src/HOL/Multivariate_Analysis/Topology_Euclidean_Space.thy
 author haftmann Sat Apr 26 14:53:22 2014 +0200 (2014-04-26) changeset 56742 678a52e676b6 parent 56544 b60d5d119489 child 57275 0ddb5b755cdc permissions -rw-r--r--
more complete classical rules for Inf and Sup, modelled after theiry counterparts on Inter and Union (and INF and SUP)
     1 (*  title:      HOL/Library/Topology_Euclidian_Space.thy

     2     Author:     Amine Chaieb, University of Cambridge

     3     Author:     Robert Himmelmann, TU Muenchen

     4     Author:     Brian Huffman, Portland State University

     5 *)

     6

     7 header {* Elementary topology in Euclidean space. *}

     8

     9 theory Topology_Euclidean_Space

    10 imports

    11   Complex_Main

    12   "~~/src/HOL/Library/Countable_Set"

    13   "~~/src/HOL/Library/FuncSet"

    14   Linear_Algebra

    15   Norm_Arith

    16 begin

    17

    18 lemma dist_0_norm:

    19   fixes x :: "'a::real_normed_vector"

    20   shows "dist 0 x = norm x"

    21 unfolding dist_norm by simp

    22

    23 lemma dist_double: "dist x y < d / 2 \<Longrightarrow> dist x z < d / 2 \<Longrightarrow> dist y z < d"

    24   using dist_triangle[of y z x] by (simp add: dist_commute)

    25

    26 (* LEGACY *)

    27 lemma lim_subseq: "subseq r \<Longrightarrow> s ----> l \<Longrightarrow> (s \<circ> r) ----> l"

    28   by (rule LIMSEQ_subseq_LIMSEQ)

    29

    30 lemma countable_PiE:

    31   "finite I \<Longrightarrow> (\<And>i. i \<in> I \<Longrightarrow> countable (F i)) \<Longrightarrow> countable (PiE I F)"

    32   by (induct I arbitrary: F rule: finite_induct) (auto simp: PiE_insert_eq)

    33

    34 lemma Lim_within_open:

    35   fixes f :: "'a::topological_space \<Rightarrow> 'b::topological_space"

    36   shows "a \<in> S \<Longrightarrow> open S \<Longrightarrow> (f ---> l)(at a within S) \<longleftrightarrow> (f ---> l)(at a)"

    37   by (fact tendsto_within_open)

    38

    39 lemma continuous_on_union:

    40   "closed s \<Longrightarrow> closed t \<Longrightarrow> continuous_on s f \<Longrightarrow> continuous_on t f \<Longrightarrow> continuous_on (s \<union> t) f"

    41   by (fact continuous_on_closed_Un)

    42

    43 lemma continuous_on_cases:

    44   "closed s \<Longrightarrow> closed t \<Longrightarrow> continuous_on s f \<Longrightarrow> continuous_on t g \<Longrightarrow>

    45     \<forall>x. (x\<in>s \<and> \<not> P x) \<or> (x \<in> t \<and> P x) \<longrightarrow> f x = g x \<Longrightarrow>

    46     continuous_on (s \<union> t) (\<lambda>x. if P x then f x else g x)"

    47   by (rule continuous_on_If) auto

    48

    49

    50 subsection {* Topological Basis *}

    51

    52 context topological_space

    53 begin

    54

    55 definition "topological_basis B \<longleftrightarrow>

    56   (\<forall>b\<in>B. open b) \<and> (\<forall>x. open x \<longrightarrow> (\<exists>B'. B' \<subseteq> B \<and> \<Union>B' = x))"

    57

    58 lemma topological_basis:

    59   "topological_basis B \<longleftrightarrow> (\<forall>x. open x \<longleftrightarrow> (\<exists>B'. B' \<subseteq> B \<and> \<Union>B' = x))"

    60   unfolding topological_basis_def

    61   apply safe

    62      apply fastforce

    63     apply fastforce

    64    apply (erule_tac x="x" in allE)

    65    apply simp

    66    apply (rule_tac x="{x}" in exI)

    67   apply auto

    68   done

    69

    70 lemma topological_basis_iff:

    71   assumes "\<And>B'. B' \<in> B \<Longrightarrow> open B'"

    72   shows "topological_basis B \<longleftrightarrow> (\<forall>O'. open O' \<longrightarrow> (\<forall>x\<in>O'. \<exists>B'\<in>B. x \<in> B' \<and> B' \<subseteq> O'))"

    73     (is "_ \<longleftrightarrow> ?rhs")

    74 proof safe

    75   fix O' and x::'a

    76   assume H: "topological_basis B" "open O'" "x \<in> O'"

    77   then have "(\<exists>B'\<subseteq>B. \<Union>B' = O')" by (simp add: topological_basis_def)

    78   then obtain B' where "B' \<subseteq> B" "O' = \<Union>B'" by auto

    79   then show "\<exists>B'\<in>B. x \<in> B' \<and> B' \<subseteq> O'" using H by auto

    80 next

    81   assume H: ?rhs

    82   show "topological_basis B"

    83     using assms unfolding topological_basis_def

    84   proof safe

    85     fix O' :: "'a set"

    86     assume "open O'"

    87     with H obtain f where "\<forall>x\<in>O'. f x \<in> B \<and> x \<in> f x \<and> f x \<subseteq> O'"

    88       by (force intro: bchoice simp: Bex_def)

    89     then show "\<exists>B'\<subseteq>B. \<Union>B' = O'"

    90       by (auto intro: exI[where x="{f x |x. x \<in> O'}"])

    91   qed

    92 qed

    93

    94 lemma topological_basisI:

    95   assumes "\<And>B'. B' \<in> B \<Longrightarrow> open B'"

    96     and "\<And>O' x. open O' \<Longrightarrow> x \<in> O' \<Longrightarrow> \<exists>B'\<in>B. x \<in> B' \<and> B' \<subseteq> O'"

    97   shows "topological_basis B"

    98   using assms by (subst topological_basis_iff) auto

    99

   100 lemma topological_basisE:

   101   fixes O'

   102   assumes "topological_basis B"

   103     and "open O'"

   104     and "x \<in> O'"

   105   obtains B' where "B' \<in> B" "x \<in> B'" "B' \<subseteq> O'"

   106 proof atomize_elim

   107   from assms have "\<And>B'. B'\<in>B \<Longrightarrow> open B'"

   108     by (simp add: topological_basis_def)

   109   with topological_basis_iff assms

   110   show  "\<exists>B'. B' \<in> B \<and> x \<in> B' \<and> B' \<subseteq> O'"

   111     using assms by (simp add: Bex_def)

   112 qed

   113

   114 lemma topological_basis_open:

   115   assumes "topological_basis B"

   116     and "X \<in> B"

   117   shows "open X"

   118   using assms by (simp add: topological_basis_def)

   119

   120 lemma topological_basis_imp_subbasis:

   121   assumes B: "topological_basis B"

   122   shows "open = generate_topology B"

   123 proof (intro ext iffI)

   124   fix S :: "'a set"

   125   assume "open S"

   126   with B obtain B' where "B' \<subseteq> B" "S = \<Union>B'"

   127     unfolding topological_basis_def by blast

   128   then show "generate_topology B S"

   129     by (auto intro: generate_topology.intros dest: topological_basis_open)

   130 next

   131   fix S :: "'a set"

   132   assume "generate_topology B S"

   133   then show "open S"

   134     by induct (auto dest: topological_basis_open[OF B])

   135 qed

   136

   137 lemma basis_dense:

   138   fixes B :: "'a set set"

   139     and f :: "'a set \<Rightarrow> 'a"

   140   assumes "topological_basis B"

   141     and choosefrom_basis: "\<And>B'. B' \<noteq> {} \<Longrightarrow> f B' \<in> B'"

   142   shows "\<forall>X. open X \<longrightarrow> X \<noteq> {} \<longrightarrow> (\<exists>B' \<in> B. f B' \<in> X)"

   143 proof (intro allI impI)

   144   fix X :: "'a set"

   145   assume "open X" and "X \<noteq> {}"

   146   from topological_basisE[OF topological_basis B open X choosefrom_basis[OF X \<noteq> {}]]

   147   obtain B' where "B' \<in> B" "f X \<in> B'" "B' \<subseteq> X" .

   148   then show "\<exists>B'\<in>B. f B' \<in> X"

   149     by (auto intro!: choosefrom_basis)

   150 qed

   151

   152 end

   153

   154 lemma topological_basis_prod:

   155   assumes A: "topological_basis A"

   156     and B: "topological_basis B"

   157   shows "topological_basis ((\<lambda>(a, b). a \<times> b)  (A \<times> B))"

   158   unfolding topological_basis_def

   159 proof (safe, simp_all del: ex_simps add: subset_image_iff ex_simps(1)[symmetric])

   160   fix S :: "('a \<times> 'b) set"

   161   assume "open S"

   162   then show "\<exists>X\<subseteq>A \<times> B. (\<Union>(a,b)\<in>X. a \<times> b) = S"

   163   proof (safe intro!: exI[of _ "{x\<in>A \<times> B. fst x \<times> snd x \<subseteq> S}"])

   164     fix x y

   165     assume "(x, y) \<in> S"

   166     from open_prod_elim[OF open S this]

   167     obtain a b where a: "open a""x \<in> a" and b: "open b" "y \<in> b" and "a \<times> b \<subseteq> S"

   168       by (metis mem_Sigma_iff)

   169     moreover

   170     from A a obtain A0 where "A0 \<in> A" "x \<in> A0" "A0 \<subseteq> a"

   171       by (rule topological_basisE)

   172     moreover

   173     from B b obtain B0 where "B0 \<in> B" "y \<in> B0" "B0 \<subseteq> b"

   174       by (rule topological_basisE)

   175     ultimately show "(x, y) \<in> (\<Union>(a, b)\<in>{X \<in> A \<times> B. fst X \<times> snd X \<subseteq> S}. a \<times> b)"

   176       by (intro UN_I[of "(A0, B0)"]) auto

   177   qed auto

   178 qed (metis A B topological_basis_open open_Times)

   179

   180

   181 subsection {* Countable Basis *}

   182

   183 locale countable_basis =

   184   fixes B :: "'a::topological_space set set"

   185   assumes is_basis: "topological_basis B"

   186     and countable_basis: "countable B"

   187 begin

   188

   189 lemma open_countable_basis_ex:

   190   assumes "open X"

   191   shows "\<exists>B' \<subseteq> B. X = Union B'"

   192   using assms countable_basis is_basis

   193   unfolding topological_basis_def by blast

   194

   195 lemma open_countable_basisE:

   196   assumes "open X"

   197   obtains B' where "B' \<subseteq> B" "X = Union B'"

   198   using assms open_countable_basis_ex

   199   by (atomize_elim) simp

   200

   201 lemma countable_dense_exists:

   202   "\<exists>D::'a set. countable D \<and> (\<forall>X. open X \<longrightarrow> X \<noteq> {} \<longrightarrow> (\<exists>d \<in> D. d \<in> X))"

   203 proof -

   204   let ?f = "(\<lambda>B'. SOME x. x \<in> B')"

   205   have "countable (?f  B)" using countable_basis by simp

   206   with basis_dense[OF is_basis, of ?f] show ?thesis

   207     by (intro exI[where x="?f  B"]) (metis (mono_tags) all_not_in_conv imageI someI)

   208 qed

   209

   210 lemma countable_dense_setE:

   211   obtains D :: "'a set"

   212   where "countable D" "\<And>X. open X \<Longrightarrow> X \<noteq> {} \<Longrightarrow> \<exists>d \<in> D. d \<in> X"

   213   using countable_dense_exists by blast

   214

   215 end

   216

   217 lemma (in first_countable_topology) first_countable_basisE:

   218   obtains A where "countable A" "\<And>a. a \<in> A \<Longrightarrow> x \<in> a" "\<And>a. a \<in> A \<Longrightarrow> open a"

   219     "\<And>S. open S \<Longrightarrow> x \<in> S \<Longrightarrow> (\<exists>a\<in>A. a \<subseteq> S)"

   220   using first_countable_basis[of x]

   221   apply atomize_elim

   222   apply (elim exE)

   223   apply (rule_tac x="range A" in exI)

   224   apply auto

   225   done

   226

   227 lemma (in first_countable_topology) first_countable_basis_Int_stableE:

   228   obtains A where "countable A" "\<And>a. a \<in> A \<Longrightarrow> x \<in> a" "\<And>a. a \<in> A \<Longrightarrow> open a"

   229     "\<And>S. open S \<Longrightarrow> x \<in> S \<Longrightarrow> (\<exists>a\<in>A. a \<subseteq> S)"

   230     "\<And>a b. a \<in> A \<Longrightarrow> b \<in> A \<Longrightarrow> a \<inter> b \<in> A"

   231 proof atomize_elim

   232   obtain A' where A':

   233     "countable A'"

   234     "\<And>a. a \<in> A' \<Longrightarrow> x \<in> a"

   235     "\<And>a. a \<in> A' \<Longrightarrow> open a"

   236     "\<And>S. open S \<Longrightarrow> x \<in> S \<Longrightarrow> \<exists>a\<in>A'. a \<subseteq> S"

   237     by (rule first_countable_basisE) blast

   238   def A \<equiv> "(\<lambda>N. \<Inter>((\<lambda>n. from_nat_into A' n)  N))  (Collect finite::nat set set)"

   239   then show "\<exists>A. countable A \<and> (\<forall>a. a \<in> A \<longrightarrow> x \<in> a) \<and> (\<forall>a. a \<in> A \<longrightarrow> open a) \<and>

   240         (\<forall>S. open S \<longrightarrow> x \<in> S \<longrightarrow> (\<exists>a\<in>A. a \<subseteq> S)) \<and> (\<forall>a b. a \<in> A \<longrightarrow> b \<in> A \<longrightarrow> a \<inter> b \<in> A)"

   241   proof (safe intro!: exI[where x=A])

   242     show "countable A"

   243       unfolding A_def by (intro countable_image countable_Collect_finite)

   244     fix a

   245     assume "a \<in> A"

   246     then show "x \<in> a" "open a"

   247       using A'(4)[OF open_UNIV] by (auto simp: A_def intro: A' from_nat_into)

   248   next

   249     let ?int = "\<lambda>N. \<Inter>(from_nat_into A'  N)"

   250     fix a b

   251     assume "a \<in> A" "b \<in> A"

   252     then obtain N M where "a = ?int N" "b = ?int M" "finite (N \<union> M)"

   253       by (auto simp: A_def)

   254     then show "a \<inter> b \<in> A"

   255       by (auto simp: A_def intro!: image_eqI[where x="N \<union> M"])

   256   next

   257     fix S

   258     assume "open S" "x \<in> S"

   259     then obtain a where a: "a\<in>A'" "a \<subseteq> S" using A' by blast

   260     then show "\<exists>a\<in>A. a \<subseteq> S" using a A'

   261       by (intro bexI[where x=a]) (auto simp: A_def intro: image_eqI[where x="{to_nat_on A' a}"])

   262   qed

   263 qed

   264

   265 lemma (in topological_space) first_countableI:

   266   assumes "countable A"

   267     and 1: "\<And>a. a \<in> A \<Longrightarrow> x \<in> a" "\<And>a. a \<in> A \<Longrightarrow> open a"

   268     and 2: "\<And>S. open S \<Longrightarrow> x \<in> S \<Longrightarrow> \<exists>a\<in>A. a \<subseteq> S"

   269   shows "\<exists>A::nat \<Rightarrow> 'a set. (\<forall>i. x \<in> A i \<and> open (A i)) \<and> (\<forall>S. open S \<and> x \<in> S \<longrightarrow> (\<exists>i. A i \<subseteq> S))"

   270 proof (safe intro!: exI[of _ "from_nat_into A"])

   271   fix i

   272   have "A \<noteq> {}" using 2[of UNIV] by auto

   273   show "x \<in> from_nat_into A i" "open (from_nat_into A i)"

   274     using range_from_nat_into_subset[OF A \<noteq> {}] 1 by auto

   275 next

   276   fix S

   277   assume "open S" "x\<in>S" from 2[OF this]

   278   show "\<exists>i. from_nat_into A i \<subseteq> S"

   279     using subset_range_from_nat_into[OF countable A] by auto

   280 qed

   281

   282 instance prod :: (first_countable_topology, first_countable_topology) first_countable_topology

   283 proof

   284   fix x :: "'a \<times> 'b"

   285   obtain A where A:

   286       "countable A"

   287       "\<And>a. a \<in> A \<Longrightarrow> fst x \<in> a"

   288       "\<And>a. a \<in> A \<Longrightarrow> open a"

   289       "\<And>S. open S \<Longrightarrow> fst x \<in> S \<Longrightarrow> \<exists>a\<in>A. a \<subseteq> S"

   290     by (rule first_countable_basisE[of "fst x"]) blast

   291   obtain B where B:

   292       "countable B"

   293       "\<And>a. a \<in> B \<Longrightarrow> snd x \<in> a"

   294       "\<And>a. a \<in> B \<Longrightarrow> open a"

   295       "\<And>S. open S \<Longrightarrow> snd x \<in> S \<Longrightarrow> \<exists>a\<in>B. a \<subseteq> S"

   296     by (rule first_countable_basisE[of "snd x"]) blast

   297   show "\<exists>A::nat \<Rightarrow> ('a \<times> 'b) set.

   298     (\<forall>i. x \<in> A i \<and> open (A i)) \<and> (\<forall>S. open S \<and> x \<in> S \<longrightarrow> (\<exists>i. A i \<subseteq> S))"

   299   proof (rule first_countableI[of "(\<lambda>(a, b). a \<times> b)  (A \<times> B)"], safe)

   300     fix a b

   301     assume x: "a \<in> A" "b \<in> B"

   302     with A(2, 3)[of a] B(2, 3)[of b] show "x \<in> a \<times> b" and "open (a \<times> b)"

   303       unfolding mem_Times_iff

   304       by (auto intro: open_Times)

   305   next

   306     fix S

   307     assume "open S" "x \<in> S"

   308     then obtain a' b' where a'b': "open a'" "open b'" "x \<in> a' \<times> b'" "a' \<times> b' \<subseteq> S"

   309       by (rule open_prod_elim)

   310     moreover

   311     from a'b' A(4)[of a'] B(4)[of b']

   312     obtain a b where "a \<in> A" "a \<subseteq> a'" "b \<in> B" "b \<subseteq> b'"

   313       by auto

   314     ultimately

   315     show "\<exists>a\<in>(\<lambda>(a, b). a \<times> b)  (A \<times> B). a \<subseteq> S"

   316       by (auto intro!: bexI[of _ "a \<times> b"] bexI[of _ a] bexI[of _ b])

   317   qed (simp add: A B)

   318 qed

   319

   320 class second_countable_topology = topological_space +

   321   assumes ex_countable_subbasis:

   322     "\<exists>B::'a::topological_space set set. countable B \<and> open = generate_topology B"

   323 begin

   324

   325 lemma ex_countable_basis: "\<exists>B::'a set set. countable B \<and> topological_basis B"

   326 proof -

   327   from ex_countable_subbasis obtain B where B: "countable B" "open = generate_topology B"

   328     by blast

   329   let ?B = "Inter  {b. finite b \<and> b \<subseteq> B }"

   330

   331   show ?thesis

   332   proof (intro exI conjI)

   333     show "countable ?B"

   334       by (intro countable_image countable_Collect_finite_subset B)

   335     {

   336       fix S

   337       assume "open S"

   338       then have "\<exists>B'\<subseteq>{b. finite b \<and> b \<subseteq> B}. (\<Union>b\<in>B'. \<Inter>b) = S"

   339         unfolding B

   340       proof induct

   341         case UNIV

   342         show ?case by (intro exI[of _ "{{}}"]) simp

   343       next

   344         case (Int a b)

   345         then obtain x y where x: "a = UNION x Inter" "\<And>i. i \<in> x \<Longrightarrow> finite i \<and> i \<subseteq> B"

   346           and y: "b = UNION y Inter" "\<And>i. i \<in> y \<Longrightarrow> finite i \<and> i \<subseteq> B"

   347           by blast

   348         show ?case

   349           unfolding x y Int_UN_distrib2

   350           by (intro exI[of _ "{i \<union> j| i j.  i \<in> x \<and> j \<in> y}"]) (auto dest: x(2) y(2))

   351       next

   352         case (UN K)

   353         then have "\<forall>k\<in>K. \<exists>B'\<subseteq>{b. finite b \<and> b \<subseteq> B}. UNION B' Inter = k" by auto

   354         then obtain k where

   355             "\<forall>ka\<in>K. k ka \<subseteq> {b. finite b \<and> b \<subseteq> B} \<and> UNION (k ka) Inter = ka"

   356           unfolding bchoice_iff ..

   357         then show "\<exists>B'\<subseteq>{b. finite b \<and> b \<subseteq> B}. UNION B' Inter = \<Union>K"

   358           by (intro exI[of _ "UNION K k"]) auto

   359       next

   360         case (Basis S)

   361         then show ?case

   362           by (intro exI[of _ "{{S}}"]) auto

   363       qed

   364       then have "(\<exists>B'\<subseteq>Inter  {b. finite b \<and> b \<subseteq> B}. \<Union>B' = S)"

   365         unfolding subset_image_iff by blast }

   366     then show "topological_basis ?B"

   367       unfolding topological_space_class.topological_basis_def

   368       by (safe intro!: topological_space_class.open_Inter)

   369          (simp_all add: B generate_topology.Basis subset_eq)

   370   qed

   371 qed

   372

   373 end

   374

   375 sublocale second_countable_topology <

   376   countable_basis "SOME B. countable B \<and> topological_basis B"

   377   using someI_ex[OF ex_countable_basis]

   378   by unfold_locales safe

   379

   380 instance prod :: (second_countable_topology, second_countable_topology) second_countable_topology

   381 proof

   382   obtain A :: "'a set set" where "countable A" "topological_basis A"

   383     using ex_countable_basis by auto

   384   moreover

   385   obtain B :: "'b set set" where "countable B" "topological_basis B"

   386     using ex_countable_basis by auto

   387   ultimately show "\<exists>B::('a \<times> 'b) set set. countable B \<and> open = generate_topology B"

   388     by (auto intro!: exI[of _ "(\<lambda>(a, b). a \<times> b)  (A \<times> B)"] topological_basis_prod

   389       topological_basis_imp_subbasis)

   390 qed

   391

   392 instance second_countable_topology \<subseteq> first_countable_topology

   393 proof

   394   fix x :: 'a

   395   def B \<equiv> "SOME B::'a set set. countable B \<and> topological_basis B"

   396   then have B: "countable B" "topological_basis B"

   397     using countable_basis is_basis

   398     by (auto simp: countable_basis is_basis)

   399   then show "\<exists>A::nat \<Rightarrow> 'a set.

   400     (\<forall>i. x \<in> A i \<and> open (A i)) \<and> (\<forall>S. open S \<and> x \<in> S \<longrightarrow> (\<exists>i. A i \<subseteq> S))"

   401     by (intro first_countableI[of "{b\<in>B. x \<in> b}"])

   402        (fastforce simp: topological_space_class.topological_basis_def)+

   403 qed

   404

   405

   406 subsection {* Polish spaces *}

   407

   408 text {* Textbooks define Polish spaces as completely metrizable.

   409   We assume the topology to be complete for a given metric. *}

   410

   411 class polish_space = complete_space + second_countable_topology

   412

   413 subsection {* General notion of a topology as a value *}

   414

   415 definition "istopology L \<longleftrightarrow>

   416   L {} \<and> (\<forall>S T. L S \<longrightarrow> L T \<longrightarrow> L (S \<inter> T)) \<and> (\<forall>K. Ball K L \<longrightarrow> L (\<Union> K))"

   417

   418 typedef 'a topology = "{L::('a set) \<Rightarrow> bool. istopology L}"

   419   morphisms "openin" "topology"

   420   unfolding istopology_def by blast

   421

   422 lemma istopology_open_in[intro]: "istopology(openin U)"

   423   using openin[of U] by blast

   424

   425 lemma topology_inverse': "istopology U \<Longrightarrow> openin (topology U) = U"

   426   using topology_inverse[unfolded mem_Collect_eq] .

   427

   428 lemma topology_inverse_iff: "istopology U \<longleftrightarrow> openin (topology U) = U"

   429   using topology_inverse[of U] istopology_open_in[of "topology U"] by auto

   430

   431 lemma topology_eq: "T1 = T2 \<longleftrightarrow> (\<forall>S. openin T1 S \<longleftrightarrow> openin T2 S)"

   432 proof

   433   assume "T1 = T2"

   434   then show "\<forall>S. openin T1 S \<longleftrightarrow> openin T2 S" by simp

   435 next

   436   assume H: "\<forall>S. openin T1 S \<longleftrightarrow> openin T2 S"

   437   then have "openin T1 = openin T2" by (simp add: fun_eq_iff)

   438   then have "topology (openin T1) = topology (openin T2)" by simp

   439   then show "T1 = T2" unfolding openin_inverse .

   440 qed

   441

   442 text{* Infer the "universe" from union of all sets in the topology. *}

   443

   444 definition "topspace T = \<Union>{S. openin T S}"

   445

   446 subsubsection {* Main properties of open sets *}

   447

   448 lemma openin_clauses:

   449   fixes U :: "'a topology"

   450   shows

   451     "openin U {}"

   452     "\<And>S T. openin U S \<Longrightarrow> openin U T \<Longrightarrow> openin U (S\<inter>T)"

   453     "\<And>K. (\<forall>S \<in> K. openin U S) \<Longrightarrow> openin U (\<Union>K)"

   454   using openin[of U] unfolding istopology_def mem_Collect_eq by fast+

   455

   456 lemma openin_subset[intro]: "openin U S \<Longrightarrow> S \<subseteq> topspace U"

   457   unfolding topspace_def by blast

   458

   459 lemma openin_empty[simp]: "openin U {}"

   460   by (simp add: openin_clauses)

   461

   462 lemma openin_Int[intro]: "openin U S \<Longrightarrow> openin U T \<Longrightarrow> openin U (S \<inter> T)"

   463   using openin_clauses by simp

   464

   465 lemma openin_Union[intro]: "(\<forall>S \<in>K. openin U S) \<Longrightarrow> openin U (\<Union> K)"

   466   using openin_clauses by simp

   467

   468 lemma openin_Un[intro]: "openin U S \<Longrightarrow> openin U T \<Longrightarrow> openin U (S \<union> T)"

   469   using openin_Union[of "{S,T}" U] by auto

   470

   471 lemma openin_topspace[intro, simp]: "openin U (topspace U)"

   472   by (simp add: openin_Union topspace_def)

   473

   474 lemma openin_subopen: "openin U S \<longleftrightarrow> (\<forall>x \<in> S. \<exists>T. openin U T \<and> x \<in> T \<and> T \<subseteq> S)"

   475   (is "?lhs \<longleftrightarrow> ?rhs")

   476 proof

   477   assume ?lhs

   478   then show ?rhs by auto

   479 next

   480   assume H: ?rhs

   481   let ?t = "\<Union>{T. openin U T \<and> T \<subseteq> S}"

   482   have "openin U ?t" by (simp add: openin_Union)

   483   also have "?t = S" using H by auto

   484   finally show "openin U S" .

