by blast
```
```  5810   ultimately show ?thesis by blast
```
```  5811 qed
```
```  5812
```
```  5813
```
```  5814 subsubsection%unimportant \<open>Various point-to-set separating/supporting hyperplane theorems\<close>
```
```  5815
```
```  5816 lemma supporting_hyperplane_closed_point:
```
```  5817   fixes z :: "'a::{real_inner,heine_borel}"
```
```  5818   assumes "convex s"
```
```  5819     and "closed s"
```
```  5820     and "s \<noteq> {}"
```
```  5821     and "z \<notin> s"
```
```  5822   shows "\<exists>a b. \<exists>y\<in>s. inner a z < b \<and> inner a y = b \<and> (\<forall>x\<in>s. inner a x \<ge> b)"
```
```  5823 proof -
```
```  5824   obtain y where "y \<in> s" and y: "\<forall>x\<in>s. dist z y \<le> dist z x"
```
```  5825     by (metis distance_attains_inf[OF assms(2-3)])
```
```  5826   show ?thesis
```
```  5827     apply (rule_tac x="y - z" in exI)
```
```  5828     apply (rule_tac x="inner (y - z) y" in exI)
```
```  5829     apply (rule_tac x=y in bexI)
```
```  5830     apply rule
```
```  5831     defer
```
```  5832     apply rule
```
```  5833     defer
```
```  5834     apply rule
```
```  5835     apply (rule ccontr)
```
```  5836     using \<open>y \<in> s\<close>
```
```  5837   proof -
```
```  5838     show "inner (y - z) z < inner (y - z) y"
```
```  5839       apply (subst diff_gt_0_iff_gt [symmetric])
```
```  5840       unfolding inner_diff_right[symmetric] and inner_gt_zero_iff
```
```  5841       using \<open>y\<in>s\<close> \<open>z\<notin>s\<close>
```
```  5842       apply auto
```
```  5843       done
```
```  5844   next
```
```  5845     fix x
```
```  5846     assume "x \<in> s"
```
```  5847     have *: "\<forall>u. 0 \<le> u \<and> u \<le> 1 \<longrightarrow> dist z y \<le> dist z ((1 - u) *\<^sub>R y + u *\<^sub>R x)"
```
```  5848       using assms(1)[unfolded convex_alt] and y and \<open>x\<in>s\<close> and \<open>y\<in>s\<close> by auto
```
```  5849     assume "\<not> inner (y - z) y \<le> inner (y - z) x"
```
```  5850     then obtain v where "v > 0" "v \<le> 1" "dist (y + v *\<^sub>R (x - y)) z < dist y z"
```
```  5851       using closer_point_lemma[of z y x] by (auto simp add: inner_diff)
```
```  5852     then show False
```
```  5853       using *[THEN spec[where x=v]] by (auto simp add: dist_commute algebra_simps)
```
```  5854   qed auto
```
```  5855 qed
```
```  5856
```
```  5857 lemma separating_hyperplane_closed_point:
```
```  5858   fixes z :: "'a::{real_inner,heine_borel}"
```
```  5859   assumes "convex s"
```
```  5860     and "closed s"
```
```  5861     and "z \<notin> s"
```
```  5862   shows "\<exists>a b. inner a z < b \<and> (\<forall>x\<in>s. inner a x > b)"
```
```  5863 proof (cases "s = {}")
```
```  5864   case True
```
```  5865   then show ?thesis
```
```  5866     apply (rule_tac x="-z" in exI)
```
```  5867     apply (rule_tac x=1 in exI)
```
```  5868     using less_le_trans[OF _ inner_ge_zero[of z]]
```
```  5869     apply auto
```
```  5870     done
```
```  5871 next
```
```  5872   case False
```
```  5873   obtain y where "y \<in> s" and y: "\<forall>x\<in>s. dist z y \<le> dist z x"
```
```  5874     by (metis distance_attains_inf[OF assms(2) False])