   485 qed

   486

   487

   488 subsubsection {* Closed sets *}

   489

   490 definition "closedin U S \<longleftrightarrow> S \<subseteq> topspace U \<and> openin U (topspace U - S)"

   491

   492 lemma closedin_subset: "closedin U S \<Longrightarrow> S \<subseteq> topspace U"

   493   by (metis closedin_def)

   494

   495 lemma closedin_empty[simp]: "closedin U {}"

   496   by (simp add: closedin_def)

   497

   498 lemma closedin_topspace[intro, simp]: "closedin U (topspace U)"

   499   by (simp add: closedin_def)

   500

   501 lemma closedin_Un[intro]: "closedin U S \<Longrightarrow> closedin U T \<Longrightarrow> closedin U (S \<union> T)"

   502   by (auto simp add: Diff_Un closedin_def)

   503

   504 lemma Diff_Inter[intro]: "A - \<Inter>S = \<Union> {A - s|s. s\<in>S}"

   505   by auto

   506

   507 lemma closedin_Inter[intro]:

   508   assumes Ke: "K \<noteq> {}"

   509     and Kc: "\<forall>S \<in>K. closedin U S"

   510   shows "closedin U (\<Inter> K)"

   511   using Ke Kc unfolding closedin_def Diff_Inter by auto

   512

   513 lemma closedin_Int[intro]: "closedin U S \<Longrightarrow> closedin U T \<Longrightarrow> closedin U (S \<inter> T)"

   514   using closedin_Inter[of "{S,T}" U] by auto

   515

   516 lemma Diff_Diff_Int: "A - (A - B) = A \<inter> B"

   517   by blast

   518

   519 lemma openin_closedin_eq: "openin U S \<longleftrightarrow> S \<subseteq> topspace U \<and> closedin U (topspace U - S)"

   520   apply (auto simp add: closedin_def Diff_Diff_Int inf_absorb2)

   521   apply (metis openin_subset subset_eq)

   522   done

   523

   524 lemma openin_closedin: "S \<subseteq> topspace U \<Longrightarrow> (openin U S \<longleftrightarrow> closedin U (topspace U - S))"

   525   by (simp add: openin_closedin_eq)

   526

   527 lemma openin_diff[intro]:

   528   assumes oS: "openin U S"

   529     and cT: "closedin U T"

   530   shows "openin U (S - T)"

   531 proof -

   532   have "S - T = S \<inter> (topspace U - T)" using openin_subset[of U S]  oS cT

   533     by (auto simp add: topspace_def openin_subset)

   534   then show ?thesis using oS cT

   535     by (auto simp add: closedin_def)

   536 qed

   537

   538 lemma closedin_diff[intro]:

   539   assumes oS: "closedin U S"

   540     and cT: "openin U T"

   541   shows "closedin U (S - T)"

   542 proof -

   543   have "S - T = S \<inter> (topspace U - T)"

   544     using closedin_subset[of U S] oS cT by (auto simp add: topspace_def)

   545   then show ?thesis

   546     using oS cT by (auto simp add: openin_closedin_eq)

   547 qed

   548

   549

   550 subsubsection {* Subspace topology *}

   551

   552 definition "subtopology U V = topology (\<lambda>T. \<exists>S. T = S \<inter> V \<and> openin U S)"

   553

   554 lemma istopology_subtopology: "istopology (\<lambda>T. \<exists>S. T = S \<inter> V \<and> openin U S)"

   555   (is "istopology ?L")

   556 proof -

   557   have "?L {}" by blast

   558   {

   559     fix A B

   560     assume A: "?L A" and B: "?L B"

   561     from A B obtain Sa and Sb where Sa: "openin U Sa" "A = Sa \<inter> V" and Sb: "openin U Sb" "B = Sb \<inter> V"

   562       by blast

   563     have "A \<inter> B = (Sa \<inter> Sb) \<inter> V" "openin U (Sa \<inter> Sb)"

   564       using Sa Sb by blast+

   565     then have "?L (A \<inter> B)" by blast

   566   }

   567   moreover

   568   {

   569     fix K

   570     assume K: "K \<subseteq> Collect ?L"

   571     have th0: "Collect ?L = (\<lambda>S. S \<inter> V)  Collect (openin U)"

   572       by blast

   573     from K[unfolded th0 subset_image_iff]

   574     obtain Sk where Sk: "Sk \<subseteq> Collect (openin U)" "K = (\<lambda>S. S \<inter> V)  Sk"

   575       by blast

   576     have "\<Union>K = (\<Union>Sk) \<inter> V"

   577       using Sk by auto

   578     moreover have "openin U (\<Union> Sk)"

   579       using Sk by (auto simp add: subset_eq)

   580     ultimately have "?L (\<Union>K)" by blast

   581   }

   582   ultimately show ?thesis

   583     unfolding subset_eq mem_Collect_eq istopology_def by blast

   584 qed

   585

   586 lemma openin_subtopology: "openin (subtopology U V) S \<longleftrightarrow> (\<exists>T. openin U T \<and> S = T \<inter> V)"

   587   unfolding subtopology_def topology_inverse'[OF istopology_subtopology]

   588   by auto

   589

   590 lemma topspace_subtopology: "topspace (subtopology U V) = topspace U \<inter> V"

   591   by (auto simp add: topspace_def openin_subtopology)

   592

   593 lemma closedin_subtopology: "closedin (subtopology U V) S \<longleftrightarrow> (\<exists>T. closedin U T \<and> S = T \<inter> V)"

   594   unfolding closedin_def topspace_subtopology

   595   by (auto simp add: openin_subtopology)

   596

   597 lemma openin_subtopology_refl: "openin (subtopology U V) V \<longleftrightarrow> V \<subseteq> topspace U"

   598   unfolding openin_subtopology

   599   by auto (metis IntD1 in_mono openin_subset)

   600

   601 lemma subtopology_superset:

   602   assumes UV: "topspace U \<subseteq> V"

   603   shows "subtopology U V = U"

   604 proof -

   605   {

   606     fix S

   607     {

   608       fix T

   609       assume T: "openin U T" "S = T \<inter> V"

   610       from T openin_subset[OF T(1)] UV have eq: "S = T"

   611         by blast

   612       have "openin U S"

   613         unfolding eq using T by blast

   614     }

   615     moreover

   616     {

   617       assume S: "openin U S"

   618       then have "\<exists>T. openin U T \<and> S = T \<inter> V"

   619         using openin_subset[OF S] UV by auto

   620     }

   621     ultimately have "(\<exists>T. openin U T \<and> S = T \<inter> V) \<longleftrightarrow> openin U S"

   622       by blast

   623   }

   624   then show ?thesis

   625     unfolding topology_eq openin_subtopology by blast

   626 qed

   627

   628 lemma subtopology_topspace[simp]: "subtopology U (topspace U) = U"

   629   by (simp add: subtopology_superset)

   630

   631 lemma subtopology_UNIV[simp]: "subtopology U UNIV = U"

   632   by (simp add: subtopology_superset)

   633

   634

   635 subsubsection {* The standard Euclidean topology *}

   636

   637 definition euclidean :: "'a::topological_space topology"

   638   where "euclidean = topology open"

   639

   640 lemma open_openin: "open S \<longleftrightarrow> openin euclidean S"

   641   unfolding euclidean_def

   642   apply (rule cong[where x=S and y=S])

   643   apply (rule topology_inverse[symmetric])

   644   apply (auto simp add: istopology_def)

   645   done

   646

   647 lemma topspace_euclidean: "topspace euclidean = UNIV"

   648   apply (simp add: topspace_def)

   649   apply (rule set_eqI)

   650   apply (auto simp add: open_openin[symmetric])

   651   done

   652

   653 lemma topspace_euclidean_subtopology[simp]: "topspace (subtopology euclidean S) = S"

   654   by (simp add: topspace_euclidean topspace_subtopology)

   655

   656 lemma closed_closedin: "closed S \<longleftrightarrow> closedin euclidean S"

   657   by (simp add: closed_def closedin_def topspace_euclidean open_openin Compl_eq_Diff_UNIV)

   658

   659 lemma open_subopen: "open S \<longleftrightarrow> (\<forall>x\<in>S. \<exists>T. open T \<and> x \<in> T \<and> T \<subseteq> S)"

   660   by (simp add: open_openin openin_subopen[symmetric])

   661

   662 text {* Basic "localization" results are handy for connectedness. *}

   663

   664 lemma openin_open: "openin (subtopology euclidean U) S \<longleftrightarrow> (\<exists>T. open T \<and> (S = U \<inter> T))"

   665   by (auto simp add: openin_subtopology open_openin[symmetric])

   666

   667 lemma openin_open_Int[intro]: "open S \<Longrightarrow> openin (subtopology euclidean U) (U \<inter> S)"

   668   by (auto simp add: openin_open)

   669

   670 lemma open_openin_trans[trans]:

   671   "open S \<Longrightarrow> open T \<Longrightarrow> T \<subseteq> S \<Longrightarrow> openin (subtopology euclidean S) T"

   672   by (metis Int_absorb1  openin_open_Int)

   673

   674 lemma open_subset: "S \<subseteq> T \<Longrightarrow> open S \<Longrightarrow> openin (subtopology euclidean T) S"

   675   by (auto simp add: openin_open)

   676

   677 lemma closedin_closed: "closedin (subtopology euclidean U) S \<longleftrightarrow> (\<exists>T. closed T \<and> S = U \<inter> T)"

   678   by (simp add: closedin_subtopology closed_closedin Int_ac)

   679

   680 lemma closedin_closed_Int: "closed S \<Longrightarrow> closedin (subtopology euclidean U) (U \<inter> S)"

   681   by (metis closedin_closed)

   682

   683 lemma closed_closedin_trans:

   684   "closed S \<Longrightarrow> closed T \<Longrightarrow> T \<subseteq> S \<Longrightarrow> closedin (subtopology euclidean S) T"

   685   by (metis closedin_closed inf.absorb2)

   686

   687 lemma closed_subset: "S \<subseteq> T \<Longrightarrow> closed S \<Longrightarrow> closedin (subtopology euclidean T) S"

   688   by (auto simp add: closedin_closed)

   689

   690 lemma openin_euclidean_subtopology_iff:

   691   fixes S U :: "'a::metric_space set"

   692   shows "openin (subtopology euclidean U) S \<longleftrightarrow>

   693     S \<subseteq> U \<and> (\<forall>x\<in>S. \<exists>e>0. \<forall>x'\<in>U. dist x' x < e \<longrightarrow> x'\<in> S)"

   694   (is "?lhs \<longleftrightarrow> ?rhs")

   695 proof

   696   assume ?lhs

   697   then show ?rhs

   698     unfolding openin_open open_dist by blast

   699 next

   700   def T \<equiv> "{x. \<exists>a\<in>S. \<exists>d>0. (\<forall>y\<in>U. dist y a < d \<longrightarrow> y \<in> S) \<and> dist x a < d}"

   701   have 1: "\<forall>x\<in>T. \<exists>e>0. \<forall>y. dist y x < e \<longrightarrow> y \<in> T"

   702     unfolding T_def

   703     apply clarsimp

   704     apply (rule_tac x="d - dist x a" in exI)

   705     apply (clarsimp simp add: less_diff_eq)

   706     by (metis dist_commute dist_triangle_lt)

   707   assume ?rhs then have 2: "S = U \<inter> T"

   708     unfolding T_def

   709     by auto (metis dist_self)

   710   from 1 2 show ?lhs

   711     unfolding openin_open open_dist by fast

   712 qed

   713

   714 text {* These "transitivity" results are handy too *}

   715

   716 lemma openin_trans[trans]:

   717   "openin (subtopology euclidean T) S \<Longrightarrow> openin (subtopology euclidean U) T \<Longrightarrow>

   718     openin (subtopology euclidean U) S"

   719   unfolding open_openin openin_open by blast

   720

   721 lemma openin_open_trans: "openin (subtopology euclidean T) S \<Longrightarrow> open T \<Longrightarrow> open S"

   722   by (auto simp add: openin_open intro: openin_trans)

   723

   724 lemma closedin_trans[trans]:

   725   "closedin (subtopology euclidean T) S \<Longrightarrow> closedin (subtopology euclidean U) T \<Longrightarrow>

   726     closedin (subtopology euclidean U) S"

   727   by (auto simp add: closedin_closed closed_closedin closed_Inter Int_assoc)

   728

   729 lemma closedin_closed_trans: "closedin (subtopology euclidean T) S \<Longrightarrow> closed T \<Longrightarrow> closed S"

   730   by (auto simp add: closedin_closed intro: closedin_trans)

   731

   732

   733 subsection {* Open and closed balls *}

   734

   735 definition ball :: "'a::metric_space \<Rightarrow> real \<Rightarrow> 'a set"

   736   where "ball x e = {y. dist x y < e}"

   737

   738 definition cball :: "'a::metric_space \<Rightarrow> real \<Rightarrow> 'a set"

   739   where "cball x e = {y. dist x y \<le> e}"

   740

   741 lemma mem_ball [simp]: "y \<in> ball x e \<longleftrightarrow> dist x y < e"

   742   by (simp add: ball_def)

   743

   744 lemma mem_cball [simp]: "y \<in> cball x e \<longleftrightarrow> dist x y \<le> e"

   745   by (simp add: cball_def)

   746

   747 lemma mem_ball_0:

   748   fixes x :: "'a::real_normed_vector"

   749   shows "x \<in> ball 0 e \<longleftrightarrow> norm x < e"

   750   by (simp add: dist_norm)

   751

   752 lemma mem_cball_0:

   753   fixes x :: "'a::real_normed_vector"

   754   shows "x \<in> cball 0 e \<longleftrightarrow> norm x \<le> e"

   755   by (simp add: dist_norm)

   756

   757 lemma centre_in_ball: "x \<in> ball x e \<longleftrightarrow> 0 < e"

   758   by simp

   759

   760 lemma centre_in_cball: "x \<in> cball x e \<longleftrightarrow> 0 \<le> e"

   761   by simp

   762

   763 lemma ball_subset_cball[simp,intro]: "ball x e \<subseteq> cball x e"

   764   by (simp add: subset_eq)

   765

   766 lemma subset_ball[intro]: "d \<le> e \<Longrightarrow> ball x d \<subseteq> ball x e"

   767   by (simp add: subset_eq)

   768

   769 lemma subset_cball[intro]: "d \<le> e \<Longrightarrow> cball x d \<subseteq> cball x e"

   770   by (simp add: subset_eq)

   771

   772 lemma ball_max_Un: "ball a (max r s) = ball a r \<union> ball a s"

   773   by (simp add: set_eq_iff) arith

   774

   775 lemma ball_min_Int: "ball a (min r s) = ball a r \<inter> ball a s"

   776   by (simp add: set_eq_iff)

   777

   778 lemma diff_less_iff:

   779   "(a::real) - b > 0 \<longleftrightarrow> a > b"

   780   "(a::real) - b < 0 \<longleftrightarrow> a < b"

   781   "a - b < c \<longleftrightarrow> a < c + b" "a - b > c \<longleftrightarrow> a > c + b"

   782   by arith+

   783

   784 lemma diff_le_iff:

   785   "(a::real) - b \<ge> 0 \<longleftrightarrow> a \<ge> b"

   786   "(a::real) - b \<le> 0 \<longleftrightarrow> a \<le> b"

   787   "a - b \<le> c \<longleftrightarrow> a \<le> c + b"

   788   "a - b \<ge> c \<longleftrightarrow> a \<ge> c + b"

   789   by arith+

   790

   791 lemma open_ball [intro, simp]: "open (ball x e)"

   792 proof -

   793   have "open (dist x - {..<e})"

   794     by (intro open_vimage open_lessThan continuous_intros)

   795   also have "dist x - {..<e} = ball x e"

   796     by auto

   797   finally show ?thesis .

   798 qed

   799

   800 lemma open_contains_ball: "open S \<longleftrightarrow> (\<forall>x\<in>S. \<exists>e>0. ball x e \<subseteq> S)"

   801   unfolding open_dist subset_eq mem_ball Ball_def dist_commute ..

   802

   803 lemma openE[elim?]:

   804   assumes "open S" "x\<in>S"

   805   obtains e where "e>0" "ball x e \<subseteq> S"

   806   using assms unfolding open_contains_ball by auto

   807

   808 lemma open_contains_ball_eq: "open S \<Longrightarrow> \<forall>x. x\<in>S \<longleftrightarrow> (\<exists>e>0. ball x e \<subseteq> S)"

   809   by (metis open_contains_ball subset_eq centre_in_ball)

   810

   811 lemma ball_eq_empty[simp]: "ball x e = {} \<longleftrightarrow> e \<le> 0"

   812   unfolding mem_ball set_eq_iff

   813   apply (simp add: not_less)

   814   apply (metis zero_le_dist order_trans dist_self)

   815   done

   816

   817 lemma ball_empty[intro]: "e \<le> 0 \<Longrightarrow> ball x e = {}" by simp

   818

   819 lemma euclidean_dist_l2:

   820   fixes x y :: "'a :: euclidean_space"

   821   shows "dist x y = setL2 (\<lambda>i. dist (x \<bullet> i) (y \<bullet> i)) Basis"

   822   unfolding dist_norm norm_eq_sqrt_inner setL2_def

   823   by (subst euclidean_inner) (simp add: power2_eq_square inner_diff_left)

   824

   825

   826 subsection {* Boxes *}

   827

   828 definition (in euclidean_space) eucl_less (infix "<e" 50)

   829   where "eucl_less a b \<longleftrightarrow> (\<forall>i\<in>Basis. a \<bullet> i < b \<bullet> i)"

   830

   831 definition box_eucl_less: "box a b = {x. a <e x \<and> x <e b}"

   832 definition "cbox a b = {x. \<forall>i\<in>Basis. a \<bullet> i \<le> x \<bullet> i \<and> x \<bullet> i \<le> b \<bullet> i}"

   833

   834 lemma box_def: "box a b = {x. \<forall>i\<in>Basis. a \<bullet> i < x \<bullet> i \<and> x \<bullet> i < b \<bullet> i}"

   835   and in_box_eucl_less: "x \<in> box a b \<longleftrightarrow> a <e x \<and> x <e b"

   836   and mem_box: "x \<in> box a b \<longleftrightarrow> (\<forall>i\<in>Basis. a \<bullet> i < x \<bullet> i \<and> x \<bullet> i < b \<bullet> i)"

   837     "x \<in> cbox a b \<longleftrightarrow> (\<forall>i\<in>Basis. a \<bullet> i \<le> x \<bullet> i \<and> x \<bullet> i \<le> b \<bullet> i)"

   838   by (auto simp: box_eucl_less eucl_less_def cbox_def)

   839

   840 lemma mem_box_real[simp]:

   841   "(x::real) \<in> box a b \<longleftrightarrow> a < x \<and> x < b"

   842   "(x::real) \<in> cbox a b \<longleftrightarrow> a \<le> x \<and> x \<le> b"

   843   by (auto simp: mem_box)

   844

   845 lemma box_real[simp]:

   846   fixes a b:: real

   847   shows "box a b = {a <..< b}" "cbox a b = {a .. b}"

   848   by auto

   849

   850 lemma rational_boxes:

   851   fixes x :: "'a\<Colon>euclidean_space"

   852   assumes "e > 0"

   853   shows "\<exists>a b. (\<forall>i\<in>Basis. a \<bullet> i \<in> \<rat> \<and> b \<bullet> i \<in> \<rat> ) \<and> x \<in> box a b \<and> box a b \<subseteq> ball x e"

   854 proof -

   855   def e' \<equiv> "e / (2 * sqrt (real (DIM ('a))))"

   856   then have e: "e' > 0"

   857     using assms by (auto simp: DIM_positive)

   858   have "\<forall>i. \<exists>y. y \<in> \<rat> \<and> y < x \<bullet> i \<and> x \<bullet> i - y < e'" (is "\<forall>i. ?th i")

   859   proof

   860     fix i

   861     from Rats_dense_in_real[of "x \<bullet> i - e'" "x \<bullet> i"] e

   862     show "?th i" by auto

   863   qed

   864   from choice[OF this] obtain a where

   865     a: "\<forall>xa. a xa \<in> \<rat> \<and> a xa < x \<bullet> xa \<and> x \<bullet> xa - a xa < e'" ..

   866   have "\<forall>i. \<exists>y. y \<in> \<rat> \<and> x \<bullet> i < y \<and> y - x \<bullet> i < e'" (is "\<forall>i. ?th i")

   867   proof

   868     fix i

   869     from Rats_dense_in_real[of "x \<bullet> i" "x \<bullet> i + e'"] e

   870     show "?th i" by auto

   871   qed

   872   from choice[OF this] obtain b where

   873     b: "\<forall>xa. b xa \<in> \<rat> \<and> x \<bullet> xa < b xa \<and> b xa - x \<bullet> xa < e'" ..

   874   let ?a = "\<Sum>i\<in>Basis. a i *\<^sub>R i" and ?b = "\<Sum>i\<in>Basis. b i *\<^sub>R i"

   875   show ?thesis

   876   proof (rule exI[of _ ?a], rule exI[of _ ?b], safe)

   877     fix y :: 'a

   878     assume *: "y \<in> box ?a ?b"

   879     have "dist x y = sqrt (\<Sum>i\<in>Basis. (dist (x \<bullet> i) (y \<bullet> i))\<^sup>2)"

   880       unfolding setL2_def[symmetric] by (rule euclidean_dist_l2)

   881     also have "\<dots> < sqrt (\<Sum>(i::'a)\<in>Basis. e^2 / real (DIM('a)))"

   882     proof (rule real_sqrt_less_mono, rule setsum_strict_mono)

   883       fix i :: "'a"

   884       assume i: "i \<in> Basis"

   885       have "a i < y\<bullet>i \<and> y\<bullet>i < b i"

   886         using * i by (auto simp: box_def)

   887       moreover have "a i < x\<bullet>i" "x\<bullet>i - a i < e'"

   888         using a by auto

   889       moreover have "x\<bullet>i < b i" "b i - x\<bullet>i < e'"

   890         using b by auto

   891       ultimately have "\<bar>x\<bullet>i - y\<bullet>i\<bar> < 2 * e'"

   892         by auto

   893       then have "dist (x \<bullet> i) (y \<bullet> i) < e/sqrt (real (DIM('a)))"

   894         unfolding e'_def by (auto simp: dist_real_def)

   895       then have "(dist (x \<bullet> i) (y \<bullet> i))\<^sup>2 < (e/sqrt (real (DIM('a))))\<^sup>2"

   896         by (rule power_strict_mono) auto

   897       then show "(dist (x \<bullet> i) (y \<bullet> i))\<^sup>2 < e\<^sup>2 / real DIM('a)"

   898         by (simp add: power_divide)

   899     qed auto

   900     also have "\<dots> = e"

   901       using 0 < e by (simp add: real_eq_of_nat)

   902     finally show "y \<in> ball x e"

   903       by (auto simp: ball_def)

   904   qed (insert a b, auto simp: box_def)

   905 qed

   906

   907 lemma open_UNION_box:

   908   fixes M :: "'a\<Colon>euclidean_space set"

   909   assumes "open M"

   910   defines "a' \<equiv> \<lambda>f :: 'a \<Rightarrow> real \<times> real. (\<Sum>(i::'a)\<in>Basis. fst (f i) *\<^sub>R i)"

   911   defines "b' \<equiv> \<lambda>f :: 'a \<Rightarrow> real \<times> real. (\<Sum>(i::'a)\<in>Basis. snd (f i) *\<^sub>R i)"

   912   defines "I \<equiv> {f\<in>Basis \<rightarrow>\<^sub>E \<rat> \<times> \<rat>. box (a' f) (b' f) \<subseteq> M}"

   913   shows "M = (\<Union>f\<in>I. box (a' f) (b' f))"

   914 proof -

   915   {

   916     fix x assume "x \<in> M"

   917     obtain e where e: "e > 0" "ball x e \<subseteq> M"

   918       using openE[OF open M x \<in> M] by auto

   919     moreover obtain a b where ab:

   920       "x \<in> box a b"

   921       "\<forall>i \<in> Basis. a \<bullet> i \<in> \<rat>"

   922       "\<forall>i\<in>Basis. b \<bullet> i \<in> \<rat>"

   923       "box a b \<subseteq> ball x e"

   924       using rational_boxes[OF e(1)] by metis

   925     ultimately have "x \<in> (\<Union>f\<in>I. box (a' f) (b' f))"

   926        by (intro UN_I[of "\<lambda>i\<in>Basis. (a \<bullet> i, b \<bullet> i)"])

   927           (auto simp: euclidean_representation I_def a'_def b'_def)

   928   }

   929   then show ?thesis by (auto simp: I_def)

   930 qed

   931

   932 lemma box_eq_empty:

   933   fixes a :: "'a::euclidean_space"

   934   shows "(box a b = {} \<longleftrightarrow> (\<exists>i\<in>Basis. b\<bullet>i \<le> a\<bullet>i))" (is ?th1)

   935     and "(cbox a b = {} \<longleftrightarrow> (\<exists>i\<in>Basis. b\<bullet>i < a\<bullet>i))" (is ?th2)

   936 proof -

   937   {

   938     fix i x

   939     assume i: "i\<in>Basis" and as:"b\<bullet>i \<le> a\<bullet>i" and x:"x\<in>box a b"

   940     then have "a \<bullet> i < x \<bullet> i \<and> x \<bullet> i < b \<bullet> i"

   941       unfolding mem_box by (auto simp: box_def)

   942     then have "a\<bullet>i < b\<bullet>i" by auto

   943     then have False using as by auto

   944   }

   945   moreover

   946   {

   947     assume as: "\<forall>i\<in>Basis. \<not> (b\<bullet>i \<le> a\<bullet>i)"

   948     let ?x = "(1/2) *\<^sub>R (a + b)"

   949     {

   950       fix i :: 'a

   951       assume i: "i \<in> Basis"

   952       have "a\<bullet>i < b\<bullet>i"

   953         using as[THEN bspec[where x=i]] i by auto

   954       then have "a\<bullet>i < ((1/2) *\<^sub>R (a+b)) \<bullet> i" "((1/2) *\<^sub>R (a+b)) \<bullet> i < b\<bullet>i"

   955         by (auto simp: inner_add_left)

   956     }

   957     then have "box a b \<noteq> {}"

   958       using mem_box(1)[of "?x" a b] by auto

   959   }

   960   ultimately show ?th1 by blast

   961

   962   {

   963     fix i x

   964     assume i: "i \<in> Basis" and as:"b\<bullet>i < a\<bullet>i" and x:"x\<in>cbox a b"

   965     then have "a \<bullet> i \<le> x \<bullet> i \<and> x \<bullet> i \<le> b \<bullet> i"

   966       unfolding mem_box by auto

   967     then have "a\<bullet>i \<le> b\<bullet>i" by auto

   968     then have False using as by auto

   969   }

   970   moreover

   971   {

   972     assume as:"\<forall>i\<in>Basis. \<not> (b\<bullet>i < a\<bullet>i)"

   973     let ?x = "(1/2) *\<^sub>R (a + b)"

   974     {

   975       fix i :: 'a

   976       assume i:"i \<in> Basis"

   977       have "a\<bullet>i \<le> b\<bullet>i"

   978         using as[THEN bspec[where x=i]] i by auto

   979       then have "a\<bullet>i \<le> ((1/2) *\<^sub>R (a+b)) \<bullet> i" "((1/2) *\<^sub>R (a+b)) \<bullet> i \<le> b\<bullet>i"

   980         by (auto simp: inner_add_left)

   981     }

   982     then have "cbox a b \<noteq> {}"

   983       using mem_box(2)[of "?x" a b] by auto

   984   }

   985   ultimately show ?th2 by blast

   986 qed

   987

   988 lemma box_ne_empty:

   989   fixes a :: "'a::euclidean_space"

   990   shows "cbox a b \<noteq> {} \<longleftrightarrow> (\<forall>i\<in>Basis. a\<bullet>i \<le> b\<bullet>i)"

   991   and "box a b \<noteq> {} \<longleftrightarrow> (\<forall>i\<in>Basis. a\<bullet>i < b\<bullet>i)"

   992   unfolding box_eq_empty[of a b] by fastforce+

   993

   994 lemma

   995   fixes a :: "'a::euclidean_space"

   996   shows cbox_sing: "cbox a a = {a}"

   997     and box_sing: "box a a = {}"

   998   unfolding set_eq_iff mem_box eq_iff [symmetric]

   999   by (auto intro!: euclidean_eqI[where 'a='a])

  1000      (metis all_not_in_conv nonempty_Basis)

  1001

  1002 lemma subset_box_imp:

  1003   fixes a :: "'a::euclidean_space"

  1004   shows "(\<forall>i\<in>Basis. a\<bullet>i \<le> c\<bullet>i \<and> d\<bullet>i \<le> b\<bullet>i) \<Longrightarrow> cbox c d \<subseteq> cbox a b"

  1005     and "(\<forall>i\<in>Basis. a\<bullet>i < c\<bullet>i \<and> d\<bullet>i < b\<bullet>i) \<Longrightarrow> cbox c d \<subseteq> box a b"

  1006     and "(\<forall>i\<in>Basis. a\<bullet>i \<le> c\<bullet>i \<and> d\<bullet>i \<le> b\<bullet>i) \<Longrightarrow> box c d \<subseteq> cbox a b"