```
```  5875   show ?thesis
```
```  5876     apply (rule_tac x="y - z" in exI)
```
```  5877     apply (rule_tac x="inner (y - z) z + (norm (y - z))\<^sup>2 / 2" in exI)
```
```  5878     apply rule
```
```  5879     defer
```
```  5880     apply rule
```
```  5881   proof -
```
```  5882     fix x
```
```  5883     assume "x \<in> s"
```
```  5884     have "\<not> 0 < inner (z - y) (x - y)"
```
```  5885       apply (rule notI)
```
```  5886       apply (drule closer_point_lemma)
```
```  5887     proof -
```
```  5888       assume "\<exists>u>0. u \<le> 1 \<and> dist (y + u *\<^sub>R (x - y)) z < dist y z"
```
```  5889       then obtain u where "u > 0" "u \<le> 1" "dist (y + u *\<^sub>R (x - y)) z < dist y z"
```
```  5890         by auto
```
```  5891       then show False using y[THEN bspec[where x="y + u *\<^sub>R (x - y)"]]
```
```  5892         using assms(1)[unfolded convex_alt, THEN bspec[where x=y]]
```
```  5893         using \<open>x\<in>s\<close> \<open>y\<in>s\<close> by (auto simp add: dist_commute algebra_simps)
```
```  5894     qed
```
```  5895     moreover have "0 < (norm (y - z))\<^sup>2"
```
```  5896       using \<open>y\<in>s\<close> \<open>z\<notin>s\<close> by auto
```
```  5897     then have "0 < inner (y - z) (y - z)"
```
```  5898       unfolding power2_norm_eq_inner by simp
```
```  5899     ultimately show "inner (y - z) z + (norm (y - z))\<^sup>2 / 2 < inner (y - z) x"
```
```  5900       unfolding power2_norm_eq_inner and not_less
```
```  5901       by (auto simp add: field_simps inner_commute inner_diff)
```
```  5902   qed (insert \<open>y\<in>s\<close> \<open>z\<notin>s\<close>, auto)
```
```  5903 qed
```
```  5904
```
```  5905 lemma separating_hyperplane_closed_0:
```
```  5906   assumes "convex (s::('a::euclidean_space) set)"
```
```  5907     and "closed s"
```
```  5908     and "0 \<notin> s"
```
```  5909   shows "\<exists>a b. a \<noteq> 0 \<and> 0 < b \<and> (\<forall>x\<in>s. inner a x > b)"
```
```  5910 proof (cases "s = {}")
```
```  5911   case True
```
```  5912   have "norm ((SOME i. i\<in>Basis)::'a) = 1" "(SOME i. i\<in>Basis) \<noteq> (0::'a)"
```
```  5913     defer
```
```  5914     apply (subst norm_le_zero_iff[symmetric])
```
```  5915     apply (auto simp: SOME_Basis)
```
```  5916     done
```
```  5917   then show ?thesis
```
```  5918     apply (rule_tac x="SOME i. i\<in>Basis" in exI)
```
```  5919     apply (rule_tac x=1 in exI)
```
```  5920     using True using DIM_positive[where 'a='a]
```
```  5921     apply auto
```
```  5922     done
```
```  5923 next
```
```  5924   case False
```
```  5925   then show ?thesis
```
```  5926     using False using separating_hyperplane_closed_point[OF assms]
```
```  5927     apply (elim exE)
```
```  5928     unfolding inner_zero_right
```
```  5929     apply (rule_tac x=a in exI)
```
```  5930     apply (rule_tac x=b in exI)
```
```  5931     apply auto
```
```  5932     done
```
```  5933 qed
```
```  5934
```
```  5935
```
```  5936 subsubsection%unimportant \<open>Now set-to-set for closed/compact sets\<close>
```
```  5937
```
```  5938 lemma separating_hyperplane_closed_compact:
```
```  5939   fixes S :: "'a::euclidean_space set"