  1007      and "(\<forall>i\<in>Basis. a\<bullet>i \<le> c\<bullet>i \<and> d\<bullet>i \<le> b\<bullet>i) \<Longrightarrow> box c d \<subseteq> box a b"

  1008   unfolding subset_eq[unfolded Ball_def] unfolding mem_box

  1009    by (best intro: order_trans less_le_trans le_less_trans less_imp_le)+

  1010

  1011 lemma box_subset_cbox:

  1012   fixes a :: "'a::euclidean_space"

  1013   shows "box a b \<subseteq> cbox a b"

  1014   unfolding subset_eq [unfolded Ball_def] mem_box

  1015   by (fast intro: less_imp_le)

  1016

  1017 lemma subset_box:

  1018   fixes a :: "'a::euclidean_space"

  1019   shows "cbox c d \<subseteq> cbox a b \<longleftrightarrow> (\<forall>i\<in>Basis. c\<bullet>i \<le> d\<bullet>i) --> (\<forall>i\<in>Basis. a\<bullet>i \<le> c\<bullet>i \<and> d\<bullet>i \<le> b\<bullet>i)" (is ?th1)

  1020     and "cbox c d \<subseteq> box a b \<longleftrightarrow> (\<forall>i\<in>Basis. c\<bullet>i \<le> d\<bullet>i) --> (\<forall>i\<in>Basis. a\<bullet>i < c\<bullet>i \<and> d\<bullet>i < b\<bullet>i)" (is ?th2)

  1021     and "box c d \<subseteq> cbox a b \<longleftrightarrow> (\<forall>i\<in>Basis. c\<bullet>i < d\<bullet>i) --> (\<forall>i\<in>Basis. a\<bullet>i \<le> c\<bullet>i \<and> d\<bullet>i \<le> b\<bullet>i)" (is ?th3)

  1022     and "box c d \<subseteq> box a b \<longleftrightarrow> (\<forall>i\<in>Basis. c\<bullet>i < d\<bullet>i) --> (\<forall>i\<in>Basis. a\<bullet>i \<le> c\<bullet>i \<and> d\<bullet>i \<le> b\<bullet>i)" (is ?th4)

  1023 proof -

  1024   show ?th1

  1025     unfolding subset_eq and Ball_def and mem_box

  1026     by (auto intro: order_trans)

  1027   show ?th2

  1028     unfolding subset_eq and Ball_def and mem_box

  1029     by (auto intro: le_less_trans less_le_trans order_trans less_imp_le)

  1030   {

  1031     assume as: "box c d \<subseteq> cbox a b" "\<forall>i\<in>Basis. c\<bullet>i < d\<bullet>i"

  1032     then have "box c d \<noteq> {}"

  1033       unfolding box_eq_empty by auto

  1034     fix i :: 'a

  1035     assume i: "i \<in> Basis"

  1036     (** TODO combine the following two parts as done in the HOL_light version. **)

  1037     {

  1038       let ?x = "(\<Sum>j\<in>Basis. (if j=i then ((min (a\<bullet>j) (d\<bullet>j))+c\<bullet>j)/2 else (c\<bullet>j+d\<bullet>j)/2) *\<^sub>R j)::'a"

  1039       assume as2: "a\<bullet>i > c\<bullet>i"

  1040       {

  1041         fix j :: 'a

  1042         assume j: "j \<in> Basis"

  1043         then have "c \<bullet> j < ?x \<bullet> j \<and> ?x \<bullet> j < d \<bullet> j"

  1044           apply (cases "j = i")

  1045           using as(2)[THEN bspec[where x=j]] i

  1046           apply (auto simp add: as2)

  1047           done

  1048       }

  1049       then have "?x\<in>box c d"

  1050         using i unfolding mem_box by auto

  1051       moreover

  1052       have "?x \<notin> cbox a b"

  1053         unfolding mem_box

  1054         apply auto

  1055         apply (rule_tac x=i in bexI)

  1056         using as(2)[THEN bspec[where x=i]] and as2 i

  1057         apply auto

  1058         done

  1059       ultimately have False using as by auto

  1060     }

  1061     then have "a\<bullet>i \<le> c\<bullet>i" by (rule ccontr) auto

  1062     moreover

  1063     {

  1064       let ?x = "(\<Sum>j\<in>Basis. (if j=i then ((max (b\<bullet>j) (c\<bullet>j))+d\<bullet>j)/2 else (c\<bullet>j+d\<bullet>j)/2) *\<^sub>R j)::'a"

  1065       assume as2: "b\<bullet>i < d\<bullet>i"

  1066       {

  1067         fix j :: 'a

  1068         assume "j\<in>Basis"

  1069         then have "d \<bullet> j > ?x \<bullet> j \<and> ?x \<bullet> j > c \<bullet> j"

  1070           apply (cases "j = i")

  1071           using as(2)[THEN bspec[where x=j]]

  1072           apply (auto simp add: as2)

  1073           done

  1074       }

  1075       then have "?x\<in>box c d"

  1076         unfolding mem_box by auto

  1077       moreover

  1078       have "?x\<notin>cbox a b"

  1079         unfolding mem_box

  1080         apply auto

  1081         apply (rule_tac x=i in bexI)

  1082         using as(2)[THEN bspec[where x=i]] and as2 using i

  1083         apply auto

  1084         done

  1085       ultimately have False using as by auto

  1086     }

  1087     then have "b\<bullet>i \<ge> d\<bullet>i" by (rule ccontr) auto

  1088     ultimately

  1089     have "a\<bullet>i \<le> c\<bullet>i \<and> d\<bullet>i \<le> b\<bullet>i" by auto

  1090   } note part1 = this

  1091   show ?th3

  1092     unfolding subset_eq and Ball_def and mem_box

  1093     apply (rule, rule, rule, rule)

  1094     apply (rule part1)

  1095     unfolding subset_eq and Ball_def and mem_box

  1096     prefer 4

  1097     apply auto

  1098     apply (erule_tac x=xa in allE, erule_tac x=xa in allE, fastforce)+

  1099     done

  1100   {

  1101     assume as: "box c d \<subseteq> box a b" "\<forall>i\<in>Basis. c\<bullet>i < d\<bullet>i"

  1102     fix i :: 'a

  1103     assume i:"i\<in>Basis"

  1104     from as(1) have "box c d \<subseteq> cbox a b"

  1105       using box_subset_cbox[of a b] by auto

  1106     then have "a\<bullet>i \<le> c\<bullet>i \<and> d\<bullet>i \<le> b\<bullet>i"

  1107       using part1 and as(2) using i by auto

  1108   } note * = this

  1109   show ?th4

  1110     unfolding subset_eq and Ball_def and mem_box

  1111     apply (rule, rule, rule, rule)

  1112     apply (rule *)

  1113     unfolding subset_eq and Ball_def and mem_box

  1114     prefer 4

  1115     apply auto

  1116     apply (erule_tac x=xa in allE, simp)+

  1117     done

  1118 qed

  1119

  1120 lemma inter_interval:

  1121   fixes a :: "'a::euclidean_space"

  1122   shows "cbox a b \<inter> cbox c d =

  1123     cbox (\<Sum>i\<in>Basis. max (a\<bullet>i) (c\<bullet>i) *\<^sub>R i) (\<Sum>i\<in>Basis. min (b\<bullet>i) (d\<bullet>i) *\<^sub>R i)"

  1124   unfolding set_eq_iff and Int_iff and mem_box

  1125   by auto

  1126

  1127 lemma disjoint_interval:

  1128   fixes a::"'a::euclidean_space"

  1129   shows "cbox a b \<inter> cbox c d = {} \<longleftrightarrow> (\<exists>i\<in>Basis. (b\<bullet>i < a\<bullet>i \<or> d\<bullet>i < c\<bullet>i \<or> b\<bullet>i < c\<bullet>i \<or> d\<bullet>i < a\<bullet>i))" (is ?th1)

  1130     and "cbox a b \<inter> box c d = {} \<longleftrightarrow> (\<exists>i\<in>Basis. (b\<bullet>i < a\<bullet>i \<or> d\<bullet>i \<le> c\<bullet>i \<or> b\<bullet>i \<le> c\<bullet>i \<or> d\<bullet>i \<le> a\<bullet>i))" (is ?th2)

  1131     and "box a b \<inter> cbox c d = {} \<longleftrightarrow> (\<exists>i\<in>Basis. (b\<bullet>i \<le> a\<bullet>i \<or> d\<bullet>i < c\<bullet>i \<or> b\<bullet>i \<le> c\<bullet>i \<or> d\<bullet>i \<le> a\<bullet>i))" (is ?th3)

  1132     and "box a b \<inter> box c d = {} \<longleftrightarrow> (\<exists>i\<in>Basis. (b\<bullet>i \<le> a\<bullet>i \<or> d\<bullet>i \<le> c\<bullet>i \<or> b\<bullet>i \<le> c\<bullet>i \<or> d\<bullet>i \<le> a\<bullet>i))" (is ?th4)

  1133 proof -

  1134   let ?z = "(\<Sum>i\<in>Basis. (((max (a\<bullet>i) (c\<bullet>i)) + (min (b\<bullet>i) (d\<bullet>i))) / 2) *\<^sub>R i)::'a"

  1135   have **: "\<And>P Q. (\<And>i :: 'a. i \<in> Basis \<Longrightarrow> Q ?z i \<Longrightarrow> P i) \<Longrightarrow>

  1136       (\<And>i x :: 'a. i \<in> Basis \<Longrightarrow> P i \<Longrightarrow> Q x i) \<Longrightarrow> (\<forall>x. \<exists>i\<in>Basis. Q x i) \<longleftrightarrow> (\<exists>i\<in>Basis. P i)"

  1137     by blast

  1138   note * = set_eq_iff Int_iff empty_iff mem_box ball_conj_distrib[symmetric] eq_False ball_simps(10)

  1139   show ?th1 unfolding * by (intro **) auto

  1140   show ?th2 unfolding * by (intro **) auto

  1141   show ?th3 unfolding * by (intro **) auto

  1142   show ?th4 unfolding * by (intro **) auto

  1143 qed

  1144

  1145 text {* Intervals in general, including infinite and mixtures of open and closed. *}

  1146

  1147 definition "is_interval (s::('a::euclidean_space) set) \<longleftrightarrow>

  1148   (\<forall>a\<in>s. \<forall>b\<in>s. \<forall>x. (\<forall>i\<in>Basis. ((a\<bullet>i \<le> x\<bullet>i \<and> x\<bullet>i \<le> b\<bullet>i) \<or> (b\<bullet>i \<le> x\<bullet>i \<and> x\<bullet>i \<le> a\<bullet>i))) \<longrightarrow> x \<in> s)"

  1149

  1150 lemma is_interval_cbox: "is_interval (cbox a (b::'a::euclidean_space))" (is ?th1)

  1151   and is_interval_box: "is_interval (box a b)" (is ?th2)

  1152   unfolding is_interval_def mem_box Ball_def atLeastAtMost_iff

  1153   by (meson order_trans le_less_trans less_le_trans less_trans)+

  1154

  1155 lemma is_interval_empty:

  1156  "is_interval {}"

  1157   unfolding is_interval_def

  1158   by simp

  1159

  1160 lemma is_interval_univ:

  1161  "is_interval UNIV"

  1162   unfolding is_interval_def

  1163   by simp

  1164

  1165 lemma mem_is_intervalI:

  1166   assumes "is_interval s"

  1167   assumes "a \<in> s" "b \<in> s"

  1168   assumes "\<And>i. i \<in> Basis \<Longrightarrow> a \<bullet> i \<le> x \<bullet> i \<and> x \<bullet> i \<le> b \<bullet> i \<or> b \<bullet> i \<le> x \<bullet> i \<and> x \<bullet> i \<le> a \<bullet> i"

  1169   shows "x \<in> s"

  1170   by (rule assms(1)[simplified is_interval_def, rule_format, OF assms(2,3,4)])

  1171

  1172 lemma interval_subst:

  1173   fixes S::"'a::euclidean_space set"

  1174   assumes "is_interval S"

  1175   assumes "x \<in> S" "y j \<in> S"

  1176   assumes "j \<in> Basis"

  1177   shows "(\<Sum>i\<in>Basis. (if i = j then y i \<bullet> i else x \<bullet> i) *\<^sub>R i) \<in> S"

  1178   by (rule mem_is_intervalI[OF assms(1,2)]) (auto simp: assms)

  1179

  1180 lemma mem_box_componentwiseI:

  1181   fixes S::"'a::euclidean_space set"

  1182   assumes "is_interval S"

  1183   assumes "\<And>i. i \<in> Basis \<Longrightarrow> x \<bullet> i \<in> ((\<lambda>x. x \<bullet> i)  S)"

  1184   shows "x \<in> S"

  1185 proof -

  1186   from assms have "\<forall>i \<in> Basis. \<exists>s \<in> S. x \<bullet> i = s \<bullet> i"

  1187     by auto

  1188   with finite_Basis obtain s and bs::"'a list" where

  1189     s: "\<And>i. i \<in> Basis \<Longrightarrow> x \<bullet> i = s i \<bullet> i" "\<And>i. i \<in> Basis \<Longrightarrow> s i \<in> S" and

  1190     bs: "set bs = Basis" "distinct bs"

  1191     by (metis finite_distinct_list)

  1192   from nonempty_Basis s obtain j where j: "j \<in> Basis" "s j \<in> S" by blast

  1193   def y \<equiv> "rec_list

  1194     (s j)

  1195     (\<lambda>j _ Y. (\<Sum>i\<in>Basis. (if i = j then s i \<bullet> i else Y \<bullet> i) *\<^sub>R i))"

  1196   have "x = (\<Sum>i\<in>Basis. (if i \<in> set bs then s i \<bullet> i else s j \<bullet> i) *\<^sub>R i)"

  1197     using bs by (auto simp add: s(1)[symmetric] euclidean_representation)

  1198   also have [symmetric]: "y bs = \<dots>"

  1199     using bs(2) bs(1)[THEN equalityD1]

  1200     by (induct bs) (auto simp: y_def euclidean_representation intro!: euclidean_eqI[where 'a='a])

  1201   also have "y bs \<in> S"

  1202     using bs(1)[THEN equalityD1]

  1203     apply (induct bs)

  1204     apply (auto simp: y_def j)

  1205     apply (rule interval_subst[OF assms(1)])

  1206     apply (auto simp: s)

  1207     done

  1208   finally show ?thesis .

  1209 qed

  1210

  1211

  1212 subsection{* Connectedness *}

  1213

  1214 lemma connected_local:

  1215  "connected S \<longleftrightarrow>

  1216   \<not> (\<exists>e1 e2.

  1217       openin (subtopology euclidean S) e1 \<and>

  1218       openin (subtopology euclidean S) e2 \<and>

  1219       S \<subseteq> e1 \<union> e2 \<and>

  1220       e1 \<inter> e2 = {} \<and>

  1221       e1 \<noteq> {} \<and>

  1222       e2 \<noteq> {})"

  1223   unfolding connected_def openin_open

  1224   by blast

  1225

  1226 lemma exists_diff:

  1227   fixes P :: "'a set \<Rightarrow> bool"

  1228   shows "(\<exists>S. P(- S)) \<longleftrightarrow> (\<exists>S. P S)" (is "?lhs \<longleftrightarrow> ?rhs")

  1229 proof -

  1230   {

  1231     assume "?lhs"

  1232     then have ?rhs by blast

  1233   }

  1234   moreover

  1235   {

  1236     fix S

  1237     assume H: "P S"

  1238     have "S = - (- S)" by auto

  1239     with H have "P (- (- S))" by metis

  1240   }

  1241   ultimately show ?thesis by metis

  1242 qed

  1243

  1244 lemma connected_clopen: "connected S \<longleftrightarrow>

  1245   (\<forall>T. openin (subtopology euclidean S) T \<and>

  1246      closedin (subtopology euclidean S) T \<longrightarrow> T = {} \<or> T = S)" (is "?lhs \<longleftrightarrow> ?rhs")

  1247 proof -

  1248   have "\<not> connected S \<longleftrightarrow>

  1249     (\<exists>e1 e2. open e1 \<and> open (- e2) \<and> S \<subseteq> e1 \<union> (- e2) \<and> e1 \<inter> (- e2) \<inter> S = {} \<and> e1 \<inter> S \<noteq> {} \<and> (- e2) \<inter> S \<noteq> {})"

  1250     unfolding connected_def openin_open closedin_closed

  1251     by (metis double_complement)

  1252   then have th0: "connected S \<longleftrightarrow>

  1253     \<not> (\<exists>e2 e1. closed e2 \<and> open e1 \<and> S \<subseteq> e1 \<union> (- e2) \<and> e1 \<inter> (- e2) \<inter> S = {} \<and> e1 \<inter> S \<noteq> {} \<and> (- e2) \<inter> S \<noteq> {})"

  1254     (is " _ \<longleftrightarrow> \<not> (\<exists>e2 e1. ?P e2 e1)")

  1255     apply (simp add: closed_def)

  1256     apply metis

  1257     done

  1258   have th1: "?rhs \<longleftrightarrow> \<not> (\<exists>t' t. closed t'\<and>t = S\<inter>t' \<and> t\<noteq>{} \<and> t\<noteq>S \<and> (\<exists>t'. open t' \<and> t = S \<inter> t'))"

  1259     (is "_ \<longleftrightarrow> \<not> (\<exists>t' t. ?Q t' t)")

  1260     unfolding connected_def openin_open closedin_closed by auto

  1261   {

  1262     fix e2

  1263     {

  1264       fix e1

  1265       have "?P e2 e1 \<longleftrightarrow> (\<exists>t. closed e2 \<and> t = S\<inter>e2 \<and> open e1 \<and> t = S\<inter>e1 \<and> t\<noteq>{} \<and> t \<noteq> S)"

  1266         by auto

  1267     }

  1268     then have "(\<exists>e1. ?P e2 e1) \<longleftrightarrow> (\<exists>t. ?Q e2 t)"

  1269       by metis

  1270   }

  1271   then have "\<forall>e2. (\<exists>e1. ?P e2 e1) \<longleftrightarrow> (\<exists>t. ?Q e2 t)"

  1272     by blast

  1273   then show ?thesis

  1274     unfolding th0 th1 by simp

  1275 qed

  1276

  1277

  1278 subsection{* Limit points *}

  1279

  1280 definition (in topological_space) islimpt:: "'a \<Rightarrow> 'a set \<Rightarrow> bool"  (infixr "islimpt" 60)

  1281   where "x islimpt S \<longleftrightarrow> (\<forall>T. x\<in>T \<longrightarrow> open T \<longrightarrow> (\<exists>y\<in>S. y\<in>T \<and> y\<noteq>x))"

  1282

  1283 lemma islimptI:

  1284   assumes "\<And>T. x \<in> T \<Longrightarrow> open T \<Longrightarrow> \<exists>y\<in>S. y \<in> T \<and> y \<noteq> x"

  1285   shows "x islimpt S"

  1286   using assms unfolding islimpt_def by auto

  1287

  1288 lemma islimptE:

  1289   assumes "x islimpt S" and "x \<in> T" and "open T"

  1290   obtains y where "y \<in> S" and "y \<in> T" and "y \<noteq> x"

  1291   using assms unfolding islimpt_def by auto

  1292

  1293 lemma islimpt_iff_eventually: "x islimpt S \<longleftrightarrow> \<not> eventually (\<lambda>y. y \<notin> S) (at x)"

  1294   unfolding islimpt_def eventually_at_topological by auto

  1295

  1296 lemma islimpt_subset: "x islimpt S \<Longrightarrow> S \<subseteq> T \<Longrightarrow> x islimpt T"

  1297   unfolding islimpt_def by fast

  1298

  1299 lemma islimpt_approachable:

  1300   fixes x :: "'a::metric_space"

  1301   shows "x islimpt S \<longleftrightarrow> (\<forall>e>0. \<exists>x'\<in>S. x' \<noteq> x \<and> dist x' x < e)"

  1302   unfolding islimpt_iff_eventually eventually_at by fast

  1303

  1304 lemma islimpt_approachable_le:

  1305   fixes x :: "'a::metric_space"

  1306   shows "x islimpt S \<longleftrightarrow> (\<forall>e>0. \<exists>x'\<in> S. x' \<noteq> x \<and> dist x' x \<le> e)"

  1307   unfolding islimpt_approachable

  1308   using approachable_lt_le [where f="\<lambda>y. dist y x" and P="\<lambda>y. y \<notin> S \<or> y = x",

  1309     THEN arg_cong [where f=Not]]

  1310   by (simp add: Bex_def conj_commute conj_left_commute)

  1311

  1312 lemma islimpt_UNIV_iff: "x islimpt UNIV \<longleftrightarrow> \<not> open {x}"

  1313   unfolding islimpt_def by (safe, fast, case_tac "T = {x}", fast, fast)

  1314

  1315 lemma islimpt_punctured: "x islimpt S = x islimpt (S-{x})"

  1316   unfolding islimpt_def by blast

  1317

  1318 text {* A perfect space has no isolated points. *}

  1319

  1320 lemma islimpt_UNIV [simp, intro]: "(x::'a::perfect_space) islimpt UNIV"

  1321   unfolding islimpt_UNIV_iff by (rule not_open_singleton)

  1322

  1323 lemma perfect_choose_dist:

  1324   fixes x :: "'a::{perfect_space, metric_space}"

  1325   shows "0 < r \<Longrightarrow> \<exists>a. a \<noteq> x \<and> dist a x < r"

  1326   using islimpt_UNIV [of x]

  1327   by (simp add: islimpt_approachable)

  1328

  1329 lemma closed_limpt: "closed S \<longleftrightarrow> (\<forall>x. x islimpt S \<longrightarrow> x \<in> S)"

  1330   unfolding closed_def

  1331   apply (subst open_subopen)

  1332   apply (simp add: islimpt_def subset_eq)

  1333   apply (metis ComplE ComplI)

  1334   done

  1335

  1336 lemma islimpt_EMPTY[simp]: "\<not> x islimpt {}"

  1337   unfolding islimpt_def by auto

  1338

  1339 lemma finite_set_avoid:

  1340   fixes a :: "'a::metric_space"

  1341   assumes fS: "finite S"

  1342   shows  "\<exists>d>0. \<forall>x\<in>S. x \<noteq> a \<longrightarrow> d \<le> dist a x"

  1343 proof (induct rule: finite_induct[OF fS])

  1344   case 1

  1345   then show ?case by (auto intro: zero_less_one)

  1346 next

  1347   case (2 x F)

  1348   from 2 obtain d where d: "d >0" "\<forall>x\<in>F. x\<noteq>a \<longrightarrow> d \<le> dist a x"

  1349     by blast

  1350   show ?case

  1351   proof (cases "x = a")

  1352     case True

  1353     then show ?thesis using d by auto

  1354   next

  1355     case False

  1356     let ?d = "min d (dist a x)"

  1357     have dp: "?d > 0"

  1358       using False d(1) using dist_nz by auto

  1359     from d have d': "\<forall>x\<in>F. x\<noteq>a \<longrightarrow> ?d \<le> dist a x"

  1360       by auto

  1361     with dp False show ?thesis

  1362       by (auto intro!: exI[where x="?d"])

  1363   qed

  1364 qed

  1365

  1366 lemma islimpt_Un: "x islimpt (S \<union> T) \<longleftrightarrow> x islimpt S \<or> x islimpt T"

  1367   by (simp add: islimpt_iff_eventually eventually_conj_iff)

  1368

  1369 lemma discrete_imp_closed:

  1370   fixes S :: "'a::metric_space set"

  1371   assumes e: "0 < e"

  1372     and d: "\<forall>x \<in> S. \<forall>y \<in> S. dist y x < e \<longrightarrow> y = x"

  1373   shows "closed S"

  1374 proof -

  1375   {

  1376     fix x

  1377     assume C: "\<forall>e>0. \<exists>x'\<in>S. x' \<noteq> x \<and> dist x' x < e"

  1378     from e have e2: "e/2 > 0" by arith

  1379     from C[rule_format, OF e2] obtain y where y: "y \<in> S" "y \<noteq> x" "dist y x < e/2"

  1380       by blast

  1381     let ?m = "min (e/2) (dist x y) "

  1382     from e2 y(2) have mp: "?m > 0"

  1383       by (simp add: dist_nz[symmetric])

  1384     from C[rule_format, OF mp] obtain z where z: "z \<in> S" "z \<noteq> x" "dist z x < ?m"

  1385       by blast

  1386     have th: "dist z y < e" using z y

  1387       by (intro dist_triangle_lt [where z=x], simp)

  1388     from d[rule_format, OF y(1) z(1) th] y z

  1389     have False by (auto simp add: dist_commute)}

  1390   then show ?thesis

  1391     by (metis islimpt_approachable closed_limpt [where 'a='a])

  1392 qed

  1393

  1394

  1395 subsection {* Interior of a Set *}

  1396

  1397 definition "interior S = \<Union>{T. open T \<and> T \<subseteq> S}"

  1398

  1399 lemma interiorI [intro?]:

  1400   assumes "open T" and "x \<in> T" and "T \<subseteq> S"

  1401   shows "x \<in> interior S"

  1402   using assms unfolding interior_def by fast

  1403

  1404 lemma interiorE [elim?]:

  1405   assumes "x \<in> interior S"

  1406   obtains T where "open T" and "x \<in> T" and "T \<subseteq> S"

  1407   using assms unfolding interior_def by fast

  1408

  1409 lemma open_interior [simp, intro]: "open (interior S)"

  1410   by (simp add: interior_def open_Union)

  1411

  1412 lemma interior_subset: "interior S \<subseteq> S"

  1413   by (auto simp add: interior_def)

  1414

  1415 lemma interior_maximal: "T \<subseteq> S \<Longrightarrow> open T \<Longrightarrow> T \<subseteq> interior S"

  1416   by (auto simp add: interior_def)

  1417

  1418 lemma interior_open: "open S \<Longrightarrow> interior S = S"

  1419   by (intro equalityI interior_subset interior_maximal subset_refl)

  1420

  1421 lemma interior_eq: "interior S = S \<longleftrightarrow> open S"

  1422   by (metis open_interior interior_open)

  1423

  1424 lemma open_subset_interior: "open S \<Longrightarrow> S \<subseteq> interior T \<longleftrightarrow> S \<subseteq> T"

  1425   by (metis interior_maximal interior_subset subset_trans)

  1426

  1427 lemma interior_empty [simp]: "interior {} = {}"

  1428   using open_empty by (rule interior_open)

  1429

  1430 lemma interior_UNIV [simp]: "interior UNIV = UNIV"

  1431   using open_UNIV by (rule interior_open)

  1432

  1433 lemma interior_interior [simp]: "interior (interior S) = interior S"

  1434   using open_interior by (rule interior_open)

  1435

  1436 lemma interior_mono: "S \<subseteq> T \<Longrightarrow> interior S \<subseteq> interior T"

  1437   by (auto simp add: interior_def)

  1438

  1439 lemma interior_unique:

  1440   assumes "T \<subseteq> S" and "open T"

  1441   assumes "\<And>T'. T' \<subseteq> S \<Longrightarrow> open T' \<Longrightarrow> T' \<subseteq> T"

  1442   shows "interior S = T"

  1443   by (intro equalityI assms interior_subset open_interior interior_maximal)

  1444

  1445 lemma interior_inter [simp]: "interior (S \<inter> T) = interior S \<inter> interior T"

  1446   by (intro equalityI Int_mono Int_greatest interior_mono Int_lower1

  1447     Int_lower2 interior_maximal interior_subset open_Int open_interior)

  1448

  1449 lemma mem_interior: "x \<in> interior S \<longleftrightarrow> (\<exists>e>0. ball x e \<subseteq> S)"

  1450   using open_contains_ball_eq [where S="interior S"]

  1451   by (simp add: open_subset_interior)

  1452

  1453 lemma interior_limit_point [intro]:

  1454   fixes x :: "'a::perfect_space"

  1455   assumes x: "x \<in> interior S"

  1456   shows "x islimpt S"

  1457   using x islimpt_UNIV [of x]

  1458   unfolding interior_def islimpt_def

  1459   apply (clarsimp, rename_tac T T')

  1460   apply (drule_tac x="T \<inter> T'" in spec)

  1461   apply (auto simp add: open_Int)

  1462   done

  1463

  1464 lemma interior_closed_Un_empty_interior:

  1465   assumes cS: "closed S"

  1466     and iT: "interior T = {}"

  1467   shows "interior (S \<union> T) = interior S"

  1468 proof

  1469   show "interior S \<subseteq> interior (S \<union> T)"

  1470     by (rule interior_mono) (rule Un_upper1)

  1471   show "interior (S \<union> T) \<subseteq> interior S"

  1472   proof

  1473     fix x

  1474     assume "x \<in> interior (S \<union> T)"

  1475     then obtain R where "open R" "x \<in> R" "R \<subseteq> S \<union> T" ..

  1476     show "x \<in> interior S"

  1477     proof (rule ccontr)

  1478       assume "x \<notin> interior S"

  1479       with x \<in> R open R obtain y where "y \<in> R - S"

  1480         unfolding interior_def by fast

  1481       from open R closed S have "open (R - S)"

  1482         by (rule open_Diff)

  1483       from R \<subseteq> S \<union> T have "R - S \<subseteq> T"

  1484         by fast

  1485       from y \<in> R - S open (R - S) R - S \<subseteq> T interior T = {} show False

  1486         unfolding interior_def by fast

  1487     qed

  1488   qed

  1489 qed

  1490

  1491 lemma interior_Times: "interior (A \<times> B) = interior A \<times> interior B"

  1492 proof (rule interior_unique)

  1493   show "interior A \<times> interior B \<subseteq> A \<times> B"

  1494     by (intro Sigma_mono interior_subset)

  1495   show "open (interior A \<times> interior B)"

  1496     by (intro open_Times open_interior)

  1497   fix T

  1498   assume "T \<subseteq> A \<times> B" and "open T"

  1499   then show "T \<subseteq> interior A \<times> interior B"

  1500   proof safe

  1501     fix x y

  1502     assume "(x, y) \<in> T"

  1503     then obtain C D where "open C" "open D" "C \<times> D \<subseteq> T" "x \<in> C" "y \<in> D"

  1504       using open T unfolding open_prod_def by fast

  1505     then have "open C" "open D" "C \<subseteq> A" "D \<subseteq> B" "x \<in> C" "y \<in> D"

  1506       using T \<subseteq> A \<times> B by auto

  1507     then show "x \<in> interior A" and "y \<in> interior B"

  1508       by (auto intro: interiorI)

  1509   qed

  1510 qed

  1511

  1512

  1513 subsection {* Closure of a Set *}

  1514

  1515 definition "closure S = S \<union> {x | x. x islimpt S}"

  1516

  1517 lemma interior_closure: "interior S = - (closure (- S))"

  1518   unfolding interior_def closure_def islimpt_def by auto

  1519

  1520 lemma closure_interior: "closure S = - interior (- S)"

  1521   unfolding interior_closure by simp

  1522

  1523 lemma closed_closure[simp, intro]: "closed (closure S)"

  1524   unfolding closure_interior by (simp add: closed_Compl)

  1525

  1526 lemma closure_subset: "S \<subseteq> closure S"

  1527   unfolding closure_def by simp

  1528

  1529 lemma closure_hull: "closure S = closed hull S"

  1530   unfolding hull_def closure_interior interior_def by auto

  1531

  1532 lemma closure_eq: "closure S = S \<longleftrightarrow> closed S"

  1533   unfolding closure_hull using closed_Inter by (rule hull_eq)

  1534

  1535 lemma closure_closed [simp]: "closed S \<Longrightarrow> closure S = S"

  1536   unfolding closure_eq .

  1537

  1538 lemma closure_closure [simp]: "closure (closure S) = closure S"

  1539   unfolding closure_hull by (rule hull_hull)

  1540

  1541 lemma closure_mono: "S \<subseteq> T \<Longrightarrow> closure S \<subseteq> closure T"

  1542   unfolding closure_hull by (rule hull_mono)

  1543

  1544 lemma closure_minimal: "S \<subseteq> T \<Longrightarrow> closed T \<Longrightarrow> closure S \<subseteq> T"

  1545   unfolding closure_hull by (rule hull_minimal)

  1546

  1547 lemma closure_unique:

  1548   assumes "S \<subseteq> T"

  1549     and "closed T"

  1550     and "\<And>T'. S \<subseteq> T' \<Longrightarrow> closed T' \<Longrightarrow> T \<subseteq> T'"

  1551   shows "closure S = T"

  1552   using assms unfolding closure_hull by (rule hull_unique)

  1553

  1554 lemma closure_empty [simp]: "closure {} = {}"

  1555   using closed_empty by (rule closure_closed)

  1556

  1557 lemma closure_UNIV [simp]: "closure UNIV = UNIV"

  1558   using closed_UNIV by (rule closure_closed)

  1559

  1560 lemma closure_union [simp]: "closure (S \<union> T) = closure S \<union> closure T"

  1561   unfolding closure_interior by simp

  1562

  1563 lemma closure_eq_empty: "closure S = {} \<longleftrightarrow> S = {}"

  1564   using closure_empty closure_subset[of S]

  1565   by blast

  1566

  1567 lemma closure_subset_eq: "closure S \<subseteq> S \<longleftrightarrow> closed S"

  1568   using closure_eq[of S] closure_subset[of S]

  1569   by simp

  1570

  1571 lemma open_inter_closure_eq_empty:

  1572   "open S \<Longrightarrow> (S \<inter> closure T) = {} \<longleftrightarrow> S \<inter> T = {}"

  1573   using open_subset_interior[of S "- T"]

  1574   using interior_subset[of "- T"]

  1575   unfolding closure_interior

  1576   by auto

  1577

  1578 lemma open_inter_closure_subset:

  1579   "open S \<Longrightarrow> (S \<inter> (closure T)) \<subseteq> closure(S \<inter> T)"

  1580 proof

  1581   fix x

  1582   assume as: "open S" "x \<in> S \<inter> closure T"

  1583   {

  1584     assume *: "x islimpt T"

  1585     have "x islimpt (S \<inter> T)"

  1586     proof (rule islimptI)

  1587       fix A

  1588       assume "x \<in> A" "open A"

  1589       with as have "x \<in> A \<inter> S" "open (A \<inter> S)"

  1590         by (simp_all add: open_Int)

  1591       with * obtain y where "y \<in> T" "y \<in> A \<inter> S" "y \<noteq> x"

  1592         by (rule islimptE)

  1593       then have "y \<in> S \<inter> T" "y \<in> A \<and> y \<noteq> x"

  1594         by simp_all

  1595       then show "\<exists>y\<in>(S \<inter> T). y \<in> A \<and> y \<noteq> x" ..

  1596     qed

  1597   }

  1598   then show "x \<in> closure (S \<inter> T)" using as

  1599     unfolding closure_def

  1600     by blast

  1601 qed

  1602

  1603 lemma closure_complement: "closure (- S) = - interior S"

  1604   unfolding closure_interior by simp

  1605

  1606 lemma interior_complement: "interior (- S) = - closure S"

  1607   unfolding closure_interior by simp

  1608

  1609 lemma closure_Times: "closure (A \<times> B) = closure A \<times> closure B"

  1610 proof (rule closure_unique)

  1611   show "A \<times> B \<subseteq> closure A \<times> closure B"

  1612     by (intro Sigma_mono closure_subset)

  1613   show "closed (closure A \<times> closure B)"

  1614     by (intro closed_Times closed_closure)

  1615   fix T

  1616   assume "A \<times> B \<subseteq> T" and "closed T"

  1617   then show "closure A \<times> closure B \<subseteq> T"

  1618     apply (simp add: closed_def open_prod_def, clarify)

  1619     apply (rule ccontr)

  1620     apply (drule_tac x="(a, b)" in bspec, simp, clarify, rename_tac C D)

  1621     apply (simp add: closure_interior interior_def)

  1622     apply (drule_tac x=C in spec)

  1623     apply (drule_tac x=D in spec)

  1624     apply auto

  1625     done

  1626 qed

  1627

  1628 lemma islimpt_in_closure: "(x islimpt S) = (x:closure(S-{x}))"

  1629   unfolding closure_def using islimpt_punctured by blast

  1630

  1631

  1632 subsection {* Frontier (aka boundary) *}

  1633

  1634 definition "frontier S = closure S - interior S"

  1635

  1636 lemma frontier_closed: "closed (frontier S)"

  1637   by (simp add: frontier_def closed_Diff)

  1638

  1639 lemma frontier_closures: "frontier S = (closure S) \<inter> (closure(- S))"

  1640   by (auto simp add: frontier_def interior_closure)

  1641

  1642 lemma frontier_straddle:

  1643   fixes a :: "'a::metric_space"

  1644   shows "a \<in> frontier S \<longleftrightarrow> (\<forall>e>0. (\<exists>x\<in>S. dist a x < e) \<and> (\<exists>x. x \<notin> S \<and> dist a x < e))"

  1645   unfolding frontier_def closure_interior

  1646   by (auto simp add: mem_interior subset_eq ball_def)

  1647

  1648 lemma frontier_subset_closed: "closed S \<Longrightarrow> frontier S \<subseteq> S"

  1649   by (metis frontier_def closure_closed Diff_subset)

  1650

  1651 lemma frontier_empty[simp]: "frontier {} = {}"

  1652   by (simp add: frontier_def)

  1653

  1654 lemma frontier_subset_eq: "frontier S \<subseteq> S \<longleftrightarrow> closed S"

  1655 proof-

  1656   {

  1657     assume "frontier S \<subseteq> S"

  1658     then have "closure S \<subseteq> S"

  1659       using interior_subset unfolding frontier_def by auto

  1660     then have "closed S"

  1661       using closure_subset_eq by auto

  1662   }

  1663   then show ?thesis using frontier_subset_closed[of S] ..

  1664 qed

  1665

  1666 lemma frontier_complement: "frontier(- S) = frontier S"

  1667   by (auto simp add: frontier_def closure_complement interior_complement)

  1668

  1669 lemma frontier_disjoint_eq: "frontier S \<inter> S = {} \<longleftrightarrow> open S"

  1670   using frontier_complement frontier_subset_eq[of "- S"]

  1671   unfolding open_closed by auto

  1672

  1673 subsection {* Filters and the eventually true'' quantifier *}

  1674

  1675 definition indirection :: "'a::real_normed_vector \<Rightarrow> 'a \<Rightarrow> 'a filter"

  1676     (infixr "indirection" 70)

  1677   where "a indirection v = at a within {b. \<exists>c\<ge>0. b - a = scaleR c v}"

  1678

  1679 text {* Identify Trivial limits, where we can't approach arbitrarily closely. *}

  1680

  1681 lemma trivial_limit_within: "trivial_limit (at a within S) \<longleftrightarrow> \<not> a islimpt S"

  1682 proof

  1683   assume "trivial_limit (at a within S)"

  1684   then show "\<not> a islimpt S"

  1685     unfolding trivial_limit_def

  1686     unfolding eventually_at_topological

  1687     unfolding islimpt_def

  1688     apply (clarsimp simp add: set_eq_iff)

  1689     apply (rename_tac T, rule_tac x=T in exI)

  1690     apply (clarsimp, drule_tac x=y in bspec, simp_all)

  1691     done

  1692 next

  1693   assume "\<not> a islimpt S"

  1694   then show "trivial_limit (at a within S)"

  1695     unfolding trivial_limit_def eventually_at_topological islimpt_def

  1696     by metis

  1697 qed

  1698

  1699 lemma trivial_limit_at_iff: "trivial_limit (at a) \<longleftrightarrow> \<not> a islimpt UNIV"

  1700   using trivial_limit_within [of a UNIV] by simp

  1701

  1702 lemma trivial_limit_at:

  1703   fixes a :: "'a::perfect_space"

  1704   shows "\<not> trivial_limit (at a)"

  1705   by (rule at_neq_bot)

  1706

  1707 lemma trivial_limit_at_infinity:

  1708   "\<not> trivial_limit (at_infinity :: ('a::{real_normed_vector,perfect_space}) filter)"

  1709   unfolding trivial_limit_def eventually_at_infinity

  1710   apply clarsimp

  1711   apply (subgoal_tac "\<exists>x::'a. x \<noteq> 0", clarify)

  1712    apply (rule_tac x="scaleR (b / norm x) x" in exI, simp)

  1713   apply (cut_tac islimpt_UNIV [of "0::'a", unfolded islimpt_def])

  1714   apply (drule_tac x=UNIV in spec, simp)

  1715   done

  1716

  1717 lemma not_trivial_limit_within: "\<not> trivial_limit (at x within S) = (x \<in> closure (S - {x}))"

  1718   using islimpt_in_closure

  1719   by (metis trivial_limit_within)

  1720

  1721 text {* Some property holds "sufficiently close" to the limit point. *}

  1722

  1723 lemma eventually_at2:

  1724   "eventually P (at a) \<longleftrightarrow> (\<exists>d>0. \<forall>x. 0 < dist x a \<and> dist x a < d \<longrightarrow> P x)"

  1725   unfolding eventually_at dist_nz by auto

  1726

  1727 lemma eventually_happens: "eventually P net \<Longrightarrow> trivial_limit net \<or> (\<exists>x. P x)"

  1728   unfolding trivial_limit_def

  1729   by (auto elim: eventually_rev_mp)

  1730

  1731 lemma trivial_limit_eventually: "trivial_limit net \<Longrightarrow> eventually P net"

  1732   by simp

  1733

  1734 lemma trivial_limit_eq: "trivial_limit net \<longleftrightarrow> (\<forall>P. eventually P net)"

  1735   by (simp add: filter_eq_iff)

  1736

  1737 text{* Combining theorems for "eventually" *}

  1738

  1739 lemma eventually_rev_mono:

  1740   "eventually P net \<Longrightarrow> (\<forall>x. P x \<longrightarrow> Q x) \<Longrightarrow> eventually Q net"

  1741   using eventually_mono [of P Q] by fast

  1742

  1743 lemma not_eventually: "(\<forall>x. \<not> P x ) \<Longrightarrow> \<not> trivial_limit net \<Longrightarrow> \<not> eventually (\<lambda>x. P x) net"

  1744   by (simp add: eventually_False)

  1745

  1746

  1747 subsection {* Limits *}

  1748

  1749 lemma Lim:

  1750   "(f ---> l) net \<longleftrightarrow>

  1751         trivial_limit net \<or>

  1752         (\<forall>e>0. eventually (\<lambda>x. dist (f x) l < e) net)"

  1753   unfolding tendsto_iff trivial_limit_eq by auto

  1754

  1755 text{* Show that they yield usual definitions in the various cases. *}

  1756

  1757 lemma Lim_within_le: "(f ---> l)(at a within S) \<longleftrightarrow>

  1758     (\<forall>e>0. \<exists>d>0. \<forall>x\<in>S. 0 < dist x a \<and> dist x a \<le> d \<longrightarrow> dist (f x) l < e)"

  1759   by (auto simp add: tendsto_iff eventually_at_le dist_nz)

  1760

  1761 lemma Lim_within: "(f ---> l) (at a within S) \<longleftrightarrow>

  1762     (\<forall>e >0. \<exists>d>0. \<forall>x \<in> S. 0 < dist x a \<and> dist x a  < d \<longrightarrow> dist (f x) l < e)"

  1763   by (auto simp add: tendsto_iff eventually_at dist_nz)

  1764

  1765 lemma Lim_at: "(f ---> l) (at a) \<longleftrightarrow>

  1766     (\<forall>e >0. \<exists>d>0. \<forall>x. 0 < dist x a \<and> dist x a < d  \<longrightarrow> dist (f x) l < e)"

  1767   by (auto simp add: tendsto_iff eventually_at2)

  1768

  1769 lemma Lim_at_infinity:

  1770   "(f ---> l) at_infinity \<longleftrightarrow> (\<forall>e>0. \<exists>b. \<forall>x. norm x \<ge> b \<longrightarrow> dist (f x) l < e)"

  1771   by (auto simp add: tendsto_iff eventually_at_infinity)

  1772

  1773 lemma Lim_eventually: "eventually (\<lambda>x. f x = l) net \<Longrightarrow> (f ---> l) net"

  1774   by (rule topological_tendstoI, auto elim: eventually_rev_mono)

  1775

  1776 text{* The expected monotonicity property. *}

  1777

  1778 lemma Lim_Un:

  1779   assumes "(f ---> l) (at x within S)" "(f ---> l) (at x within T)"

  1780   shows "(f ---> l) (at x within (S \<union> T))"

  1781   using assms unfolding at_within_union by (rule filterlim_sup)

  1782

  1783 lemma Lim_Un_univ:

  1784   "(f ---> l) (at x within S) \<Longrightarrow> (f ---> l) (at x within T) \<Longrightarrow>

  1785     S \<union> T = UNIV \<Longrightarrow> (f ---> l) (at x)"

  1786   by (metis Lim_Un)

  1787

  1788 text{* Interrelations between restricted and unrestricted limits. *}

  1789

  1790 lemma Lim_at_within: (* FIXME: rename *)

  1791   "(f ---> l) (at x) \<Longrightarrow> (f ---> l) (at x within S)"

  1792   by (metis order_refl filterlim_mono subset_UNIV at_le)

  1793

  1794 lemma eventually_within_interior:

  1795   assumes "x \<in> interior S"

  1796   shows "eventually P (at x within S) \<longleftrightarrow> eventually P (at x)"

  1797   (is "?lhs = ?rhs")

  1798 proof

  1799   from assms obtain T where T: "open T" "x \<in> T" "T \<subseteq> S" ..

  1800   {

  1801     assume "?lhs"

  1802     then obtain A where "open A" and "x \<in> A" and "\<forall>y\<in>A. y \<noteq> x \<longrightarrow> y \<in> S \<longrightarrow> P y"

  1803       unfolding eventually_at_topological

  1804       by auto

  1805     with T have "open (A \<inter> T)" and "x \<in> A \<inter> T" and "\<forall>y \<in> A \<inter> T. y \<noteq> x \<longrightarrow> P y"

  1806       by auto

  1807     then show "?rhs"

  1808       unfolding eventually_at_topological by auto

  1809   next

  1810     assume "?rhs"

  1811     then show "?lhs"

  1812       by (auto elim: eventually_elim1 simp: eventually_at_filter)

  1813   }

  1814 qed

  1815

  1816 lemma at_within_interior:

  1817   "x \<in> interior S \<Longrightarrow> at x within S = at x"

  1818   unfolding filter_eq_iff by (intro allI eventually_within_interior)

  1819

  1820 lemma Lim_within_LIMSEQ:

  1821   fixes a :: "'a::first_countable_topology"

  1822   assumes "\<forall>S. (\<forall>n. S n \<noteq> a \<and> S n \<in> T) \<and> S ----> a \<longrightarrow> (\<lambda>n. X (S n)) ----> L"

  1823   shows "(X ---> L) (at a within T)"

  1824   using assms unfolding tendsto_def [where l=L]

  1825   by (simp add: sequentially_imp_eventually_within)

  1826

  1827 lemma Lim_right_bound:

  1828   fixes f :: "'a :: {linorder_topology, conditionally_complete_linorder, no_top} \<Rightarrow>

  1829     'b::{linorder_topology, conditionally_complete_linorder}"

  1830   assumes mono: "\<And>a b. a \<in> I \<Longrightarrow> b \<in> I \<Longrightarrow> x < a \<Longrightarrow> a \<le> b \<Longrightarrow> f a \<le> f b"

  1831     and bnd: "\<And>a. a \<in> I \<Longrightarrow> x < a \<Longrightarrow> K \<le> f a"

  1832   shows "(f ---> Inf (f  ({x<..} \<inter> I))) (at x within ({x<..} \<inter> I))"

  1833 proof (cases "{x<..} \<inter> I = {}")

  1834   case True

  1835   then show ?thesis by simp

  1836 next

  1837   case False

  1838   show ?thesis

  1839   proof (rule order_tendstoI)

  1840     fix a

  1841     assume a: "a < Inf (f  ({x<..} \<inter> I))"

  1842     {

  1843       fix y

  1844       assume "y \<in> {x<..} \<inter> I"

  1845       with False bnd have "Inf (f  ({x<..} \<inter> I)) \<le> f y"

  1846         by (auto intro!: cInf_lower bdd_belowI2 simp del: Inf_image_eq)

  1847       with a have "a < f y"

  1848         by (blast intro: less_le_trans)

  1849     }

  1850     then show "eventually (\<lambda>x. a < f x) (at x within ({x<..} \<inter> I))"

  1851       by (auto simp: eventually_at_filter intro: exI[of _ 1] zero_less_one)

  1852   next

  1853     fix a

  1854     assume "Inf (f  ({x<..} \<inter> I)) < a"

  1855     from cInf_lessD[OF _ this] False obtain y where y: "x < y" "y \<in> I" "f y < a"

  1856       by auto

  1857     then have "eventually (\<lambda>x. x \<in> I \<longrightarrow> f x < a) (at_right x)"

  1858       unfolding eventually_at_right by (metis less_imp_le le_less_trans mono)

  1859     then show "eventually (\<lambda>x. f x < a) (at x within ({x<..} \<inter> I))"

  1860       unfolding eventually_at_filter by eventually_elim simp

  1861   qed

  1862 qed

  1863

  1864 text{* Another limit point characterization. *}

  1865

  1866 lemma islimpt_sequential:

  1867   fixes x :: "'a::first_countable_topology"

  1868   shows "x islimpt S \<longleftrightarrow> (\<exists>f. (\<forall>n::nat. f n \<in> S - {x}) \<and> (f ---> x) sequentially)"

  1869     (is "?lhs = ?rhs")

  1870 proof

  1871   assume ?lhs

  1872   from countable_basis_at_decseq[of x] obtain A where A:

  1873       "\<And>i. open (A i)"

  1874       "\<And>i. x \<in> A i"

  1875       "\<And>S. open S \<Longrightarrow> x \<in> S \<Longrightarrow> eventually (\<lambda>i. A i \<subseteq> S) sequentially"

  1876     by blast

  1877   def f \<equiv> "\<lambda>n. SOME y. y \<in> S \<and> y \<in> A n \<and> x \<noteq> y"

  1878   {

  1879     fix n

  1880     from ?lhs have "\<exists>y. y \<in> S \<and> y \<in> A n \<and> x \<noteq> y"

  1881       unfolding islimpt_def using A(1,2)[of n] by auto

  1882     then have "f n \<in> S \<and> f n \<in> A n \<and> x \<noteq> f n"

  1883       unfolding f_def by (rule someI_ex)

  1884     then have "f n \<in> S" "f n \<in> A n" "x \<noteq> f n" by auto

  1885   }

  1886   then have "\<forall>n. f n \<in> S - {x}" by auto

  1887   moreover have "(\<lambda>n. f n) ----> x"

  1888   proof (rule topological_tendstoI)

  1889     fix S

  1890     assume "open S" "x \<in> S"

  1891     from A(3)[OF this] \<And>n. f n \<in> A n

  1892     show "eventually (\<lambda>x. f x \<in> S) sequentially"

  1893       by (auto elim!: eventually_elim1)

  1894   qed

  1895   ultimately show ?rhs by fast

  1896 next

  1897   assume ?rhs

  1898   then obtain f :: "nat \<Rightarrow> 'a" where f: "\<And>n. f n \<in> S - {x}" and lim: "f ----> x"

  1899     by auto

  1900   show ?lhs

  1901     unfolding islimpt_def

  1902   proof safe

  1903     fix T

  1904     assume "open T" "x \<in> T"

  1905     from lim[THEN topological_tendstoD, OF this] f

  1906     show "\<exists>y\<in>S. y \<in> T \<and> y \<noteq> x"

  1907       unfolding eventually_sequentially by auto

  1908   qed

  1909 qed

  1910

  1911 lemma Lim_null:

  1912   fixes f :: "'a \<Rightarrow> 'b::real_normed_vector"

  1913   shows "(f ---> l) net \<longleftrightarrow> ((\<lambda>x. f(x) - l) ---> 0) net"

  1914   by (simp add: Lim dist_norm)

  1915

  1916 lemma Lim_null_comparison:

  1917   fixes f :: "'a \<Rightarrow> 'b::real_normed_vector"

  1918   assumes "eventually (\<lambda>x. norm (f x) \<le> g x) net" "(g ---> 0) net"

  1919   shows "(f ---> 0) net"

  1920   using assms(2)

  1921 proof (rule metric_tendsto_imp_tendsto)

  1922   show "eventually (\<lambda>x. dist (f x) 0 \<le> dist (g x) 0) net"

  1923     using assms(1) by (rule eventually_elim1) (simp add: dist_norm)

  1924 qed

  1925

  1926 lemma Lim_transform_bound:

  1927   fixes f :: "'a \<Rightarrow> 'b::real_normed_vector"

  1928     and g :: "'a \<Rightarrow> 'c::real_normed_vector"

  1929   assumes "eventually (\<lambda>n. norm (f n) \<le> norm (g n)) net"

  1930     and "(g ---> 0) net"

  1931   shows "(f ---> 0) net"

  1932   using assms(1) tendsto_norm_zero [OF assms(2)]

  1933   by (rule Lim_null_comparison)

  1934

  1935 text{* Deducing things about the limit from the elements. *}

  1936

  1937 lemma Lim_in_closed_set:

  1938   assumes "closed S"

  1939     and "eventually (\<lambda>x. f(x) \<in> S) net"

  1940     and "\<not> trivial_limit net" "(f ---> l) net"

  1941   shows "l \<in> S"

  1942 proof (rule ccontr)

  1943   assume "l \<notin> S"

  1944   with closed S have "open (- S)" "l \<in> - S"

  1945     by (simp_all add: open_Compl)

  1946   with assms(4) have "eventually (\<lambda>x. f x \<in> - S) net"

  1947     by (rule topological_tendstoD)

  1948   with assms(2) have "eventually (\<lambda>x. False) net"

  1949     by (rule eventually_elim2) simp

  1950   with assms(3) show "False"

  1951     by (simp add: eventually_False)

  1952 qed

  1953

  1954 text{* Need to prove closed(cball(x,e)) before deducing this as a corollary. *}

  1955

  1956 lemma Lim_dist_ubound:

  1957   assumes "\<not>(trivial_limit net)"

  1958     and "(f ---> l) net"

  1959     and "eventually (\<lambda>x. dist a (f x) \<le> e) net"

  1960   shows "dist a l \<le> e"

  1961   using assms by (fast intro: tendsto_le tendsto_intros)

  1962

  1963 lemma Lim_norm_ubound:

  1964   fixes f :: "'a \<Rightarrow> 'b::real_normed_vector"

  1965   assumes "\<not>(trivial_limit net)" "(f ---> l) net" "eventually (\<lambda>x. norm(f x) \<le> e) net"

  1966   shows "norm(l) \<le> e"

  1967   using assms by (fast intro: tendsto_le tendsto_intros)

  1968

  1969 lemma Lim_norm_lbound:

  1970   fixes f :: "'a \<Rightarrow> 'b::real_normed_vector"

  1971   assumes "\<not> trivial_limit net"

  1972     and "(f ---> l) net"

  1973     and "eventually (\<lambda>x. e \<le> norm (f x)) net"

  1974   shows "e \<le> norm l"

  1975   using assms by (fast intro: tendsto_le tendsto_intros)

  1976

  1977 text{* Limit under bilinear function *}

  1978

  1979 lemma Lim_bilinear:

  1980   assumes "(f ---> l) net"

  1981     and "(g ---> m) net"

  1982     and "bounded_bilinear h"

  1983   shows "((\<lambda>x. h (f x) (g x)) ---> (h l m)) net"

  1984   using bounded_bilinear h (f ---> l) net (g ---> m) net

  1985   by (rule bounded_bilinear.tendsto)

  1986

  1987 text{* These are special for limits out of the same vector space. *}

  1988

  1989 lemma Lim_within_id: "(id ---> a) (at a within s)"

  1990   unfolding id_def by (rule tendsto_ident_at)

  1991

  1992 lemma Lim_at_id: "(id ---> a) (at a)"

  1993   unfolding id_def by (rule tendsto_ident_at)

  1994

  1995 lemma Lim_at_zero:

  1996   fixes a :: "'a::real_normed_vector"

  1997     and l :: "'b::topological_space"

  1998   shows "(f ---> l) (at a) \<longleftrightarrow> ((\<lambda>x. f(a + x)) ---> l) (at 0)"

  1999   using LIM_offset_zero LIM_offset_zero_cancel ..