```
```  5940   assumes "convex S"
```
```  5941     and "closed S"
```
```  5942     and "convex T"
```
```  5943     and "compact T"
```
```  5944     and "T \<noteq> {}"
```
```  5945     and "S \<inter> T = {}"
```
```  5946   shows "\<exists>a b. (\<forall>x\<in>S. inner a x < b) \<and> (\<forall>x\<in>T. inner a x > b)"
```
```  5947 proof (cases "S = {}")
```
```  5948   case True
```
```  5949   obtain b where b: "b > 0" "\<forall>x\<in>T. norm x \<le> b"
```
```  5950     using compact_imp_bounded[OF assms(4)] unfolding bounded_pos by auto
```
```  5951   obtain z :: 'a where z: "norm z = b + 1"
```
```  5952     using vector_choose_size[of "b + 1"] and b(1) by auto
```
```  5953   then have "z \<notin> T" using b(2)[THEN bspec[where x=z]] by auto
```
```  5954   then obtain a b where ab: "inner a z < b" "\<forall>x\<in>T. b < inner a x"
```
```  5955     using separating_hyperplane_closed_point[OF assms(3) compact_imp_closed[OF assms(4)], of z]
```
```  5956     by auto
```
```  5957   then show ?thesis
```
```  5958     using True by auto
```
```  5959 next
```
```  5960   case False
```
```  5961   then obtain y where "y \<in> S" by auto
```
```  5962   obtain a b where "0 < b" "\<forall>x \<in> (\<Union>x\<in> S. \<Union>y \<in> T. {x - y}). b < inner a x"
```
```  5963     using separating_hyperplane_closed_point[OF convex_differences[OF assms(1,3)], of 0]
```
```  5964     using closed_compact_differences[OF assms(2,4)]
```
```  5965     using assms(6) by auto
```
```  5966   then have ab: "\<forall>x\<in>S. \<forall>y\<in>T. b + inner a y < inner a x"
```
```  5967     apply -
```
```  5968     apply rule
```
```  5969     apply rule
```
```  5970     apply (erule_tac x="x - y" in ballE)
```
```  5971     apply (auto simp add: inner_diff)
```
```  5972     done
```
```  5973   define k where "k = (SUP x:T. a \<bullet> x)"
```
```  5974   show ?thesis
```
```  5975     apply (rule_tac x="-a" in exI)
```
```  5976     apply (rule_tac x="-(k + b / 2)" in exI)
```
```  5977     apply (intro conjI ballI)
```
```  5978     unfolding inner_minus_left and neg_less_iff_less
```
```  5979   proof -
```
```  5980     fix x assume "x \<in> T"
```
```  5981     then have "inner a x - b / 2 < k"
```
```  5982       unfolding k_def
```
```  5983     proof (subst less_cSUP_iff)
```
```  5984       show "T \<noteq> {}" by fact
```
```  5985       show "bdd_above ((\<bullet>) a ` T)"
```
```  5986         using ab[rule_format, of y] \<open>y \<in> S\<close>
```
```  5987         by (intro bdd_aboveI2[where M="inner a y - b"]) (auto simp: field_simps intro: less_imp_le)
```
```  5988     qed (auto intro!: bexI[of _ x] \<open>0<b\<close>)
```
```  5989     then show "inner a x < k + b / 2"
```
```  5990       by auto
```
```  5991   next
```
```  5992     fix x
```
```  5993     assume "x \<in> S"
```
```  5994     then have "k \<le> inner a x - b"
```
```  5995       unfolding k_def
```
```  5996       apply (rule_tac cSUP_least)
```
```  5997       using assms(5)
```
```  5998       using ab[THEN bspec[where x=x]]
```
```  5999       apply auto
```
```  6000       done
```
```  6001     then show "k + b / 2 < inner a x"
```