  2000

  2001 text{* It's also sometimes useful to extract the limit point from the filter. *}

  2002

  2003 abbreviation netlimit :: "'a::t2_space filter \<Rightarrow> 'a"

  2004   where "netlimit F \<equiv> Lim F (\<lambda>x. x)"

  2005

  2006 lemma netlimit_within: "\<not> trivial_limit (at a within S) \<Longrightarrow> netlimit (at a within S) = a"

  2007   by (rule tendsto_Lim) (auto intro: tendsto_intros)

  2008

  2009 lemma netlimit_at:

  2010   fixes a :: "'a::{perfect_space,t2_space}"

  2011   shows "netlimit (at a) = a"

  2012   using netlimit_within [of a UNIV] by simp

  2013

  2014 lemma lim_within_interior:

  2015   "x \<in> interior S \<Longrightarrow> (f ---> l) (at x within S) \<longleftrightarrow> (f ---> l) (at x)"

  2016   by (metis at_within_interior)

  2017

  2018 lemma netlimit_within_interior:

  2019   fixes x :: "'a::{t2_space,perfect_space}"

  2020   assumes "x \<in> interior S"

  2021   shows "netlimit (at x within S) = x"

  2022   using assms by (metis at_within_interior netlimit_at)

  2023

  2024 text{* Transformation of limit. *}

  2025

  2026 lemma Lim_transform:

  2027   fixes f g :: "'a::type \<Rightarrow> 'b::real_normed_vector"

  2028   assumes "((\<lambda>x. f x - g x) ---> 0) net" "(f ---> l) net"

  2029   shows "(g ---> l) net"

  2030   using tendsto_diff [OF assms(2) assms(1)] by simp

  2031

  2032 lemma Lim_transform_eventually:

  2033   "eventually (\<lambda>x. f x = g x) net \<Longrightarrow> (f ---> l) net \<Longrightarrow> (g ---> l) net"

  2034   apply (rule topological_tendstoI)

  2035   apply (drule (2) topological_tendstoD)

  2036   apply (erule (1) eventually_elim2, simp)

  2037   done

  2038

  2039 lemma Lim_transform_within:

  2040   assumes "0 < d"

  2041     and "\<forall>x'\<in>S. 0 < dist x' x \<and> dist x' x < d \<longrightarrow> f x' = g x'"

  2042     and "(f ---> l) (at x within S)"

  2043   shows "(g ---> l) (at x within S)"

  2044 proof (rule Lim_transform_eventually)

  2045   show "eventually (\<lambda>x. f x = g x) (at x within S)"

  2046     using assms(1,2) by (auto simp: dist_nz eventually_at)

  2047   show "(f ---> l) (at x within S)" by fact

  2048 qed

  2049

  2050 lemma Lim_transform_at:

  2051   assumes "0 < d"

  2052     and "\<forall>x'. 0 < dist x' x \<and> dist x' x < d \<longrightarrow> f x' = g x'"

  2053     and "(f ---> l) (at x)"

  2054   shows "(g ---> l) (at x)"

  2055   using _ assms(3)

  2056 proof (rule Lim_transform_eventually)

  2057   show "eventually (\<lambda>x. f x = g x) (at x)"

  2058     unfolding eventually_at2

  2059     using assms(1,2) by auto

  2060 qed

  2061

  2062 text{* Common case assuming being away from some crucial point like 0. *}

  2063

  2064 lemma Lim_transform_away_within:

  2065   fixes a b :: "'a::t1_space"

  2066   assumes "a \<noteq> b"

  2067     and "\<forall>x\<in>S. x \<noteq> a \<and> x \<noteq> b \<longrightarrow> f x = g x"

  2068     and "(f ---> l) (at a within S)"

  2069   shows "(g ---> l) (at a within S)"

  2070 proof (rule Lim_transform_eventually)

  2071   show "(f ---> l) (at a within S)" by fact

  2072   show "eventually (\<lambda>x. f x = g x) (at a within S)"

  2073     unfolding eventually_at_topological

  2074     by (rule exI [where x="- {b}"], simp add: open_Compl assms)

  2075 qed

  2076

  2077 lemma Lim_transform_away_at:

  2078   fixes a b :: "'a::t1_space"

  2079   assumes ab: "a\<noteq>b"

  2080     and fg: "\<forall>x. x \<noteq> a \<and> x \<noteq> b \<longrightarrow> f x = g x"

  2081     and fl: "(f ---> l) (at a)"

  2082   shows "(g ---> l) (at a)"

  2083   using Lim_transform_away_within[OF ab, of UNIV f g l] fg fl by simp

  2084

  2085 text{* Alternatively, within an open set. *}

  2086

  2087 lemma Lim_transform_within_open:

  2088   assumes "open S" and "a \<in> S"

  2089     and "\<forall>x\<in>S. x \<noteq> a \<longrightarrow> f x = g x"

  2090     and "(f ---> l) (at a)"

  2091   shows "(g ---> l) (at a)"

  2092 proof (rule Lim_transform_eventually)

  2093   show "eventually (\<lambda>x. f x = g x) (at a)"

  2094     unfolding eventually_at_topological

  2095     using assms(1,2,3) by auto

  2096   show "(f ---> l) (at a)" by fact

  2097 qed

  2098

  2099 text{* A congruence rule allowing us to transform limits assuming not at point. *}

  2100

  2101 (* FIXME: Only one congruence rule for tendsto can be used at a time! *)

  2102

  2103 lemma Lim_cong_within(*[cong add]*):

  2104   assumes "a = b"

  2105     and "x = y"

  2106     and "S = T"

  2107     and "\<And>x. x \<noteq> b \<Longrightarrow> x \<in> T \<Longrightarrow> f x = g x"

  2108   shows "(f ---> x) (at a within S) \<longleftrightarrow> (g ---> y) (at b within T)"

  2109   unfolding tendsto_def eventually_at_topological

  2110   using assms by simp

  2111

  2112 lemma Lim_cong_at(*[cong add]*):

  2113   assumes "a = b" "x = y"

  2114     and "\<And>x. x \<noteq> a \<Longrightarrow> f x = g x"

  2115   shows "((\<lambda>x. f x) ---> x) (at a) \<longleftrightarrow> ((g ---> y) (at a))"

  2116   unfolding tendsto_def eventually_at_topological

  2117   using assms by simp

  2118

  2119 text{* Useful lemmas on closure and set of possible sequential limits.*}

  2120

  2121 lemma closure_sequential:

  2122   fixes l :: "'a::first_countable_topology"

  2123   shows "l \<in> closure S \<longleftrightarrow> (\<exists>x. (\<forall>n. x n \<in> S) \<and> (x ---> l) sequentially)"

  2124   (is "?lhs = ?rhs")

  2125 proof

  2126   assume "?lhs"

  2127   moreover

  2128   {

  2129     assume "l \<in> S"

  2130     then have "?rhs" using tendsto_const[of l sequentially] by auto

  2131   }

  2132   moreover

  2133   {

  2134     assume "l islimpt S"

  2135     then have "?rhs" unfolding islimpt_sequential by auto

  2136   }

  2137   ultimately show "?rhs"

  2138     unfolding closure_def by auto

  2139 next

  2140   assume "?rhs"

  2141   then show "?lhs" unfolding closure_def islimpt_sequential by auto

  2142 qed

  2143

  2144 lemma closed_sequential_limits:

  2145   fixes S :: "'a::first_countable_topology set"

  2146   shows "closed S \<longleftrightarrow> (\<forall>x l. (\<forall>n. x n \<in> S) \<and> (x ---> l) sequentially \<longrightarrow> l \<in> S)"

  2147 by (metis closure_sequential closure_subset_eq subset_iff)

  2148

  2149 lemma closure_approachable:

  2150   fixes S :: "'a::metric_space set"

  2151   shows "x \<in> closure S \<longleftrightarrow> (\<forall>e>0. \<exists>y\<in>S. dist y x < e)"

  2152   apply (auto simp add: closure_def islimpt_approachable)

  2153   apply (metis dist_self)

  2154   done

  2155

  2156 lemma closed_approachable:

  2157   fixes S :: "'a::metric_space set"

  2158   shows "closed S \<Longrightarrow> (\<forall>e>0. \<exists>y\<in>S. dist y x < e) \<longleftrightarrow> x \<in> S"

  2159   by (metis closure_closed closure_approachable)

  2160

  2161 lemma closure_contains_Inf:

  2162   fixes S :: "real set"

  2163   assumes "S \<noteq> {}" "bdd_below S"

  2164   shows "Inf S \<in> closure S"

  2165 proof -

  2166   have *: "\<forall>x\<in>S. Inf S \<le> x"

  2167     using cInf_lower[of _ S] assms by metis

  2168   {

  2169     fix e :: real

  2170     assume "e > 0"

  2171     then have "Inf S < Inf S + e" by simp

  2172     with assms obtain x where "x \<in> S" "x < Inf S + e"

  2173       by (subst (asm) cInf_less_iff) auto

  2174     with * have "\<exists>x\<in>S. dist x (Inf S) < e"

  2175       by (intro bexI[of _ x]) (auto simp add: dist_real_def)

  2176   }

  2177   then show ?thesis unfolding closure_approachable by auto

  2178 qed

  2179

  2180 lemma closed_contains_Inf:

  2181   fixes S :: "real set"

  2182   shows "S \<noteq> {} \<Longrightarrow> bdd_below S \<Longrightarrow> closed S \<Longrightarrow> Inf S \<in> S"

  2183   by (metis closure_contains_Inf closure_closed assms)

  2184

  2185 lemma not_trivial_limit_within_ball:

  2186   "\<not> trivial_limit (at x within S) \<longleftrightarrow> (\<forall>e>0. S \<inter> ball x e - {x} \<noteq> {})"

  2187   (is "?lhs = ?rhs")

  2188 proof -

  2189   {

  2190     assume "?lhs"

  2191     {

  2192       fix e :: real

  2193       assume "e > 0"

  2194       then obtain y where "y \<in> S - {x}" and "dist y x < e"

  2195         using ?lhs not_trivial_limit_within[of x S] closure_approachable[of x "S - {x}"]

  2196         by auto

  2197       then have "y \<in> S \<inter> ball x e - {x}"

  2198         unfolding ball_def by (simp add: dist_commute)

  2199       then have "S \<inter> ball x e - {x} \<noteq> {}" by blast

  2200     }

  2201     then have "?rhs" by auto

  2202   }

  2203   moreover

  2204   {

  2205     assume "?rhs"

  2206     {

  2207       fix e :: real

  2208       assume "e > 0"

  2209       then obtain y where "y \<in> S \<inter> ball x e - {x}"

  2210         using ?rhs by blast

  2211       then have "y \<in> S - {x}" and "dist y x < e"

  2212         unfolding ball_def by (simp_all add: dist_commute)

  2213       then have "\<exists>y \<in> S - {x}. dist y x < e"

  2214         by auto

  2215     }

  2216     then have "?lhs"

  2217       using not_trivial_limit_within[of x S] closure_approachable[of x "S - {x}"]

  2218       by auto

  2219   }

  2220   ultimately show ?thesis by auto

  2221 qed

  2222

  2223

  2224 subsection {* Infimum Distance *}

  2225

  2226 definition "infdist x A = (if A = {} then 0 else INF a:A. dist x a)"

  2227

  2228 lemma bdd_below_infdist[intro, simp]: "bdd_below (dist xA)"

  2229   by (auto intro!: zero_le_dist)

  2230

  2231 lemma infdist_notempty: "A \<noteq> {} \<Longrightarrow> infdist x A = (INF a:A. dist x a)"

  2232   by (simp add: infdist_def)

  2233

  2234 lemma infdist_nonneg: "0 \<le> infdist x A"

  2235   by (auto simp add: infdist_def intro: cINF_greatest)

  2236

  2237 lemma infdist_le: "a \<in> A \<Longrightarrow> infdist x A \<le> dist x a"

  2238   by (auto intro: cINF_lower simp add: infdist_def)

  2239

  2240 lemma infdist_le2: "a \<in> A \<Longrightarrow> dist x a \<le> d \<Longrightarrow> infdist x A \<le> d"

  2241   by (auto intro!: cINF_lower2 simp add: infdist_def)

  2242

  2243 lemma infdist_zero[simp]: "a \<in> A \<Longrightarrow> infdist a A = 0"

  2244   by (auto intro!: antisym infdist_nonneg infdist_le2)

  2245

  2246 lemma infdist_triangle: "infdist x A \<le> infdist y A + dist x y"

  2247 proof (cases "A = {}")

  2248   case True

  2249   then show ?thesis by (simp add: infdist_def)

  2250 next

  2251   case False

  2252   then obtain a where "a \<in> A" by auto

  2253   have "infdist x A \<le> Inf {dist x y + dist y a |a. a \<in> A}"

  2254   proof (rule cInf_greatest)

  2255     from A \<noteq> {} show "{dist x y + dist y a |a. a \<in> A} \<noteq> {}"

  2256       by simp

  2257     fix d

  2258     assume "d \<in> {dist x y + dist y a |a. a \<in> A}"

  2259     then obtain a where d: "d = dist x y + dist y a" "a \<in> A"

  2260       by auto

  2261     show "infdist x A \<le> d"

  2262       unfolding infdist_notempty[OF A \<noteq> {}]

  2263     proof (rule cINF_lower2)

  2264       show "a \<in> A" by fact

  2265       show "dist x a \<le> d"

  2266         unfolding d by (rule dist_triangle)

  2267     qed simp

  2268   qed

  2269   also have "\<dots> = dist x y + infdist y A"

  2270   proof (rule cInf_eq, safe)

  2271     fix a

  2272     assume "a \<in> A"

  2273     then show "dist x y + infdist y A \<le> dist x y + dist y a"

  2274       by (auto intro: infdist_le)

  2275   next

  2276     fix i

  2277     assume inf: "\<And>d. d \<in> {dist x y + dist y a |a. a \<in> A} \<Longrightarrow> i \<le> d"

  2278     then have "i - dist x y \<le> infdist y A"

  2279       unfolding infdist_notempty[OF A \<noteq> {}] using a \<in> A

  2280       by (intro cINF_greatest) (auto simp: field_simps)

  2281     then show "i \<le> dist x y + infdist y A"

  2282       by simp

  2283   qed

  2284   finally show ?thesis by simp

  2285 qed

  2286

  2287 lemma in_closure_iff_infdist_zero:

  2288   assumes "A \<noteq> {}"

  2289   shows "x \<in> closure A \<longleftrightarrow> infdist x A = 0"

  2290 proof

  2291   assume "x \<in> closure A"

  2292   show "infdist x A = 0"

  2293   proof (rule ccontr)

  2294     assume "infdist x A \<noteq> 0"

  2295     with infdist_nonneg[of x A] have "infdist x A > 0"

  2296       by auto

  2297     then have "ball x (infdist x A) \<inter> closure A = {}"

  2298       apply auto

  2299       apply (metis x \<in> closure A closure_approachable dist_commute infdist_le not_less)

  2300       done

  2301     then have "x \<notin> closure A"

  2302       by (metis 0 < infdist x A centre_in_ball disjoint_iff_not_equal)

  2303     then show False using x \<in> closure A by simp

  2304   qed

  2305 next

  2306   assume x: "infdist x A = 0"

  2307   then obtain a where "a \<in> A"

  2308     by atomize_elim (metis all_not_in_conv assms)

  2309   show "x \<in> closure A"

  2310     unfolding closure_approachable

  2311     apply safe

  2312   proof (rule ccontr)

  2313     fix e :: real

  2314     assume "e > 0"

  2315     assume "\<not> (\<exists>y\<in>A. dist y x < e)"

  2316     then have "infdist x A \<ge> e" using a \<in> A

  2317       unfolding infdist_def

  2318       by (force simp: dist_commute intro: cINF_greatest)

  2319     with x e > 0 show False by auto

  2320   qed

  2321 qed

  2322

  2323 lemma in_closed_iff_infdist_zero:

  2324   assumes "closed A" "A \<noteq> {}"

  2325   shows "x \<in> A \<longleftrightarrow> infdist x A = 0"

  2326 proof -

  2327   have "x \<in> closure A \<longleftrightarrow> infdist x A = 0"

  2328     by (rule in_closure_iff_infdist_zero) fact

  2329   with assms show ?thesis by simp

  2330 qed

  2331

  2332 lemma tendsto_infdist [tendsto_intros]:

  2333   assumes f: "(f ---> l) F"

  2334   shows "((\<lambda>x. infdist (f x) A) ---> infdist l A) F"

  2335 proof (rule tendstoI)

  2336   fix e ::real

  2337   assume "e > 0"

  2338   from tendstoD[OF f this]

  2339   show "eventually (\<lambda>x. dist (infdist (f x) A) (infdist l A) < e) F"

  2340   proof (eventually_elim)

  2341     fix x

  2342     from infdist_triangle[of l A "f x"] infdist_triangle[of "f x" A l]

  2343     have "dist (infdist (f x) A) (infdist l A) \<le> dist (f x) l"

  2344       by (simp add: dist_commute dist_real_def)

  2345     also assume "dist (f x) l < e"

  2346     finally show "dist (infdist (f x) A) (infdist l A) < e" .

  2347   qed

  2348 qed

  2349

  2350 text{* Some other lemmas about sequences. *}

  2351

  2352 lemma sequentially_offset: (* TODO: move to Topological_Spaces.thy *)

  2353   assumes "eventually (\<lambda>i. P i) sequentially"

  2354   shows "eventually (\<lambda>i. P (i + k)) sequentially"

  2355   using assms by (rule eventually_sequentially_seg [THEN iffD2])

  2356

  2357 lemma seq_offset_neg: (* TODO: move to Topological_Spaces.thy *)

  2358   "(f ---> l) sequentially \<Longrightarrow> ((\<lambda>i. f(i - k)) ---> l) sequentially"

  2359   apply (erule filterlim_compose)

  2360   apply (simp add: filterlim_def le_sequentially eventually_filtermap eventually_sequentially)

  2361   apply arith

  2362   done

  2363

  2364 lemma seq_harmonic: "((\<lambda>n. inverse (real n)) ---> 0) sequentially"

  2365   using LIMSEQ_inverse_real_of_nat by (rule LIMSEQ_imp_Suc) (* TODO: move to Limits.thy *)

  2366

  2367 subsection {* More properties of closed balls *}

  2368

  2369 lemma closed_vimage: (* TODO: move to Topological_Spaces.thy *)

  2370   assumes "closed s" and "continuous_on UNIV f"

  2371   shows "closed (vimage f s)"

  2372   using assms unfolding continuous_on_closed_vimage [OF closed_UNIV]

  2373   by simp

  2374

  2375 lemma closed_cball: "closed (cball x e)"

  2376 proof -

  2377   have "closed (dist x - {..e})"

  2378     by (intro closed_vimage closed_atMost continuous_intros)

  2379   also have "dist x - {..e} = cball x e"

  2380     by auto

  2381   finally show ?thesis .

  2382 qed

  2383

  2384 lemma open_contains_cball: "open S \<longleftrightarrow> (\<forall>x\<in>S. \<exists>e>0.  cball x e \<subseteq> S)"

  2385 proof -

  2386   {

  2387     fix x and e::real

  2388     assume "x\<in>S" "e>0" "ball x e \<subseteq> S"

  2389     then have "\<exists>d>0. cball x d \<subseteq> S" unfolding subset_eq by (rule_tac x="e/2" in exI, auto)

  2390   }

  2391   moreover

  2392   {

  2393     fix x and e::real

  2394     assume "x\<in>S" "e>0" "cball x e \<subseteq> S"

  2395     then have "\<exists>d>0. ball x d \<subseteq> S"

  2396       unfolding subset_eq

  2397       apply(rule_tac x="e/2" in exI)

  2398       apply auto

  2399       done

  2400   }

  2401   ultimately show ?thesis

  2402     unfolding open_contains_ball by auto

  2403 qed

  2404

  2405 lemma open_contains_cball_eq: "open S \<Longrightarrow> (\<forall>x. x \<in> S \<longleftrightarrow> (\<exists>e>0. cball x e \<subseteq> S))"

  2406   by (metis open_contains_cball subset_eq order_less_imp_le centre_in_cball)

  2407

  2408 lemma mem_interior_cball: "x \<in> interior S \<longleftrightarrow> (\<exists>e>0. cball x e \<subseteq> S)"

  2409   apply (simp add: interior_def, safe)

  2410   apply (force simp add: open_contains_cball)

  2411   apply (rule_tac x="ball x e" in exI)

  2412   apply (simp add: subset_trans [OF ball_subset_cball])

  2413   done

  2414

  2415 lemma islimpt_ball:

  2416   fixes x y :: "'a::{real_normed_vector,perfect_space}"

  2417   shows "y islimpt ball x e \<longleftrightarrow> 0 < e \<and> y \<in> cball x e"

  2418   (is "?lhs = ?rhs")

  2419 proof

  2420   assume "?lhs"

  2421   {

  2422     assume "e \<le> 0"

  2423     then have *:"ball x e = {}"

  2424       using ball_eq_empty[of x e] by auto

  2425     have False using ?lhs

  2426       unfolding * using islimpt_EMPTY[of y] by auto

  2427   }

  2428   then have "e > 0" by (metis not_less)

  2429   moreover

  2430   have "y \<in> cball x e"

  2431     using closed_cball[of x e] islimpt_subset[of y "ball x e" "cball x e"]

  2432       ball_subset_cball[of x e] ?lhs

  2433     unfolding closed_limpt by auto

  2434   ultimately show "?rhs" by auto

  2435 next

  2436   assume "?rhs"

  2437   then have "e > 0" by auto

  2438   {

  2439     fix d :: real

  2440     assume "d > 0"

  2441     have "\<exists>x'\<in>ball x e. x' \<noteq> y \<and> dist x' y < d"

  2442     proof (cases "d \<le> dist x y")

  2443       case True

  2444       then show "\<exists>x'\<in>ball x e. x' \<noteq> y \<and> dist x' y < d"

  2445       proof (cases "x = y")

  2446         case True

  2447         then have False

  2448           using d \<le> dist x y d>0 by auto

  2449         then show "\<exists>x'\<in>ball x e. x' \<noteq> y \<and> dist x' y < d"

  2450           by auto

  2451       next

  2452         case False

  2453         have "dist x (y - (d / (2 * dist y x)) *\<^sub>R (y - x)) =

  2454           norm (x - y + (d / (2 * norm (y - x))) *\<^sub>R (y - x))"

  2455           unfolding mem_cball mem_ball dist_norm diff_diff_eq2 diff_add_eq[symmetric]

  2456           by auto

  2457         also have "\<dots> = \<bar>- 1 + d / (2 * norm (x - y))\<bar> * norm (x - y)"

  2458           using scaleR_left_distrib[of "- 1" "d / (2 * norm (y - x))", symmetric, of "y - x"]

  2459           unfolding scaleR_minus_left scaleR_one

  2460           by (auto simp add: norm_minus_commute)

  2461         also have "\<dots> = \<bar>- norm (x - y) + d / 2\<bar>"

  2462           unfolding abs_mult_pos[of "norm (x - y)", OF norm_ge_zero[of "x - y"]]

  2463           unfolding distrib_right using x\<noteq>y[unfolded dist_nz, unfolded dist_norm]

  2464           by auto

  2465         also have "\<dots> \<le> e - d/2" using d \<le> dist x y and d>0 and ?rhs

  2466           by (auto simp add: dist_norm)

  2467         finally have "y - (d / (2 * dist y x)) *\<^sub>R (y - x) \<in> ball x e" using d>0

  2468           by auto

  2469         moreover

  2470         have "(d / (2*dist y x)) *\<^sub>R (y - x) \<noteq> 0"

  2471           using x\<noteq>y[unfolded dist_nz] d>0 unfolding scaleR_eq_0_iff

  2472           by (auto simp add: dist_commute)

  2473         moreover

  2474         have "dist (y - (d / (2 * dist y x)) *\<^sub>R (y - x)) y < d"

  2475           unfolding dist_norm

  2476           apply simp

  2477           unfolding norm_minus_cancel

  2478           using d > 0 x\<noteq>y[unfolded dist_nz] dist_commute[of x y]

  2479           unfolding dist_norm

  2480           apply auto

  2481           done

  2482         ultimately show "\<exists>x'\<in>ball x e. x' \<noteq> y \<and> dist x' y < d"

  2483           apply (rule_tac x = "y - (d / (2*dist y x)) *\<^sub>R (y - x)" in bexI)

  2484           apply auto

  2485           done

  2486       qed

  2487     next

  2488       case False

  2489       then have "d > dist x y" by auto

  2490       show "\<exists>x' \<in> ball x e. x' \<noteq> y \<and> dist x' y < d"

  2491       proof (cases "x = y")

  2492         case True

  2493         obtain z where **: "z \<noteq> y" "dist z y < min e d"

  2494           using perfect_choose_dist[of "min e d" y]

  2495           using d > 0 e>0 by auto

  2496         show "\<exists>x'\<in>ball x e. x' \<noteq> y \<and> dist x' y < d"

  2497           unfolding x = y

  2498           using z \<noteq> y **

  2499           apply (rule_tac x=z in bexI)

  2500           apply (auto simp add: dist_commute)

  2501           done

  2502       next

  2503         case False

  2504         then show "\<exists>x'\<in>ball x e. x' \<noteq> y \<and> dist x' y < d"

  2505           using d>0 d > dist x y ?rhs

  2506           apply (rule_tac x=x in bexI)

  2507           apply auto

  2508           done

  2509       qed

  2510     qed

  2511   }

  2512   then show "?lhs"

  2513     unfolding mem_cball islimpt_approachable mem_ball by auto

  2514 qed

  2515

  2516 lemma closure_ball_lemma:

  2517   fixes x y :: "'a::real_normed_vector"

  2518   assumes "x \<noteq> y"

  2519   shows "y islimpt ball x (dist x y)"

  2520 proof (rule islimptI)

  2521   fix T

  2522   assume "y \<in> T" "open T"

  2523   then obtain r where "0 < r" "\<forall>z. dist z y < r \<longrightarrow> z \<in> T"

  2524     unfolding open_dist by fast

  2525   (* choose point between x and y, within distance r of y. *)

  2526   def k \<equiv> "min 1 (r / (2 * dist x y))"

  2527   def z \<equiv> "y + scaleR k (x - y)"

  2528   have z_def2: "z = x + scaleR (1 - k) (y - x)"

  2529     unfolding z_def by (simp add: algebra_simps)

  2530   have "dist z y < r"

  2531     unfolding z_def k_def using 0 < r

  2532     by (simp add: dist_norm min_def)

  2533   then have "z \<in> T"

  2534     using \<forall>z. dist z y < r \<longrightarrow> z \<in> T by simp

  2535   have "dist x z < dist x y"

  2536     unfolding z_def2 dist_norm

  2537     apply (simp add: norm_minus_commute)

  2538     apply (simp only: dist_norm [symmetric])

  2539     apply (subgoal_tac "\<bar>1 - k\<bar> * dist x y < 1 * dist x y", simp)

  2540     apply (rule mult_strict_right_mono)

  2541     apply (simp add: k_def zero_less_dist_iff 0 < r x \<noteq> y)

  2542     apply (simp add: zero_less_dist_iff x \<noteq> y)

  2543     done

  2544   then have "z \<in> ball x (dist x y)"

  2545     by simp

  2546   have "z \<noteq> y"

  2547     unfolding z_def k_def using x \<noteq> y 0 < r

  2548     by (simp add: min_def)

  2549   show "\<exists>z\<in>ball x (dist x y). z \<in> T \<and> z \<noteq> y"

  2550     using z \<in> ball x (dist x y) z \<in> T z \<noteq> y

  2551     by fast

  2552 qed

  2553

  2554 lemma closure_ball:

  2555   fixes x :: "'a::real_normed_vector"

  2556   shows "0 < e \<Longrightarrow> closure (ball x e) = cball x e"

  2557   apply (rule equalityI)

  2558   apply (rule closure_minimal)

  2559   apply (rule ball_subset_cball)

  2560   apply (rule closed_cball)

  2561   apply (rule subsetI, rename_tac y)

  2562   apply (simp add: le_less [where 'a=real])

  2563   apply (erule disjE)

  2564   apply (rule subsetD [OF closure_subset], simp)

  2565   apply (simp add: closure_def)

  2566   apply clarify

  2567   apply (rule closure_ball_lemma)

  2568   apply (simp add: zero_less_dist_iff)

  2569   done

  2570

  2571 (* In a trivial vector space, this fails for e = 0. *)

  2572 lemma interior_cball:

  2573   fixes x :: "'a::{real_normed_vector, perfect_space}"

  2574   shows "interior (cball x e) = ball x e"

  2575 proof (cases "e \<ge> 0")

  2576   case False note cs = this

  2577   from cs have "ball x e = {}"

  2578     using ball_empty[of e x] by auto

  2579   moreover

  2580   {

  2581     fix y

  2582     assume "y \<in> cball x e"

  2583     then have False

  2584       unfolding mem_cball using dist_nz[of x y] cs by auto

  2585   }

  2586   then have "cball x e = {}" by auto

  2587   then have "interior (cball x e) = {}"

  2588     using interior_empty by auto

  2589   ultimately show ?thesis by blast

  2590 next

  2591   case True note cs = this

  2592   have "ball x e \<subseteq> cball x e"

  2593     using ball_subset_cball by auto

  2594   moreover

  2595   {

  2596     fix S y

  2597     assume as: "S \<subseteq> cball x e" "open S" "y\<in>S"

  2598     then obtain d where "d>0" and d: "\<forall>x'. dist x' y < d \<longrightarrow> x' \<in> S"

  2599       unfolding open_dist by blast

  2600     then obtain xa where xa_y: "xa \<noteq> y" and xa: "dist xa y < d"

  2601       using perfect_choose_dist [of d] by auto

  2602     have "xa \<in> S"

  2603       using d[THEN spec[where x = xa]]

  2604       using xa by (auto simp add: dist_commute)

  2605     then have xa_cball: "xa \<in> cball x e"

  2606       using as(1) by auto

  2607     then have "y \<in> ball x e"

  2608     proof (cases "x = y")

  2609       case True

  2610       then have "e > 0"

  2611         using xa_y[unfolded dist_nz] xa_cball[unfolded mem_cball]

  2612         by (auto simp add: dist_commute)

  2613       then show "y \<in> ball x e"

  2614         using x = y  by simp

  2615     next

  2616       case False

  2617       have "dist (y + (d / 2 / dist y x) *\<^sub>R (y - x)) y < d"

  2618         unfolding dist_norm

  2619         using d>0 norm_ge_zero[of "y - x"] x \<noteq> y by auto

  2620       then have *: "y + (d / 2 / dist y x) *\<^sub>R (y - x) \<in> cball x e"

  2621         using d as(1)[unfolded subset_eq] by blast

  2622       have "y - x \<noteq> 0" using x \<noteq> y by auto

  2623       hence **:"d / (2 * norm (y - x)) > 0"

  2624         unfolding zero_less_norm_iff[symmetric] using d>0 by auto

  2625       have "dist (y + (d / 2 / dist y x) *\<^sub>R (y - x)) x =

  2626         norm (y + (d / (2 * norm (y - x))) *\<^sub>R y - (d / (2 * norm (y - x))) *\<^sub>R x - x)"

  2627         by (auto simp add: dist_norm algebra_simps)

  2628       also have "\<dots> = norm ((1 + d / (2 * norm (y - x))) *\<^sub>R (y - x))"

  2629         by (auto simp add: algebra_simps)

  2630       also have "\<dots> = \<bar>1 + d / (2 * norm (y - x))\<bar> * norm (y - x)"

  2631         using ** by auto

  2632       also have "\<dots> = (dist y x) + d/2"

  2633         using ** by (auto simp add: distrib_right dist_norm)

  2634       finally have "e \<ge> dist x y +d/2"

  2635         using *[unfolded mem_cball] by (auto simp add: dist_commute)

  2636       then show "y \<in> ball x e"

  2637         unfolding mem_ball using d>0 by auto

  2638     qed

  2639   }

  2640   then have "\<forall>S \<subseteq> cball x e. open S \<longrightarrow> S \<subseteq> ball x e"

  2641     by auto

  2642   ultimately show ?thesis

  2643     using interior_unique[of "ball x e" "cball x e"]

  2644     using open_ball[of x e]

  2645     by auto

  2646 qed

  2647

  2648 lemma frontier_ball:

  2649   fixes a :: "'a::real_normed_vector"

  2650   shows "0 < e \<Longrightarrow> frontier(ball a e) = {x. dist a x = e}"

  2651   apply (simp add: frontier_def closure_ball interior_open order_less_imp_le)

  2652   apply (simp add: set_eq_iff)

  2653   apply arith

  2654   done

  2655

  2656 lemma frontier_cball:

  2657   fixes a :: "'a::{real_normed_vector, perfect_space}"

  2658   shows "frontier (cball a e) = {x. dist a x = e}"

  2659   apply (simp add: frontier_def interior_cball closed_cball order_less_imp_le)

  2660   apply (simp add: set_eq_iff)

  2661   apply arith

  2662   done

  2663

  2664 lemma cball_eq_empty: "cball x e = {} \<longleftrightarrow> e < 0"

  2665   apply (simp add: set_eq_iff not_le)

  2666   apply (metis zero_le_dist dist_self order_less_le_trans)

  2667   done

  2668

  2669 lemma cball_empty: "e < 0 \<Longrightarrow> cball x e = {}"

  2670   by (simp add: cball_eq_empty)

  2671

  2672 lemma cball_eq_sing:

  2673   fixes x :: "'a::{metric_space,perfect_space}"

  2674   shows "cball x e = {x} \<longleftrightarrow> e = 0"

  2675 proof (rule linorder_cases)

  2676   assume e: "0 < e"

  2677   obtain a where "a \<noteq> x" "dist a x < e"

  2678     using perfect_choose_dist [OF e] by auto

  2679   then have "a \<noteq> x" "dist x a \<le> e"

  2680     by (auto simp add: dist_commute)

  2681   with e show ?thesis by (auto simp add: set_eq_iff)

  2682 qed auto

  2683

  2684 lemma cball_sing:

  2685   fixes x :: "'a::metric_space"

  2686   shows "e = 0 \<Longrightarrow> cball x e = {x}"

  2687   by (auto simp add: set_eq_iff)

  2688

  2689

  2690 subsection {* Boundedness *}

  2691

  2692   (* FIXME: This has to be unified with BSEQ!! *)

  2693 definition (in metric_space) bounded :: "'a set \<Rightarrow> bool"

  2694   where "bounded S \<longleftrightarrow> (\<exists>x e. \<forall>y\<in>S. dist x y \<le> e)"

  2695

  2696 lemma bounded_subset_cball: "bounded S \<longleftrightarrow> (\<exists>e x. S \<subseteq> cball x e)"

  2697   unfolding bounded_def subset_eq by auto

  2698

  2699 lemma bounded_any_center: "bounded S \<longleftrightarrow> (\<exists>e. \<forall>y\<in>S. dist a y \<le> e)"

  2700   unfolding bounded_def

  2701   by auto (metis add_commute add_le_cancel_right dist_commute dist_triangle_le)

  2702

  2703 lemma bounded_iff: "bounded S \<longleftrightarrow> (\<exists>a. \<forall>x\<in>S. norm x \<le> a)"

  2704   unfolding bounded_any_center [where a=0]

  2705   by (simp add: dist_norm)

  2706

  2707 lemma bounded_realI:

  2708   assumes "\<forall>x\<in>s. abs (x::real) \<le> B"

  2709   shows "bounded s"

  2710   unfolding bounded_def dist_real_def

  2711   by (metis abs_minus_commute assms diff_0_right)

  2712

  2713 lemma bounded_empty [simp]: "bounded {}"

  2714   by (simp add: bounded_def)

  2715

  2716 lemma bounded_subset: "bounded T \<Longrightarrow> S \<subseteq> T \<Longrightarrow> bounded S"

  2717   by (metis bounded_def subset_eq)

  2718

  2719 lemma bounded_interior[intro]: "bounded S \<Longrightarrow> bounded(interior S)"

  2720   by (metis bounded_subset interior_subset)

  2721

  2722 lemma bounded_closure[intro]:

  2723   assumes "bounded S"

  2724   shows "bounded (closure S)"

  2725 proof -

  2726   from assms obtain x and a where a: "\<forall>y\<in>S. dist x y \<le> a"

  2727     unfolding bounded_def by auto

  2728   {

  2729     fix y

  2730     assume "y \<in> closure S"

  2731     then obtain f where f: "\<forall>n. f n \<in> S"  "(f ---> y) sequentially"

  2732       unfolding closure_sequential by auto

  2733     have "\<forall>n. f n \<in> S \<longrightarrow> dist x (f n) \<le> a" using a by simp

  2734     then have "eventually (\<lambda>n. dist x (f n) \<le> a) sequentially"

  2735       by (rule eventually_mono, simp add: f(1))

  2736     have "dist x y \<le> a"

  2737       apply (rule Lim_dist_ubound [of sequentially f])

  2738       apply (rule trivial_limit_sequentially)

  2739       apply (rule f(2))

  2740       apply fact

  2741       done

  2742   }

  2743   then show ?thesis

  2744     unfolding bounded_def by auto

  2745 qed

  2746

  2747 lemma bounded_cball[simp,intro]: "bounded (cball x e)"

  2748   apply (simp add: bounded_def)

  2749   apply (rule_tac x=x in exI)

  2750   apply (rule_tac x=e in exI)

  2751   apply auto

  2752   done

  2753

  2754 lemma bounded_ball[simp,intro]: "bounded (ball x e)"

  2755   by (metis ball_subset_cball bounded_cball bounded_subset)

  2756

  2757 lemma bounded_Un[simp]: "bounded (S \<union> T) \<longleftrightarrow> bounded S \<and> bounded T"

  2758   apply (auto simp add: bounded_def)

  2759   by (metis Un_iff add_le_cancel_left dist_triangle le_max_iff_disj max.order_iff)

  2760

  2761 lemma bounded_Union[intro]: "finite F \<Longrightarrow> \<forall>S\<in>F. bounded S \<Longrightarrow> bounded (\<Union>F)"

  2762   by (induct rule: finite_induct[of F]) auto

  2763

  2764 lemma bounded_UN [intro]: "finite A \<Longrightarrow> \<forall>x\<in>A. bounded (B x) \<Longrightarrow> bounded (\<Union>x\<in>A. B x)"

  2765   by (induct set: finite) auto

  2766

  2767 lemma bounded_insert [simp]: "bounded (insert x S) \<longleftrightarrow> bounded S"

  2768 proof -

  2769   have "\<forall>y\<in>{x}. dist x y \<le> 0"

  2770     by simp

  2771   then have "bounded {x}"

  2772     unfolding bounded_def by fast

  2773   then show ?thesis

  2774     by (metis insert_is_Un bounded_Un)

  2775 qed

  2776

  2777 lemma finite_imp_bounded [intro]: "finite S \<Longrightarrow> bounded S"

  2778   by (induct set: finite) simp_all

  2779

  2780 lemma bounded_pos: "bounded S \<longleftrightarrow> (\<exists>b>0. \<forall>x\<in> S. norm x \<le> b)"

  2781   apply (simp add: bounded_iff)

  2782   apply (subgoal_tac "\<And>x (y::real). 0 < 1 + abs y \<and> (x \<le> y \<longrightarrow> x \<le> 1 + abs y)")

  2783   apply metis

  2784   apply arith

  2785   done

  2786

  2787 lemma Bseq_eq_bounded:

  2788   fixes f :: "nat \<Rightarrow> 'a::real_normed_vector"

  2789   shows "Bseq f \<longleftrightarrow> bounded (range f)"

  2790   unfolding Bseq_def bounded_pos by auto

  2791

  2792 lemma bounded_Int[intro]: "bounded S \<or> bounded T \<Longrightarrow> bounded (S \<inter> T)"

  2793   by (metis Int_lower1 Int_lower2 bounded_subset)

  2794

  2795 lemma bounded_diff[intro]: "bounded S \<Longrightarrow> bounded (S - T)"

  2796   by (metis Diff_subset bounded_subset)

  2797

  2798 lemma not_bounded_UNIV[simp, intro]:

  2799   "\<not> bounded (UNIV :: 'a::{real_normed_vector, perfect_space} set)"

  2800 proof (auto simp add: bounded_pos not_le)

  2801   obtain x :: 'a where "x \<noteq> 0"

  2802     using perfect_choose_dist [OF zero_less_one] by fast

  2803   fix b :: real

  2804   assume b: "b >0"

  2805   have b1: "b +1 \<ge> 0"

  2806     using b by simp

  2807   with x \<noteq> 0 have "b < norm (scaleR (b + 1) (sgn x))"

  2808     by (simp add: norm_sgn)

  2809   then show "\<exists>x::'a. b < norm x" ..

  2810 qed

  2811

  2812 lemma bounded_linear_image:

  2813   assumes "bounded S"

  2814     and "bounded_linear f"

  2815   shows "bounded (f  S)"

  2816 proof -

  2817   from assms(1) obtain b where b: "b > 0" "\<forall>x\<in>S. norm x \<le> b"

  2818     unfolding bounded_pos by auto

  2819   from assms(2) obtain B where B: "B > 0" "\<forall>x. norm (f x) \<le> B * norm x"

  2820     using bounded_linear.pos_bounded by (auto simp add: mult_ac)

  2821   {

  2822     fix x

  2823     assume "x \<in> S"

  2824     then have "norm x \<le> b"

  2825       using b by auto

  2826     then have "norm (f x) \<le> B * b"

  2827       using B(2)

  2828       apply (erule_tac x=x in allE)

  2829       apply (metis B(1) B(2) order_trans mult_le_cancel_left_pos)

  2830       done

  2831   }

  2832   then show ?thesis

  2833     unfolding bounded_pos

  2834     apply (rule_tac x="b*B" in exI)

  2835     using b B by (auto simp add: mult_commute)

  2836 qed

  2837

  2838 lemma bounded_scaling:

  2839   fixes S :: "'a::real_normed_vector set"

  2840   shows "bounded S \<Longrightarrow> bounded ((\<lambda>x. c *\<^sub>R x)  S)"

  2841   apply (rule bounded_linear_image)

  2842   apply assumption

  2843   apply (rule bounded_linear_scaleR_right)

  2844   done

  2845

  2846 lemma bounded_translation:

  2847   fixes S :: "'a::real_normed_vector set"

  2848   assumes "bounded S"

  2849   shows "bounded ((\<lambda>x. a + x)  S)"

  2850 proof -

  2851   from assms obtain b where b: "b > 0" "\<forall>x\<in>S. norm x \<le> b"

  2852     unfolding bounded_pos by auto

  2853   {

  2854     fix x

  2855     assume "x \<in> S"

  2856     then have "norm (a + x) \<le> b + norm a"

  2857       using norm_triangle_ineq[of a x] b by auto

  2858   }

  2859   then show ?thesis

  2860     unfolding bounded_pos

  2861     using norm_ge_zero[of a] b(1) and add_strict_increasing[of b 0 "norm a"]

  2862     by (auto intro!: exI[of _ "b + norm a"])

  2863 qed

  2864

  2865

  2866 text{* Some theorems on sups and infs using the notion "bounded". *}

  2867

  2868 lemma bounded_real: "bounded (S::real set) \<longleftrightarrow> (\<exists>a. \<forall>x\<in>S. \<bar>x\<bar> \<le> a)"

  2869   by (simp add: bounded_iff)

  2870

  2871 lemma bounded_imp_bdd_above: "bounded S \<Longrightarrow> bdd_above (S :: real set)"

  2872   by (auto simp: bounded_def bdd_above_def dist_real_def)

  2873      (metis abs_le_D1 abs_minus_commute diff_le_eq)

  2874

  2875 lemma bounded_imp_bdd_below: "bounded S \<Longrightarrow> bdd_below (S :: real set)"

  2876   by (auto simp: bounded_def bdd_below_def dist_real_def)

  2877      (metis abs_le_D1 add_commute diff_le_eq)

  2878

  2879 (* TODO: remove the following lemmas about Inf and Sup, is now in conditionally complete lattice *)

  2880

  2881 lemma bounded_has_Sup:

  2882   fixes S :: "real set"

  2883   assumes "bounded S"

  2884     and "S \<noteq> {}"

  2885   shows "\<forall>x\<in>S. x \<le> Sup S"

  2886     and "\<forall>b. (\<forall>x\<in>S. x \<le> b) \<longrightarrow> Sup S \<le> b"

  2887 proof

  2888   show "\<forall>b. (\<forall>x\<in>S. x \<le> b) \<longrightarrow> Sup S \<le> b"

  2889     using assms by (metis cSup_least)

  2890 qed (metis cSup_upper assms(1) bounded_imp_bdd_above)

  2891

  2892 lemma Sup_insert:

  2893   fixes S :: "real set"

  2894   shows "bounded S \<Longrightarrow> Sup (insert x S) = (if S = {} then x else max x (Sup S))"

  2895   by (auto simp: bounded_imp_bdd_above sup_max cSup_insert_If)

  2896

  2897 lemma Sup_insert_finite:

  2898   fixes S :: "real set"

  2899   shows "finite S \<Longrightarrow> Sup (insert x S) = (if S = {} then x else max x (Sup S))"

  2900   apply (rule Sup_insert)

  2901   apply (rule finite_imp_bounded)

  2902   apply simp

  2903   done

  2904

  2905 lemma bounded_has_Inf:

  2906   fixes S :: "real set"

  2907   assumes "bounded S"

  2908     and "S \<noteq> {}"

  2909   shows "\<forall>x\<in>S. x \<ge> Inf S"

  2910     and "\<forall>b. (\<forall>x\<in>S. x \<ge> b) \<longrightarrow> Inf S \<ge> b"

  2911 proof

  2912   show "\<forall>b. (\<forall>x\<in>S. x \<ge> b) \<longrightarrow> Inf S \<ge> b"

  2913     using assms by (metis cInf_greatest)

  2914 qed (metis cInf_lower assms(1) bounded_imp_bdd_below)

  2915

  2916 lemma Inf_insert:

  2917   fixes S :: "real set"

  2918   shows "bounded S \<Longrightarrow> Inf (insert x S) = (if S = {} then x else min x (Inf S))"

  2919   by (auto simp: bounded_imp_bdd_below inf_min cInf_insert_If)

  2920

  2921 lemma Inf_insert_finite:

  2922   fixes S :: "real set"

  2923   shows "finite S \<Longrightarrow> Inf (insert x S) = (if S = {} then x else min x (Inf S))"

  2924   apply (rule Inf_insert)

  2925   apply (rule finite_imp_bounded)

  2926   apply simp

  2927   done

  2928

  2929 subsection {* Compactness *}

  2930

  2931 subsubsection {* Bolzano-Weierstrass property *}

  2932

  2933 lemma heine_borel_imp_bolzano_weierstrass:

  2934   assumes "compact s"

  2935     and "infinite t"

  2936     and "t \<subseteq> s"

  2937   shows "\<exists>x \<in> s. x islimpt t"

  2938 proof (rule ccontr)

  2939   assume "\<not> (\<exists>x \<in> s. x islimpt t)"

  2940   then obtain f where f: "\<forall>x\<in>s. x \<in> f x \<and> open (f x) \<and> (\<forall>y\<in>t. y \<in> f x \<longrightarrow> y = x)"

  2941     unfolding islimpt_def

  2942     using bchoice[of s "\<lambda> x T. x \<in> T \<and> open T \<and> (\<forall>y\<in>t. y \<in> T \<longrightarrow> y = x)"]

  2943     by auto

  2944   obtain g where g: "g \<subseteq> {t. \<exists>x. x \<in> s \<and> t = f x}" "finite g" "s \<subseteq> \<Union>g"

  2945     using assms(1)[unfolded compact_eq_heine_borel, THEN spec[where x="{t. \<exists>x. x\<in>s \<and> t = f x}"]]

  2946     using f by auto

  2947   from g(1,3) have g':"\<forall>x\<in>g. \<exists>xa \<in> s. x = f xa"

  2948     by auto

  2949   {

  2950     fix x y

  2951     assume "x \<in> t" "y \<in> t" "f x = f y"

  2952     then have "x \<in> f x"  "y \<in> f x \<longrightarrow> y = x"

  2953       using f[THEN bspec[where x=x]] and t \<subseteq> s by auto

  2954     then have "x = y"

  2955       using f x = f y and f[THEN bspec[where x=y]] and y \<in> t and t \<subseteq> s

  2956       by auto

  2957   }

  2958   then have "inj_on f t"

  2959     unfolding inj_on_def by simp

  2960   then have "infinite (f  t)"

  2961     using assms(2) using finite_imageD by auto

  2962   moreover

  2963   {

  2964     fix x

  2965     assume "x \<in> t" "f x \<notin> g"

  2966     from g(3) assms(3) x \<in> t obtain h where "h \<in> g" and "x \<in> h"

  2967       by auto

  2968     then obtain y where "y \<in> s" "h = f y"

  2969       using g'[THEN bspec[where x=h]] by auto

  2970     then have "y = x"

  2971       using f[THEN bspec[where x=y]] and x\<in>t and x\<in>h[unfolded h = f y]

  2972       by auto

  2973     then have False

  2974       using f x \<notin> g h \<in> g unfolding h = f y

  2975       by auto

  2976   }

  2977   then have "f  t \<subseteq> g" by auto

  2978   ultimately show False

  2979     using g(2) using finite_subset by auto

  2980 qed

  2981

  2982 lemma acc_point_range_imp_convergent_subsequence:

  2983   fixes l :: "'a :: first_countable_topology"

  2984   assumes l: "\<forall>U. l\<in>U \<longrightarrow> open U \<longrightarrow> infinite (U \<inter> range f)"

  2985   shows "\<exists>r. subseq r \<and> (f \<circ> r) ----> l"

  2986 proof -

  2987   from countable_basis_at_decseq[of l]

  2988   obtain A where A:

  2989       "\<And>i. open (A i)"

  2990       "\<And>i. l \<in> A i"

  2991       "\<And>S. open S \<Longrightarrow> l \<in> S \<Longrightarrow> eventually (\<lambda>i. A i \<subseteq> S) sequentially"

  2992     by blast

  2993   def s \<equiv> "\<lambda>n i. SOME j. i < j \<and> f j \<in> A (Suc n)"

  2994   {

  2995     fix n i

  2996     have "infinite (A (Suc n) \<inter> range f - f{.. i})"

  2997       using l A by auto

  2998     then have "\<exists>x. x \<in> A (Suc n) \<inter> range f - f{.. i}"

  2999       unfolding ex_in_conv by (intro notI) simp

  3000     then have "\<exists>j. f j \<in> A (Suc n) \<and> j \<notin> {.. i}"

  3001       by auto

  3002     then have "\<exists>a. i < a \<and> f a \<in> A (Suc n)"

  3003       by (auto simp: not_le)

  3004     then have "i < s n i" "f (s n i) \<in> A (Suc n)"

  3005       unfolding s_def by (auto intro: someI2_ex)

  3006   }

  3007   note s = this

  3008   def r \<equiv> "rec_nat (s 0 0) s"

  3009   have "subseq r"

  3010     by (auto simp: r_def s subseq_Suc_iff)

  3011   moreover

  3012   have "(\<lambda>n. f (r n)) ----> l"

  3013   proof (rule topological_tendstoI)

  3014     fix S

  3015     assume "open S" "l \<in> S"

  3016     with A(3) have "eventually (\<lambda>i. A i \<subseteq> S) sequentially"

  3017       by auto

  3018     moreover

  3019     {

  3020       fix i

  3021       assume "Suc 0 \<le> i"

  3022       then have "f (r i) \<in> A i"

  3023         by (cases i) (simp_all add: r_def s)

  3024     }

  3025     then have "eventually (\<lambda>i. f (r i) \<in> A i) sequentially"

  3026       by (auto simp: eventually_sequentially)

  3027     ultimately show "eventually (\<lambda>i. f (r i) \<in> S) sequentially"

  3028       by eventually_elim auto

  3029   qed

  3030   ultimately show "\<exists>r. subseq r \<and> (f \<circ> r) ----> l"

  3031     by (auto simp: convergent_def comp_def)

  3032 qed

  3033

  3034 lemma sequence_infinite_lemma:

  3035   fixes f :: "nat \<Rightarrow> 'a::t1_space"

  3036   assumes "\<forall>n. f n \<noteq> l"

  3037     and "(f ---> l) sequentially"

  3038   shows "infinite (range f)"

  3039 proof

  3040   assume "finite (range f)"

  3041   then have "closed (range f)"

  3042     by (rule finite_imp_closed)

  3043   then have "open (- range f)"

  3044     by (rule open_Compl)

  3045   from assms(1) have "l \<in> - range f"

  3046     by auto

  3047   from assms(2) have "eventually (\<lambda>n. f n \<in> - range f) sequentially"

  3048     using open (- range f) l \<in> - range f

  3049     by (rule topological_tendstoD)

  3050   then show False

  3051     unfolding eventually_sequentially

  3052     by auto

  3053 qed

  3054

  3055 lemma closure_insert:

  3056   fixes x :: "'a::t1_space"

  3057   shows "closure (insert x s) = insert x (closure s)"

  3058   apply (rule closure_unique)

  3059   apply (rule insert_mono [OF closure_subset])

  3060   apply (rule closed_insert [OF closed_closure])

  3061   apply (simp add: closure_minimal)

  3062   done

  3063

  3064 lemma islimpt_insert:

  3065   fixes x :: "'a::t1_space"

  3066   shows "x islimpt (insert a s) \<longleftrightarrow> x islimpt s"

  3067 proof

  3068   assume *: "x islimpt (insert a s)"

  3069   show "x islimpt s"

  3070   proof (rule islimptI)

  3071     fix t

  3072     assume t: "x \<in> t" "open t"

  3073     show "\<exists>y\<in>s. y \<in> t \<and> y \<noteq> x"

  3074     proof (cases "x = a")

  3075       case True

  3076       obtain y where "y \<in> insert a s" "y \<in> t" "y \<noteq> x"

  3077         using * t by (rule islimptE)

  3078       with x = a show ?thesis by auto

  3079     next

  3080       case False

  3081       with t have t': "x \<in> t - {a}" "open (t - {a})"

  3082         by (simp_all add: open_Diff)

  3083       obtain y where "y \<in> insert a s" "y \<in> t - {a}" "y \<noteq> x"

  3084         using * t' by (rule islimptE)

  3085       then show ?thesis by auto

  3086     qed

  3087   qed

  3088 next

  3089   assume "x islimpt s"

  3090   then show "x islimpt (insert a s)"

  3091     by (rule islimpt_subset) auto

  3092 qed

  3093

  3094 lemma islimpt_finite:

  3095   fixes x :: "'a::t1_space"

  3096   shows "finite s \<Longrightarrow> \<not> x islimpt s"

  3097   by (induct set: finite) (simp_all add: islimpt_insert)

  3098

  3099 lemma islimpt_union_finite:

  3100   fixes x :: "'a::t1_space"

  3101   shows "finite s \<Longrightarrow> x islimpt (s \<union> t) \<longleftrightarrow> x islimpt t"

  3102   by (simp add: islimpt_Un islimpt_finite)

  3103

  3104 lemma islimpt_eq_acc_point:

  3105   fixes l :: "'a :: t1_space"

  3106   shows "l islimpt S \<longleftrightarrow> (\<forall>U. l\<in>U \<longrightarrow> open U \<longrightarrow> infinite (U \<inter> S))"

  3107 proof (safe intro!: islimptI)

  3108   fix U

  3109   assume "l islimpt S" "l \<in> U" "open U" "finite (U \<inter> S)"

  3110   then have "l islimpt S" "l \<in> (U - (U \<inter> S - {l}))" "open (U - (U \<inter> S - {l}))"

  3111     by (auto intro: finite_imp_closed)

  3112   then show False

  3113     by (rule islimptE) auto

  3114 next

  3115   fix T

  3116   assume *: "\<forall>U. l\<in>U \<longrightarrow> open U \<longrightarrow> infinite (U \<inter> S)" "l \<in> T" "open T"