```  6002       using \<open>0 < b\<close> by auto
```
```  6003   qed
```
```  6004 qed
```
```  6005
```
```  6006 lemma separating_hyperplane_compact_closed:
```
```  6007   fixes S :: "'a::euclidean_space set"
```
```  6008   assumes "convex S"
```
```  6009     and "compact S"
```
```  6010     and "S \<noteq> {}"
```
```  6011     and "convex T"
```
```  6012     and "closed T"
```
```  6013     and "S \<inter> T = {}"
```
```  6014   shows "\<exists>a b. (\<forall>x\<in>S. inner a x < b) \<and> (\<forall>x\<in>T. inner a x > b)"
```
```  6015 proof -
```
```  6016   obtain a b where "(\<forall>x\<in>T. inner a x < b) \<and> (\<forall>x\<in>S. b < inner a x)"
```
```  6017     using separating_hyperplane_closed_compact[OF assms(4-5,1-2,3)] and assms(6)
```
```  6018     by auto
```
```  6019   then show ?thesis
```
```  6020     apply (rule_tac x="-a" in exI)
```
```  6021     apply (rule_tac x="-b" in exI)
```
```  6022     apply auto
```
```  6023     done
```
```  6024 qed
```
```  6025
```
```  6026
```
```  6027 subsubsection%unimportant \<open>General case without assuming closure and getting non-strict separation\<close>
```
```  6028
```
```  6029 lemma separating_hyperplane_set_0:
```
```  6030   assumes "convex s" "(0::'a::euclidean_space) \<notin> s"
```
```  6031   shows "\<exists>a. a \<noteq> 0 \<and> (\<forall>x\<in>s. 0 \<le> inner a x)"
```
```  6032 proof -
```
```  6033   let ?k = "\<lambda>c. {x::'a. 0 \<le> inner c x}"
```
```  6034   have *: "frontier (cball 0 1) \<inter> \<Inter>f \<noteq> {}" if as: "f \<subseteq> ?k ` s" "finite f" for f
```
```  6035   proof -
```
```  6036     obtain c where c: "f = ?k ` c" "c \<subseteq> s" "finite c"
```
```  6037       using finite_subset_image[OF as(2,1)] by auto
```
```  6038     then obtain a b where ab: "a \<noteq> 0" "0 < b" "\<forall>x\<in>convex hull c. b < inner a x"
```
```  6039       using separating_hyperplane_closed_0[OF convex_convex_hull, of c]
```
```  6040       using finite_imp_compact_convex_hull[OF c(3), THEN compact_imp_closed] and assms(2)
```
```  6041       using subset_hull[of convex, OF assms(1), symmetric, of c]
```
```  6042       by force
```
```  6043     then have "\<exists>x. norm x = 1 \<and> (\<forall>y\<in>c. 0 \<le> inner y x)"
```
```  6044       apply (rule_tac x = "inverse(norm a) *\<^sub>R a" in exI)
```
```  6045       using hull_subset[of c convex]
```
```  6046       unfolding subset_eq and inner_scaleR
```
```  6047       by (auto simp add: inner_commute del: ballE elim!: ballE)
```
```  6048     then show "frontier (cball 0 1) \<inter> \<Inter>f \<noteq> {}"
```
```  6049       unfolding c(1) frontier_cball sphere_def dist_norm by auto
```
```  6050   qed
```
```  6051   have "frontier (cball 0 1) \<inter> (\<Inter>(?k ` s)) \<noteq> {}"
```
```  6052     apply (rule compact_imp_fip)
```
```  6053     apply (rule compact_frontier[OF compact_cball])
```
```  6054     using * closed_halfspace_ge
```
```  6055     by auto
```
```  6056   then obtain x where "norm x = 1" "\<forall>y\<in>s. x\<in>?k y"
```
```  6057     unfolding frontier_cball dist_norm sphere_def by auto
```
```  6058   then show ?thesis
```
`  6059     by (metis inner_commute mem_Collect_eq nor`