  3117   then have "infinite (T \<inter> S - {l})"

  3118     by auto

  3119   then have "\<exists>x. x \<in> (T \<inter> S - {l})"

  3120     unfolding ex_in_conv by (intro notI) simp

  3121   then show "\<exists>y\<in>S. y \<in> T \<and> y \<noteq> l"

  3122     by auto

  3123 qed

  3124

  3125 lemma islimpt_range_imp_convergent_subsequence:

  3126   fixes l :: "'a :: {t1_space, first_countable_topology}"

  3127   assumes l: "l islimpt (range f)"

  3128   shows "\<exists>r. subseq r \<and> (f \<circ> r) ----> l"

  3129   using l unfolding islimpt_eq_acc_point

  3130   by (rule acc_point_range_imp_convergent_subsequence)

  3131

  3132 lemma sequence_unique_limpt:

  3133   fixes f :: "nat \<Rightarrow> 'a::t2_space"

  3134   assumes "(f ---> l) sequentially"

  3135     and "l' islimpt (range f)"

  3136   shows "l' = l"

  3137 proof (rule ccontr)

  3138   assume "l' \<noteq> l"

  3139   obtain s t where "open s" "open t" "l' \<in> s" "l \<in> t" "s \<inter> t = {}"

  3140     using hausdorff [OF l' \<noteq> l] by auto

  3141   have "eventually (\<lambda>n. f n \<in> t) sequentially"

  3142     using assms(1) open t l \<in> t by (rule topological_tendstoD)

  3143   then obtain N where "\<forall>n\<ge>N. f n \<in> t"

  3144     unfolding eventually_sequentially by auto

  3145

  3146   have "UNIV = {..<N} \<union> {N..}"

  3147     by auto

  3148   then have "l' islimpt (f  ({..<N} \<union> {N..}))"

  3149     using assms(2) by simp

  3150   then have "l' islimpt (f  {..<N} \<union> f  {N..})"

  3151     by (simp add: image_Un)

  3152   then have "l' islimpt (f  {N..})"

  3153     by (simp add: islimpt_union_finite)

  3154   then obtain y where "y \<in> f  {N..}" "y \<in> s" "y \<noteq> l'"

  3155     using l' \<in> s open s by (rule islimptE)

  3156   then obtain n where "N \<le> n" "f n \<in> s" "f n \<noteq> l'"

  3157     by auto

  3158   with \<forall>n\<ge>N. f n \<in> t have "f n \<in> s \<inter> t"

  3159     by simp

  3160   with s \<inter> t = {} show False

  3161     by simp

  3162 qed

  3163

  3164 lemma bolzano_weierstrass_imp_closed:

  3165   fixes s :: "'a::{first_countable_topology,t2_space} set"

  3166   assumes "\<forall>t. infinite t \<and> t \<subseteq> s --> (\<exists>x \<in> s. x islimpt t)"

  3167   shows "closed s"

  3168 proof -

  3169   {

  3170     fix x l

  3171     assume as: "\<forall>n::nat. x n \<in> s" "(x ---> l) sequentially"

  3172     then have "l \<in> s"

  3173     proof (cases "\<forall>n. x n \<noteq> l")

  3174       case False

  3175       then show "l\<in>s" using as(1) by auto

  3176     next

  3177       case True note cas = this

  3178       with as(2) have "infinite (range x)"

  3179         using sequence_infinite_lemma[of x l] by auto

  3180       then obtain l' where "l'\<in>s" "l' islimpt (range x)"

  3181         using assms[THEN spec[where x="range x"]] as(1) by auto

  3182       then show "l\<in>s" using sequence_unique_limpt[of x l l']

  3183         using as cas by auto

  3184     qed

  3185   }

  3186   then show ?thesis

  3187     unfolding closed_sequential_limits by fast

  3188 qed

  3189

  3190 lemma compact_imp_bounded:

  3191   assumes "compact U"

  3192   shows "bounded U"

  3193 proof -

  3194   have "compact U" "\<forall>x\<in>U. open (ball x 1)" "U \<subseteq> (\<Union>x\<in>U. ball x 1)"

  3195     using assms by auto

  3196   then obtain D where D: "D \<subseteq> U" "finite D" "U \<subseteq> (\<Union>x\<in>D. ball x 1)"

  3197     by (rule compactE_image)

  3198   from finite D have "bounded (\<Union>x\<in>D. ball x 1)"

  3199     by (simp add: bounded_UN)

  3200   then show "bounded U" using U \<subseteq> (\<Union>x\<in>D. ball x 1)

  3201     by (rule bounded_subset)

  3202 qed

  3203

  3204 text{* In particular, some common special cases. *}

  3205

  3206 lemma compact_union [intro]:

  3207   assumes "compact s"

  3208     and "compact t"

  3209   shows " compact (s \<union> t)"

  3210 proof (rule compactI)

  3211   fix f

  3212   assume *: "Ball f open" "s \<union> t \<subseteq> \<Union>f"

  3213   from * compact s obtain s' where "s' \<subseteq> f \<and> finite s' \<and> s \<subseteq> \<Union>s'"

  3214     unfolding compact_eq_heine_borel by (auto elim!: allE[of _ f])

  3215   moreover

  3216   from * compact t obtain t' where "t' \<subseteq> f \<and> finite t' \<and> t \<subseteq> \<Union>t'"

  3217     unfolding compact_eq_heine_borel by (auto elim!: allE[of _ f])

  3218   ultimately show "\<exists>f'\<subseteq>f. finite f' \<and> s \<union> t \<subseteq> \<Union>f'"

  3219     by (auto intro!: exI[of _ "s' \<union> t'"])

  3220 qed

  3221

  3222 lemma compact_Union [intro]: "finite S \<Longrightarrow> (\<And>T. T \<in> S \<Longrightarrow> compact T) \<Longrightarrow> compact (\<Union>S)"

  3223   by (induct set: finite) auto

  3224

  3225 lemma compact_UN [intro]:

  3226   "finite A \<Longrightarrow> (\<And>x. x \<in> A \<Longrightarrow> compact (B x)) \<Longrightarrow> compact (\<Union>x\<in>A. B x)"

  3227   unfolding SUP_def by (rule compact_Union) auto

  3228

  3229 lemma closed_inter_compact [intro]:

  3230   assumes "closed s"

  3231     and "compact t"

  3232   shows "compact (s \<inter> t)"

  3233   using compact_inter_closed [of t s] assms

  3234   by (simp add: Int_commute)

  3235

  3236 lemma compact_inter [intro]:

  3237   fixes s t :: "'a :: t2_space set"

  3238   assumes "compact s"

  3239     and "compact t"

  3240   shows "compact (s \<inter> t)"

  3241   using assms by (intro compact_inter_closed compact_imp_closed)

  3242

  3243 lemma compact_sing [simp]: "compact {a}"

  3244   unfolding compact_eq_heine_borel by auto

  3245

  3246 lemma compact_insert [simp]:

  3247   assumes "compact s"

  3248   shows "compact (insert x s)"

  3249 proof -

  3250   have "compact ({x} \<union> s)"

  3251     using compact_sing assms by (rule compact_union)

  3252   then show ?thesis by simp

  3253 qed

  3254

  3255 lemma finite_imp_compact: "finite s \<Longrightarrow> compact s"

  3256   by (induct set: finite) simp_all

  3257

  3258 lemma open_delete:

  3259   fixes s :: "'a::t1_space set"

  3260   shows "open s \<Longrightarrow> open (s - {x})"

  3261   by (simp add: open_Diff)

  3262

  3263 text{*Compactness expressed with filters*}

  3264

  3265 definition "filter_from_subbase B = Abs_filter (\<lambda>P. \<exists>X \<subseteq> B. finite X \<and> Inf X \<le> P)"

  3266

  3267 lemma eventually_filter_from_subbase:

  3268   "eventually P (filter_from_subbase B) \<longleftrightarrow> (\<exists>X \<subseteq> B. finite X \<and> Inf X \<le> P)"

  3269     (is "_ \<longleftrightarrow> ?R P")

  3270   unfolding filter_from_subbase_def

  3271 proof (rule eventually_Abs_filter is_filter.intro)+

  3272   show "?R (\<lambda>x. True)"

  3273     by (rule exI[of _ "{}"]) (simp add: le_fun_def)

  3274 next

  3275   fix P Q

  3276   assume "?R P" then guess X ..

  3277   moreover

  3278   assume "?R Q" then guess Y ..

  3279   ultimately show "?R (\<lambda>x. P x \<and> Q x)"

  3280     by (intro exI[of _ "X \<union> Y"]) auto

  3281 next

  3282   fix P Q

  3283   assume "?R P" then guess X ..

  3284   moreover assume "\<forall>x. P x \<longrightarrow> Q x"

  3285   ultimately show "?R Q"

  3286     by (intro exI[of _ X]) auto

  3287 qed

  3288

  3289 lemma eventually_filter_from_subbaseI: "P \<in> B \<Longrightarrow> eventually P (filter_from_subbase B)"

  3290   by (subst eventually_filter_from_subbase) (auto intro!: exI[of _ "{P}"])

  3291

  3292 lemma filter_from_subbase_not_bot:

  3293   "\<forall>X \<subseteq> B. finite X \<longrightarrow> Inf X \<noteq> bot \<Longrightarrow> filter_from_subbase B \<noteq> bot"

  3294   unfolding trivial_limit_def eventually_filter_from_subbase

  3295     bot_bool_def [symmetric] bot_fun_def [symmetric] bot_unique by simp

  3296

  3297 lemma closure_iff_nhds_not_empty:

  3298   "x \<in> closure X \<longleftrightarrow> (\<forall>A. \<forall>S\<subseteq>A. open S \<longrightarrow> x \<in> S \<longrightarrow> X \<inter> A \<noteq> {})"

  3299 proof safe

  3300   assume x: "x \<in> closure X"

  3301   fix S A

  3302   assume "open S" "x \<in> S" "X \<inter> A = {}" "S \<subseteq> A"

  3303   then have "x \<notin> closure (-S)"

  3304     by (auto simp: closure_complement subset_eq[symmetric] intro: interiorI)

  3305   with x have "x \<in> closure X - closure (-S)"

  3306     by auto

  3307   also have "\<dots> \<subseteq> closure (X \<inter> S)"

  3308     using open S open_inter_closure_subset[of S X] by (simp add: closed_Compl ac_simps)

  3309   finally have "X \<inter> S \<noteq> {}" by auto

  3310   then show False using X \<inter> A = {} S \<subseteq> A by auto

  3311 next

  3312   assume "\<forall>A S. S \<subseteq> A \<longrightarrow> open S \<longrightarrow> x \<in> S \<longrightarrow> X \<inter> A \<noteq> {}"

  3313   from this[THEN spec, of "- X", THEN spec, of "- closure X"]

  3314   show "x \<in> closure X"

  3315     by (simp add: closure_subset open_Compl)

  3316 qed

  3317

  3318 lemma compact_filter:

  3319   "compact U \<longleftrightarrow> (\<forall>F. F \<noteq> bot \<longrightarrow> eventually (\<lambda>x. x \<in> U) F \<longrightarrow> (\<exists>x\<in>U. inf (nhds x) F \<noteq> bot))"

  3320 proof (intro allI iffI impI compact_fip[THEN iffD2] notI)

  3321   fix F

  3322   assume "compact U"

  3323   assume F: "F \<noteq> bot" "eventually (\<lambda>x. x \<in> U) F"

  3324   then have "U \<noteq> {}"

  3325     by (auto simp: eventually_False)

  3326

  3327   def Z \<equiv> "closure  {A. eventually (\<lambda>x. x \<in> A) F}"

  3328   then have "\<forall>z\<in>Z. closed z"

  3329     by auto

  3330   moreover

  3331   have ev_Z: "\<And>z. z \<in> Z \<Longrightarrow> eventually (\<lambda>x. x \<in> z) F"

  3332     unfolding Z_def by (auto elim: eventually_elim1 intro: set_mp[OF closure_subset])

  3333   have "(\<forall>B \<subseteq> Z. finite B \<longrightarrow> U \<inter> \<Inter>B \<noteq> {})"

  3334   proof (intro allI impI)

  3335     fix B assume "finite B" "B \<subseteq> Z"

  3336     with finite B ev_Z have "eventually (\<lambda>x. \<forall>b\<in>B. x \<in> b) F"

  3337       by (auto intro!: eventually_Ball_finite)

  3338     with F(2) have "eventually (\<lambda>x. x \<in> U \<inter> (\<Inter>B)) F"

  3339       by eventually_elim auto

  3340     with F show "U \<inter> \<Inter>B \<noteq> {}"

  3341       by (intro notI) (simp add: eventually_False)

  3342   qed

  3343   ultimately have "U \<inter> \<Inter>Z \<noteq> {}"

  3344     using compact U unfolding compact_fip by blast

  3345   then obtain x where "x \<in> U" and x: "\<And>z. z \<in> Z \<Longrightarrow> x \<in> z"

  3346     by auto

  3347

  3348   have "\<And>P. eventually P (inf (nhds x) F) \<Longrightarrow> P \<noteq> bot"

  3349     unfolding eventually_inf eventually_nhds

  3350   proof safe

  3351     fix P Q R S

  3352     assume "eventually R F" "open S" "x \<in> S"

  3353     with open_inter_closure_eq_empty[of S "{x. R x}"] x[of "closure {x. R x}"]

  3354     have "S \<inter> {x. R x} \<noteq> {}" by (auto simp: Z_def)

  3355     moreover assume "Ball S Q" "\<forall>x. Q x \<and> R x \<longrightarrow> bot x"

  3356     ultimately show False by (auto simp: set_eq_iff)

  3357   qed

  3358   with x \<in> U show "\<exists>x\<in>U. inf (nhds x) F \<noteq> bot"

  3359     by (metis eventually_bot)

  3360 next

  3361   fix A

  3362   assume A: "\<forall>a\<in>A. closed a" "\<forall>B\<subseteq>A. finite B \<longrightarrow> U \<inter> \<Inter>B \<noteq> {}" "U \<inter> \<Inter>A = {}"

  3363   def P' \<equiv> "(\<lambda>a (x::'a). x \<in> a)"

  3364   then have inj_P': "\<And>A. inj_on P' A"

  3365     by (auto intro!: inj_onI simp: fun_eq_iff)

  3366   def F \<equiv> "filter_from_subbase (P'  insert U A)"

  3367   have "F \<noteq> bot"

  3368     unfolding F_def

  3369   proof (safe intro!: filter_from_subbase_not_bot)

  3370     fix X

  3371     assume "X \<subseteq> P'  insert U A" "finite X" "Inf X = bot"

  3372     then obtain B where "B \<subseteq> insert U A" "finite B" and B: "Inf (P'  B) = bot"

  3373       unfolding subset_image_iff by (auto intro: inj_P' finite_imageD simp del: Inf_image_eq)

  3374     with A(2)[THEN spec, of "B - {U}"] have "U \<inter> \<Inter>(B - {U}) \<noteq> {}"

  3375       by auto

  3376     with B show False

  3377       by (auto simp: P'_def fun_eq_iff)

  3378   qed

  3379   moreover have "eventually (\<lambda>x. x \<in> U) F"

  3380     unfolding F_def by (rule eventually_filter_from_subbaseI) (auto simp: P'_def)

  3381   moreover

  3382   assume "\<forall>F. F \<noteq> bot \<longrightarrow> eventually (\<lambda>x. x \<in> U) F \<longrightarrow> (\<exists>x\<in>U. inf (nhds x) F \<noteq> bot)"

  3383   ultimately obtain x where "x \<in> U" and x: "inf (nhds x) F \<noteq> bot"

  3384     by auto

  3385

  3386   {

  3387     fix V

  3388     assume "V \<in> A"

  3389     then have V: "eventually (\<lambda>x. x \<in> V) F"

  3390       by (auto simp add: F_def image_iff P'_def intro!: eventually_filter_from_subbaseI)

  3391     have "x \<in> closure V"

  3392       unfolding closure_iff_nhds_not_empty

  3393     proof (intro impI allI)

  3394       fix S A

  3395       assume "open S" "x \<in> S" "S \<subseteq> A"

  3396       then have "eventually (\<lambda>x. x \<in> A) (nhds x)"

  3397         by (auto simp: eventually_nhds)

  3398       with V have "eventually (\<lambda>x. x \<in> V \<inter> A) (inf (nhds x) F)"

  3399         by (auto simp: eventually_inf)

  3400       with x show "V \<inter> A \<noteq> {}"

  3401         by (auto simp del: Int_iff simp add: trivial_limit_def)

  3402     qed

  3403     then have "x \<in> V"

  3404       using V \<in> A A(1) by simp

  3405   }

  3406   with x\<in>U have "x \<in> U \<inter> \<Inter>A" by auto

  3407   with U \<inter> \<Inter>A = {} show False by auto

  3408 qed

  3409

  3410 definition "countably_compact U \<longleftrightarrow>

  3411     (\<forall>A. countable A \<longrightarrow> (\<forall>a\<in>A. open a) \<longrightarrow> U \<subseteq> \<Union>A \<longrightarrow> (\<exists>T\<subseteq>A. finite T \<and> U \<subseteq> \<Union>T))"

  3412

  3413 lemma countably_compactE:

  3414   assumes "countably_compact s" and "\<forall>t\<in>C. open t" and "s \<subseteq> \<Union>C" "countable C"

  3415   obtains C' where "C' \<subseteq> C" and "finite C'" and "s \<subseteq> \<Union>C'"

  3416   using assms unfolding countably_compact_def by metis

  3417

  3418 lemma countably_compactI:

  3419   assumes "\<And>C. \<forall>t\<in>C. open t \<Longrightarrow> s \<subseteq> \<Union>C \<Longrightarrow> countable C \<Longrightarrow> (\<exists>C'\<subseteq>C. finite C' \<and> s \<subseteq> \<Union>C')"

  3420   shows "countably_compact s"

  3421   using assms unfolding countably_compact_def by metis

  3422

  3423 lemma compact_imp_countably_compact: "compact U \<Longrightarrow> countably_compact U"

  3424   by (auto simp: compact_eq_heine_borel countably_compact_def)

  3425

  3426 lemma countably_compact_imp_compact:

  3427   assumes "countably_compact U"

  3428     and ccover: "countable B" "\<forall>b\<in>B. open b"

  3429     and basis: "\<And>T x. open T \<Longrightarrow> x \<in> T \<Longrightarrow> x \<in> U \<Longrightarrow> \<exists>b\<in>B. x \<in> b \<and> b \<inter> U \<subseteq> T"

  3430   shows "compact U"

  3431   using countably_compact U

  3432   unfolding compact_eq_heine_borel countably_compact_def

  3433 proof safe

  3434   fix A

  3435   assume A: "\<forall>a\<in>A. open a" "U \<subseteq> \<Union>A"

  3436   assume *: "\<forall>A. countable A \<longrightarrow> (\<forall>a\<in>A. open a) \<longrightarrow> U \<subseteq> \<Union>A \<longrightarrow> (\<exists>T\<subseteq>A. finite T \<and> U \<subseteq> \<Union>T)"

  3437

  3438   moreover def C \<equiv> "{b\<in>B. \<exists>a\<in>A. b \<inter> U \<subseteq> a}"

  3439   ultimately have "countable C" "\<forall>a\<in>C. open a"

  3440     unfolding C_def using ccover by auto

  3441   moreover

  3442   have "\<Union>A \<inter> U \<subseteq> \<Union>C"

  3443   proof safe

  3444     fix x a

  3445     assume "x \<in> U" "x \<in> a" "a \<in> A"

  3446     with basis[of a x] A obtain b where "b \<in> B" "x \<in> b" "b \<inter> U \<subseteq> a"

  3447       by blast

  3448     with a \<in> A show "x \<in> \<Union>C"

  3449       unfolding C_def by auto

  3450   qed

  3451   then have "U \<subseteq> \<Union>C" using U \<subseteq> \<Union>A by auto

  3452   ultimately obtain T where T: "T\<subseteq>C" "finite T" "U \<subseteq> \<Union>T"

  3453     using * by metis

  3454   then have "\<forall>t\<in>T. \<exists>a\<in>A. t \<inter> U \<subseteq> a"

  3455     by (auto simp: C_def)

  3456   then obtain f where "\<forall>t\<in>T. f t \<in> A \<and> t \<inter> U \<subseteq> f t"

  3457     unfolding bchoice_iff Bex_def ..

  3458   with T show "\<exists>T\<subseteq>A. finite T \<and> U \<subseteq> \<Union>T"

  3459     unfolding C_def by (intro exI[of _ "fT"]) fastforce

  3460 qed

  3461

  3462 lemma countably_compact_imp_compact_second_countable:

  3463   "countably_compact U \<Longrightarrow> compact (U :: 'a :: second_countable_topology set)"

  3464 proof (rule countably_compact_imp_compact)

  3465   fix T and x :: 'a

  3466   assume "open T" "x \<in> T"

  3467   from topological_basisE[OF is_basis this] obtain b where

  3468     "b \<in> (SOME B. countable B \<and> topological_basis B)" "x \<in> b" "b \<subseteq> T" .

  3469   then show "\<exists>b\<in>SOME B. countable B \<and> topological_basis B. x \<in> b \<and> b \<inter> U \<subseteq> T"

  3470     by blast

  3471 qed (insert countable_basis topological_basis_open[OF is_basis], auto)

  3472

  3473 lemma countably_compact_eq_compact:

  3474   "countably_compact U \<longleftrightarrow> compact (U :: 'a :: second_countable_topology set)"

  3475   using countably_compact_imp_compact_second_countable compact_imp_countably_compact by blast

  3476

  3477 subsubsection{* Sequential compactness *}

  3478

  3479 definition seq_compact :: "'a::topological_space set \<Rightarrow> bool"

  3480   where "seq_compact S \<longleftrightarrow>

  3481     (\<forall>f. (\<forall>n. f n \<in> S) \<longrightarrow> (\<exists>l\<in>S. \<exists>r. subseq r \<and> ((f \<circ> r) ---> l) sequentially))"

  3482

  3483 lemma seq_compactI:

  3484   assumes "\<And>f. \<forall>n. f n \<in> S \<Longrightarrow> \<exists>l\<in>S. \<exists>r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"

  3485   shows "seq_compact S"

  3486   unfolding seq_compact_def using assms by fast

  3487

  3488 lemma seq_compactE:

  3489   assumes "seq_compact S" "\<forall>n. f n \<in> S"

  3490   obtains l r where "l \<in> S" "subseq r" "((f \<circ> r) ---> l) sequentially"

  3491   using assms unfolding seq_compact_def by fast

  3492

  3493 lemma closed_sequentially: (* TODO: move upwards *)

  3494   assumes "closed s" and "\<forall>n. f n \<in> s" and "f ----> l"

  3495   shows "l \<in> s"

  3496 proof (rule ccontr)

  3497   assume "l \<notin> s"

  3498   with closed s and f ----> l have "eventually (\<lambda>n. f n \<in> - s) sequentially"

  3499     by (fast intro: topological_tendstoD)

  3500   with \<forall>n. f n \<in> s show "False"

  3501     by simp

  3502 qed

  3503

  3504 lemma seq_compact_inter_closed:

  3505   assumes "seq_compact s" and "closed t"

  3506   shows "seq_compact (s \<inter> t)"

  3507 proof (rule seq_compactI)

  3508   fix f assume "\<forall>n::nat. f n \<in> s \<inter> t"

  3509   hence "\<forall>n. f n \<in> s" and "\<forall>n. f n \<in> t"

  3510     by simp_all

  3511   from seq_compact s and \<forall>n. f n \<in> s

  3512   obtain l r where "l \<in> s" and r: "subseq r" and l: "(f \<circ> r) ----> l"

  3513     by (rule seq_compactE)

  3514   from \<forall>n. f n \<in> t have "\<forall>n. (f \<circ> r) n \<in> t"

  3515     by simp

  3516   from closed t and this and l have "l \<in> t"

  3517     by (rule closed_sequentially)

  3518   with l \<in> s and r and l show "\<exists>l\<in>s \<inter> t. \<exists>r. subseq r \<and> (f \<circ> r) ----> l"

  3519     by fast

  3520 qed

  3521

  3522 lemma seq_compact_closed_subset:

  3523   assumes "closed s" and "s \<subseteq> t" and "seq_compact t"

  3524   shows "seq_compact s"

  3525   using assms seq_compact_inter_closed [of t s] by (simp add: Int_absorb1)

  3526

  3527 lemma seq_compact_imp_countably_compact:

  3528   fixes U :: "'a :: first_countable_topology set"

  3529   assumes "seq_compact U"

  3530   shows "countably_compact U"

  3531 proof (safe intro!: countably_compactI)

  3532   fix A

  3533   assume A: "\<forall>a\<in>A. open a" "U \<subseteq> \<Union>A" "countable A"

  3534   have subseq: "\<And>X. range X \<subseteq> U \<Longrightarrow> \<exists>r x. x \<in> U \<and> subseq r \<and> (X \<circ> r) ----> x"

  3535     using seq_compact U by (fastforce simp: seq_compact_def subset_eq)

  3536   show "\<exists>T\<subseteq>A. finite T \<and> U \<subseteq> \<Union>T"

  3537   proof cases

  3538     assume "finite A"

  3539     with A show ?thesis by auto

  3540   next

  3541     assume "infinite A"

  3542     then have "A \<noteq> {}" by auto

  3543     show ?thesis

  3544     proof (rule ccontr)

  3545       assume "\<not> (\<exists>T\<subseteq>A. finite T \<and> U \<subseteq> \<Union>T)"

  3546       then have "\<forall>T. \<exists>x. T \<subseteq> A \<and> finite T \<longrightarrow> (x \<in> U - \<Union>T)"

  3547         by auto

  3548       then obtain X' where T: "\<And>T. T \<subseteq> A \<Longrightarrow> finite T \<Longrightarrow> X' T \<in> U - \<Union>T"

  3549         by metis

  3550       def X \<equiv> "\<lambda>n. X' (from_nat_into A  {.. n})"

  3551       have X: "\<And>n. X n \<in> U - (\<Union>i\<le>n. from_nat_into A i)"

  3552         using A \<noteq> {} unfolding X_def SUP_def by (intro T) (auto intro: from_nat_into)

  3553       then have "range X \<subseteq> U"

  3554         by auto

  3555       with subseq[of X] obtain r x where "x \<in> U" and r: "subseq r" "(X \<circ> r) ----> x"

  3556         by auto

  3557       from x\<in>U U \<subseteq> \<Union>A from_nat_into_surj[OF countable A]

  3558       obtain n where "x \<in> from_nat_into A n" by auto

  3559       with r(2) A(1) from_nat_into[OF A \<noteq> {}, of n]

  3560       have "eventually (\<lambda>i. X (r i) \<in> from_nat_into A n) sequentially"

  3561         unfolding tendsto_def by (auto simp: comp_def)

  3562       then obtain N where "\<And>i. N \<le> i \<Longrightarrow> X (r i) \<in> from_nat_into A n"

  3563         by (auto simp: eventually_sequentially)

  3564       moreover from X have "\<And>i. n \<le> r i \<Longrightarrow> X (r i) \<notin> from_nat_into A n"

  3565         by auto

  3566       moreover from subseq r[THEN seq_suble, of "max n N"] have "\<exists>i. n \<le> r i \<and> N \<le> i"

  3567         by (auto intro!: exI[of _ "max n N"])

  3568       ultimately show False

  3569         by auto

  3570     qed

  3571   qed

  3572 qed

  3573

  3574 lemma compact_imp_seq_compact:

  3575   fixes U :: "'a :: first_countable_topology set"

  3576   assumes "compact U"

  3577   shows "seq_compact U"

  3578   unfolding seq_compact_def

  3579 proof safe

  3580   fix X :: "nat \<Rightarrow> 'a"

  3581   assume "\<forall>n. X n \<in> U"

  3582   then have "eventually (\<lambda>x. x \<in> U) (filtermap X sequentially)"

  3583     by (auto simp: eventually_filtermap)

  3584   moreover

  3585   have "filtermap X sequentially \<noteq> bot"

  3586     by (simp add: trivial_limit_def eventually_filtermap)

  3587   ultimately

  3588   obtain x where "x \<in> U" and x: "inf (nhds x) (filtermap X sequentially) \<noteq> bot" (is "?F \<noteq> _")

  3589     using compact U by (auto simp: compact_filter)

  3590

  3591   from countable_basis_at_decseq[of x]

  3592   obtain A where A:

  3593       "\<And>i. open (A i)"

  3594       "\<And>i. x \<in> A i"

  3595       "\<And>S. open S \<Longrightarrow> x \<in> S \<Longrightarrow> eventually (\<lambda>i. A i \<subseteq> S) sequentially"

  3596     by blast

  3597   def s \<equiv> "\<lambda>n i. SOME j. i < j \<and> X j \<in> A (Suc n)"

  3598   {

  3599     fix n i

  3600     have "\<exists>a. i < a \<and> X a \<in> A (Suc n)"

  3601     proof (rule ccontr)

  3602       assume "\<not> (\<exists>a>i. X a \<in> A (Suc n))"

  3603       then have "\<And>a. Suc i \<le> a \<Longrightarrow> X a \<notin> A (Suc n)"

  3604         by auto

  3605       then have "eventually (\<lambda>x. x \<notin> A (Suc n)) (filtermap X sequentially)"

  3606         by (auto simp: eventually_filtermap eventually_sequentially)

  3607       moreover have "eventually (\<lambda>x. x \<in> A (Suc n)) (nhds x)"

  3608         using A(1,2)[of "Suc n"] by (auto simp: eventually_nhds)

  3609       ultimately have "eventually (\<lambda>x. False) ?F"

  3610         by (auto simp add: eventually_inf)

  3611       with x show False

  3612         by (simp add: eventually_False)

  3613     qed

  3614     then have "i < s n i" "X (s n i) \<in> A (Suc n)"

  3615       unfolding s_def by (auto intro: someI2_ex)

  3616   }

  3617   note s = this

  3618   def r \<equiv> "rec_nat (s 0 0) s"

  3619   have "subseq r"

  3620     by (auto simp: r_def s subseq_Suc_iff)

  3621   moreover

  3622   have "(\<lambda>n. X (r n)) ----> x"

  3623   proof (rule topological_tendstoI)

  3624     fix S

  3625     assume "open S" "x \<in> S"

  3626     with A(3) have "eventually (\<lambda>i. A i \<subseteq> S) sequentially"

  3627       by auto

  3628     moreover

  3629     {

  3630       fix i

  3631       assume "Suc 0 \<le> i"

  3632       then have "X (r i) \<in> A i"

  3633         by (cases i) (simp_all add: r_def s)

  3634     }

  3635     then have "eventually (\<lambda>i. X (r i) \<in> A i) sequentially"

  3636       by (auto simp: eventually_sequentially)

  3637     ultimately show "eventually (\<lambda>i. X (r i) \<in> S) sequentially"

  3638       by eventually_elim auto

  3639   qed

  3640   ultimately show "\<exists>x \<in> U. \<exists>r. subseq r \<and> (X \<circ> r) ----> x"

  3641     using x \<in> U by (auto simp: convergent_def comp_def)

  3642 qed

  3643

  3644 lemma countably_compact_imp_acc_point:

  3645   assumes "countably_compact s"

  3646     and "countable t"

  3647     and "infinite t"

  3648     and "t \<subseteq> s"

  3649   shows "\<exists>x\<in>s. \<forall>U. x\<in>U \<and> open U \<longrightarrow> infinite (U \<inter> t)"

  3650 proof (rule ccontr)

  3651   def C \<equiv> "(\<lambda>F. interior (F \<union> (- t)))  {F. finite F \<and> F \<subseteq> t }"

  3652   note countably_compact s

  3653   moreover have "\<forall>t\<in>C. open t"

  3654     by (auto simp: C_def)

  3655   moreover

  3656   assume "\<not> (\<exists>x\<in>s. \<forall>U. x\<in>U \<and> open U \<longrightarrow> infinite (U \<inter> t))"

  3657   then have s: "\<And>x. x \<in> s \<Longrightarrow> \<exists>U. x\<in>U \<and> open U \<and> finite (U \<inter> t)" by metis

  3658   have "s \<subseteq> \<Union>C"

  3659     using t \<subseteq> s

  3660     unfolding C_def Union_image_eq

  3661     apply (safe dest!: s)

  3662     apply (rule_tac a="U \<inter> t" in UN_I)

  3663     apply (auto intro!: interiorI simp add: finite_subset)

  3664     done

  3665   moreover

  3666   from countable t have "countable C"

  3667     unfolding C_def by (auto intro: countable_Collect_finite_subset)

  3668   ultimately

  3669   obtain D where "D \<subseteq> C" "finite D" "s \<subseteq> \<Union>D"

  3670     by (rule countably_compactE)

  3671   then obtain E where E: "E \<subseteq> {F. finite F \<and> F \<subseteq> t }" "finite E"

  3672     and s: "s \<subseteq> (\<Union>F\<in>E. interior (F \<union> (- t)))"

  3673     by (metis (lifting) Union_image_eq finite_subset_image C_def)

  3674   from s t \<subseteq> s have "t \<subseteq> \<Union>E"

  3675     using interior_subset by blast

  3676   moreover have "finite (\<Union>E)"

  3677     using E by auto

  3678   ultimately show False using infinite t

  3679     by (auto simp: finite_subset)

  3680 qed

  3681

  3682 lemma countable_acc_point_imp_seq_compact:

  3683   fixes s :: "'a::first_countable_topology set"

  3684   assumes "\<forall>t. infinite t \<and> countable t \<and> t \<subseteq> s \<longrightarrow>

  3685     (\<exists>x\<in>s. \<forall>U. x\<in>U \<and> open U \<longrightarrow> infinite (U \<inter> t))"

  3686   shows "seq_compact s"

  3687 proof -

  3688   {

  3689     fix f :: "nat \<Rightarrow> 'a"

  3690     assume f: "\<forall>n. f n \<in> s"

  3691     have "\<exists>l\<in>s. \<exists>r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"

  3692     proof (cases "finite (range f)")

  3693       case True

  3694       obtain l where "infinite {n. f n = f l}"

  3695         using pigeonhole_infinite[OF _ True] by auto

  3696       then obtain r where "subseq r" and fr: "\<forall>n. f (r n) = f l"

  3697         using infinite_enumerate by blast

  3698       then have "subseq r \<and> (f \<circ> r) ----> f l"

  3699         by (simp add: fr tendsto_const o_def)

  3700       with f show "\<exists>l\<in>s. \<exists>r. subseq r \<and> (f \<circ> r) ----> l"

  3701         by auto

  3702     next

  3703       case False

  3704       with f assms have "\<exists>x\<in>s. \<forall>U. x\<in>U \<and> open U \<longrightarrow> infinite (U \<inter> range f)"

  3705         by auto

  3706       then obtain l where "l \<in> s" "\<forall>U. l\<in>U \<and> open U \<longrightarrow> infinite (U \<inter> range f)" ..

  3707       from this(2) have "\<exists>r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"

  3708         using acc_point_range_imp_convergent_subsequence[of l f] by auto

  3709       with l \<in> s show "\<exists>l\<in>s. \<exists>r. subseq r \<and> ((f \<circ> r) ---> l) sequentially" ..

  3710     qed

  3711   }

  3712   then show ?thesis

  3713     unfolding seq_compact_def by auto

  3714 qed

  3715

  3716 lemma seq_compact_eq_countably_compact:

  3717   fixes U :: "'a :: first_countable_topology set"

  3718   shows "seq_compact U \<longleftrightarrow> countably_compact U"

  3719   using

  3720     countable_acc_point_imp_seq_compact

  3721     countably_compact_imp_acc_point

  3722     seq_compact_imp_countably_compact

  3723   by metis

  3724

  3725 lemma seq_compact_eq_acc_point:

  3726   fixes s :: "'a :: first_countable_topology set"

  3727   shows "seq_compact s \<longleftrightarrow>

  3728     (\<forall>t. infinite t \<and> countable t \<and> t \<subseteq> s --> (\<exists>x\<in>s. \<forall>U. x\<in>U \<and> open U \<longrightarrow> infinite (U \<inter> t)))"

  3729   using

  3730     countable_acc_point_imp_seq_compact[of s]

  3731     countably_compact_imp_acc_point[of s]

  3732     seq_compact_imp_countably_compact[of s]

  3733   by metis

  3734

  3735 lemma seq_compact_eq_compact:

  3736   fixes U :: "'a :: second_countable_topology set"

  3737   shows "seq_compact U \<longleftrightarrow> compact U"

  3738   using seq_compact_eq_countably_compact countably_compact_eq_compact by blast

  3739

  3740 lemma bolzano_weierstrass_imp_seq_compact:

  3741   fixes s :: "'a::{t1_space, first_countable_topology} set"

  3742   shows "\<forall>t. infinite t \<and> t \<subseteq> s --> (\<exists>x \<in> s. x islimpt t) \<Longrightarrow> seq_compact s"

  3743   by (rule countable_acc_point_imp_seq_compact) (metis islimpt_eq_acc_point)

  3744

  3745 subsubsection{* Total boundedness *}

  3746

  3747 lemma cauchy_def: "Cauchy s \<longleftrightarrow> (\<forall>e>0. \<exists>N. \<forall>m n. m \<ge> N \<and> n \<ge> N --> dist(s m)(s n) < e)"

  3748   unfolding Cauchy_def by metis

  3749

  3750 fun helper_1 :: "('a::metric_space set) \<Rightarrow> real \<Rightarrow> nat \<Rightarrow> 'a"

  3751 where

  3752   "helper_1 s e n = (SOME y::'a. y \<in> s \<and> (\<forall>m<n. \<not> (dist (helper_1 s e m) y < e)))"

  3753 declare helper_1.simps[simp del]

  3754

  3755 lemma seq_compact_imp_totally_bounded:

  3756   assumes "seq_compact s"

  3757   shows "\<forall>e>0. \<exists>k. finite k \<and> k \<subseteq> s \<and> s \<subseteq> (\<Union>((\<lambda>x. ball x e)  k))"

  3758 proof (rule, rule, rule ccontr)

  3759   fix e::real

  3760   assume "e > 0"

  3761   assume assm: "\<not> (\<exists>k. finite k \<and> k \<subseteq> s \<and> s \<subseteq> \<Union>((\<lambda>x. ball x e)  k))"

  3762   def x \<equiv> "helper_1 s e"

  3763   {

  3764     fix n

  3765     have "x n \<in> s \<and> (\<forall>m<n. \<not> dist (x m) (x n) < e)"

  3766     proof (induct n rule: nat_less_induct)

  3767       fix n

  3768       def Q \<equiv> "(\<lambda>y. y \<in> s \<and> (\<forall>m<n. \<not> dist (x m) y < e))"

  3769       assume as: "\<forall>m<n. x m \<in> s \<and> (\<forall>ma<m. \<not> dist (x ma) (x m) < e)"

  3770       have "\<not> s \<subseteq> (\<Union>x\<in>x  {0..<n}. ball x e)"

  3771         using assm

  3772         apply simp

  3773         apply (erule_tac x="x  {0 ..< n}" in allE)

  3774         using as

  3775         apply auto

  3776         done

  3777       then obtain z where z:"z\<in>s" "z \<notin> (\<Union>x\<in>x  {0..<n}. ball x e)"

  3778         unfolding subset_eq by auto

  3779       have "Q (x n)"

  3780         unfolding x_def and helper_1.simps[of s e n]

  3781         apply (rule someI2[where a=z])

  3782         unfolding x_def[symmetric] and Q_def

  3783         using z

  3784         apply auto

  3785         done

  3786       then show "x n \<in> s \<and> (\<forall>m<n. \<not> dist (x m) (x n) < e)"

  3787         unfolding Q_def by auto

  3788     qed

  3789   }

  3790   then have "\<forall>n::nat. x n \<in> s" and x:"\<forall>n. \<forall>m < n. \<not> (dist (x m) (x n) < e)"

  3791     by blast+

  3792   then obtain l r where "l\<in>s" and r:"subseq r" and "((x \<circ> r) ---> l) sequentially"

  3793     using assms(1)[unfolded seq_compact_def, THEN spec[where x=x]] by auto

  3794   from this(3) have "Cauchy (x \<circ> r)"

  3795     using LIMSEQ_imp_Cauchy by auto

  3796   then obtain N::nat where N:"\<forall>m n. N \<le> m \<and> N \<le> n \<longrightarrow> dist ((x \<circ> r) m) ((x \<circ> r) n) < e"

  3797     unfolding cauchy_def using e>0 by auto

  3798   show False

  3799     using N[THEN spec[where x=N], THEN spec[where x="N+1"]]

  3800     using r[unfolded subseq_def, THEN spec[where x=N], THEN spec[where x="N+1"]]

  3801     using x[THEN spec[where x="r (N+1)"], THEN spec[where x="r (N)"]]

  3802     by auto

  3803 qed

  3804

  3805 subsubsection{* Heine-Borel theorem *}

  3806

  3807 lemma seq_compact_imp_heine_borel:

  3808   fixes s :: "'a :: metric_space set"

  3809   assumes "seq_compact s"

  3810   shows "compact s"

  3811 proof -

  3812   from seq_compact_imp_totally_bounded[OF seq_compact s]

  3813   obtain f where f: "\<forall>e>0. finite (f e) \<and> f e \<subseteq> s \<and> s \<subseteq> \<Union>((\<lambda>x. ball x e)  f e)"

  3814     unfolding choice_iff' ..

  3815   def K \<equiv> "(\<lambda>(x, r). ball x r)  ((\<Union>e \<in> \<rat> \<inter> {0 <..}. f e) \<times> \<rat>)"

  3816   have "countably_compact s"

  3817     using seq_compact s by (rule seq_compact_imp_countably_compact)

  3818   then show "compact s"

  3819   proof (rule countably_compact_imp_compact)

  3820     show "countable K"

  3821       unfolding K_def using f

  3822       by (auto intro: countable_finite countable_subset countable_rat

  3823                intro!: countable_image countable_SIGMA countable_UN)

  3824     show "\<forall>b\<in>K. open b" by (auto simp: K_def)

  3825   next

  3826     fix T x

  3827     assume T: "open T" "x \<in> T" and x: "x \<in> s"

  3828     from openE[OF T] obtain e where "0 < e" "ball x e \<subseteq> T"

  3829       by auto

  3830     then have "0 < e / 2" "ball x (e / 2) \<subseteq> T"

  3831       by auto

  3832     from Rats_dense_in_real[OF 0 < e / 2] obtain r where "r \<in> \<rat>" "0 < r" "r < e / 2"

  3833       by auto

  3834     from f[rule_format, of r] 0 < r x \<in> s obtain k where "k \<in> f r" "x \<in> ball k r"

  3835       unfolding Union_image_eq by auto

  3836     from r \<in> \<rat> 0 < r k \<in> f r have "ball k r \<in> K"

  3837       by (auto simp: K_def)

  3838     then show "\<exists>b\<in>K. x \<in> b \<and> b \<inter> s \<subseteq> T"

  3839     proof (rule bexI[rotated], safe)

  3840       fix y

  3841       assume "y \<in> ball k r"

  3842       with r < e / 2 x \<in> ball k r have "dist x y < e"

  3843         by (intro dist_double[where x = k and d=e]) (auto simp: dist_commute)

  3844       with ball x e \<subseteq> T show "y \<in> T"

  3845         by auto

  3846     next

  3847       show "x \<in> ball k r" by fact

  3848     qed

  3849   qed

  3850 qed

  3851

  3852 lemma compact_eq_seq_compact_metric:

  3853   "compact (s :: 'a::metric_space set) \<longleftrightarrow> seq_compact s"

  3854   using compact_imp_seq_compact seq_compact_imp_heine_borel by blast

  3855

  3856 lemma compact_def:

  3857   "compact (S :: 'a::metric_space set) \<longleftrightarrow>

  3858    (\<forall>f. (\<forall>n. f n \<in> S) \<longrightarrow> (\<exists>l\<in>S. \<exists>r. subseq r \<and> (f \<circ> r) ----> l))"

  3859   unfolding compact_eq_seq_compact_metric seq_compact_def by auto

  3860

  3861 subsubsection {* Complete the chain of compactness variants *}

  3862

  3863 lemma compact_eq_bolzano_weierstrass:

  3864   fixes s :: "'a::metric_space set"

  3865   shows "compact s \<longleftrightarrow> (\<forall>t. infinite t \<and> t \<subseteq> s --> (\<exists>x \<in> s. x islimpt t))"

  3866   (is "?lhs = ?rhs")

  3867 proof

  3868   assume ?lhs

  3869   then show ?rhs

  3870     using heine_borel_imp_bolzano_weierstrass[of s] by auto

  3871 next

  3872   assume ?rhs

  3873   then show ?lhs

  3874     unfolding compact_eq_seq_compact_metric by (rule bolzano_weierstrass_imp_seq_compact)

  3875 qed

  3876

  3877 lemma bolzano_weierstrass_imp_bounded:

  3878   "\<forall>t. infinite t \<and> t \<subseteq> s \<longrightarrow> (\<exists>x \<in> s. x islimpt t) \<Longrightarrow> bounded s"

  3879   using compact_imp_bounded unfolding compact_eq_bolzano_weierstrass .

  3880

  3881 subsection {* Metric spaces with the Heine-Borel property *}

  3882

  3883 text {*

  3884   A metric space (or topological vector space) is said to have the

  3885   Heine-Borel property if every closed and bounded subset is compact.

  3886 *}

  3887

  3888 class heine_borel = metric_space +

  3889   assumes bounded_imp_convergent_subsequence:

  3890     "bounded (range f) \<Longrightarrow> \<exists>l r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"

  3891

  3892 lemma bounded_closed_imp_seq_compact:

  3893   fixes s::"'a::heine_borel set"

  3894   assumes "bounded s"

  3895     and "closed s"

  3896   shows "seq_compact s"

  3897 proof (unfold seq_compact_def, clarify)

  3898   fix f :: "nat \<Rightarrow> 'a"

  3899   assume f: "\<forall>n. f n \<in> s"

  3900   with bounded s have "bounded (range f)"

  3901     by (auto intro: bounded_subset)

  3902   obtain l r where r: "subseq r" and l: "((f \<circ> r) ---> l) sequentially"

  3903     using bounded_imp_convergent_subsequence [OF bounded (range f)] by auto

  3904   from f have fr: "\<forall>n. (f \<circ> r) n \<in> s"

  3905     by simp

  3906   have "l \<in> s" using closed s fr l

  3907     by (rule closed_sequentially)

  3908   show "\<exists>l\<in>s. \<exists>r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"

  3909     using l \<in> s r l by blast

  3910 qed

  3911

  3912 lemma compact_eq_bounded_closed:

  3913   fixes s :: "'a::heine_borel set"

  3914   shows "compact s \<longleftrightarrow> bounded s \<and> closed s"

  3915   (is "?lhs = ?rhs")

  3916 proof

  3917   assume ?lhs

  3918   then show ?rhs

  3919     using compact_imp_closed compact_imp_bounded

  3920     by blast

  3921 next

  3922   assume ?rhs

  3923   then show ?lhs

  3924     using bounded_closed_imp_seq_compact[of s]

  3925     unfolding compact_eq_seq_compact_metric

  3926     by auto

  3927 qed

  3928

  3929 (* TODO: is this lemma necessary? *)

  3930 lemma bounded_increasing_convergent:

  3931   fixes s :: "nat \<Rightarrow> real"

  3932   shows "bounded {s n| n. True} \<Longrightarrow> \<forall>n. s n \<le> s (Suc n) \<Longrightarrow> \<exists>l. s ----> l"

  3933   using Bseq_mono_convergent[of s] incseq_Suc_iff[of s]

  3934   by (auto simp: image_def Bseq_eq_bounded convergent_def incseq_def)

  3935

  3936 instance real :: heine_borel

  3937 proof

  3938   fix f :: "nat \<Rightarrow> real"

  3939   assume f: "bounded (range f)"

  3940   obtain r where r: "subseq r" "monoseq (f \<circ> r)"

  3941     unfolding comp_def by (metis seq_monosub)

  3942   then have "Bseq (f \<circ> r)"

  3943     unfolding Bseq_eq_bounded using f by (auto intro: bounded_subset)

  3944   with r show "\<exists>l r. subseq r \<and> (f \<circ> r) ----> l"

  3945     using Bseq_monoseq_convergent[of "f \<circ> r"] by (auto simp: convergent_def)

  3946 qed

  3947

  3948 lemma compact_lemma:

  3949   fixes f :: "nat \<Rightarrow> 'a::euclidean_space"

  3950   assumes "bounded (range f)"

  3951   shows "\<forall>d\<subseteq>Basis. \<exists>l::'a. \<exists> r.

  3952     subseq r \<and> (\<forall>e>0. eventually (\<lambda>n. \<forall>i\<in>d. dist (f (r n) \<bullet> i) (l \<bullet> i) < e) sequentially)"

  3953 proof safe

  3954   fix d :: "'a set"

  3955   assume d: "d \<subseteq> Basis"

  3956   with finite_Basis have "finite d"

  3957     by (blast intro: finite_subset)

  3958   from this d show "\<exists>l::'a. \<exists>r. subseq r \<and>

  3959     (\<forall>e>0. eventually (\<lambda>n. \<forall>i\<in>d. dist (f (r n) \<bullet> i) (l \<bullet> i) < e) sequentially)"

  3960   proof (induct d)

  3961     case empty

  3962     then show ?case

  3963       unfolding subseq_def by auto

  3964   next

  3965     case (insert k d)

  3966     have k[intro]: "k \<in> Basis"

  3967       using insert by auto

  3968     have s': "bounded ((\<lambda>x. x \<bullet> k)  range f)"

  3969       using bounded (range f)

  3970       by (auto intro!: bounded_linear_image bounded_linear_inner_left)

  3971     obtain l1::"'a" and r1 where r1: "subseq r1"

  3972       and lr1: "\<forall>e > 0. eventually (\<lambda>n. \<forall>i\<in>d. dist (f (r1 n) \<bullet> i) (l1 \<bullet> i) < e) sequentially"

  3973       using insert(3) using insert(4) by auto

  3974     have f': "\<forall>n. f (r1 n) \<bullet> k \<in> (\<lambda>x. x \<bullet> k)  range f"

  3975       by simp

  3976     have "bounded (range (\<lambda>i. f (r1 i) \<bullet> k))"

  3977       by (metis (lifting) bounded_subset f' image_subsetI s')

  3978     then obtain l2 r2 where r2:"subseq r2" and lr2:"((\<lambda>i. f (r1 (r2 i)) \<bullet> k) ---> l2) sequentially"

  3979       using bounded_imp_convergent_subsequence[of "\<lambda>i. f (r1 i) \<bullet> k"]

  3980       by (auto simp: o_def)

  3981     def r \<equiv> "r1 \<circ> r2"

  3982     have r:"subseq r"

  3983       using r1 and r2 unfolding r_def o_def subseq_def by auto

  3984     moreover

  3985     def l \<equiv> "(\<Sum>i\<in>Basis. (if i = k then l2 else l1\<bullet>i) *\<^sub>R i)::'a"

  3986     {

  3987       fix e::real

  3988       assume "e > 0"

  3989       from lr1 e > 0 have N1: "eventually (\<lambda>n. \<forall>i\<in>d. dist (f (r1 n) \<bullet> i) (l1 \<bullet> i) < e) sequentially"

  3990         by blast

  3991       from lr2 e > 0 have N2:"eventually (\<lambda>n. dist (f (r1 (r2 n)) \<bullet> k) l2 < e) sequentially"

  3992         by (rule tendstoD)

  3993       from r2 N1 have N1': "eventually (\<lambda>n. \<forall>i\<in>d. dist (f (r1 (r2 n)) \<bullet> i) (l1 \<bullet> i) < e) sequentially"

  3994         by (rule eventually_subseq)

  3995       have "eventually (\<lambda>n. \<forall>i\<in>(insert k d). dist (f (r n) \<bullet> i) (l \<bullet> i) < e) sequentially"

  3996         using N1' N2

  3997         by eventually_elim (insert insert.prems, auto simp: l_def r_def o_def)

  3998     }

  3999     ultimately show ?case by auto

  4000   qed

  4001 qed

  4002

  4003 instance euclidean_space \<subseteq> heine_borel

  4004 proof

  4005   fix f :: "nat \<Rightarrow> 'a"

  4006   assume f: "bounded (range f)"

  4007   then obtain l::'a and r where r: "subseq r"

  4008     and l: "\<forall>e>0. eventually (\<lambda>n. \<forall>i\<in>Basis. dist (f (r n) \<bullet> i) (l \<bullet> i) < e) sequentially"

  4009     using compact_lemma [OF f] by blast

  4010   {

  4011     fix e::real

  4012     assume "e > 0"

  4013     hence "e / real_of_nat DIM('a) > 0" by (simp add: DIM_positive)

  4014     with l have "eventually (\<lambda>n. \<forall>i\<in>Basis. dist (f (r n) \<bullet> i) (l \<bullet> i) < e / (real_of_nat DIM('a))) sequentially"

  4015       by simp

  4016     moreover

  4017     {

  4018       fix n

  4019       assume n: "\<forall>i\<in>Basis. dist (f (r n) \<bullet> i) (l \<bullet> i) < e / (real_of_nat DIM('a))"

  4020       have "dist (f (r n)) l \<le> (\<Sum>i\<in>Basis. dist (f (r n) \<bullet> i) (l \<bullet> i))"

  4021         apply (subst euclidean_dist_l2)

  4022         using zero_le_dist

  4023         apply (rule setL2_le_setsum)

  4024         done

  4025       also have "\<dots> < (\<Sum>i\<in>(Basis::'a set). e / (real_of_nat DIM('a)))"

  4026         apply (rule setsum_strict_mono)

  4027         using n

  4028         apply auto

  4029         done

  4030       finally have "dist (f (r n)) l < e"

  4031         by auto

  4032     }

  4033     ultimately have "eventually (\<lambda>n. dist (f (r n)) l < e) sequentially"

  4034       by (rule eventually_elim1)

  4035   }

  4036   then have *: "((f \<circ> r) ---> l) sequentially"

  4037     unfolding o_def tendsto_iff by simp

  4038   with r show "\<exists>l r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"

  4039     by auto

  4040 qed

  4041

  4042 lemma bounded_fst: "bounded s \<Longrightarrow> bounded (fst  s)"

  4043   unfolding bounded_def

  4044   by (metis (erased, hide_lams) dist_fst_le image_iff order_trans)

  4045

  4046 lemma bounded_snd: "bounded s \<Longrightarrow> bounded (snd  s)"

  4047   unfolding bounded_def

  4048   by (metis (no_types, hide_lams) dist_snd_le image_iff order.trans)

  4049

  4050 instance prod :: (heine_borel, heine_borel) heine_borel

  4051 proof

  4052   fix f :: "nat \<Rightarrow> 'a \<times> 'b"

  4053   assume f: "bounded (range f)"

  4054   then have "bounded (fst  range f)"

  4055     by (rule bounded_fst)

  4056   then have s1: "bounded (range (fst \<circ> f))"

  4057     by (simp add: image_comp)

  4058   obtain l1 r1 where r1: "subseq r1" and l1: "(\<lambda>n. fst (f (r1 n))) ----> l1"

  4059     using bounded_imp_convergent_subsequence [OF s1] unfolding o_def by fast

  4060   from f have s2: "bounded (range (snd \<circ> f \<circ> r1))"

  4061     by (auto simp add: image_comp intro: bounded_snd bounded_subset)

  4062   obtain l2 r2 where r2: "subseq r2" and l2: "((\<lambda>n. snd (f (r1 (r2 n)))) ---> l2) sequentially"

  4063     using bounded_imp_convergent_subsequence [OF s2]

  4064     unfolding o_def by fast

  4065   have l1': "((\<lambda>n. fst (f (r1 (r2 n)))) ---> l1) sequentially"

  4066     using LIMSEQ_subseq_LIMSEQ [OF l1 r2] unfolding o_def .

  4067   have l: "((f \<circ> (r1 \<circ> r2)) ---> (l1, l2)) sequentially"

  4068     using tendsto_Pair [OF l1' l2] unfolding o_def by simp

  4069   have r: "subseq (r1 \<circ> r2)"

  4070     using r1 r2 unfolding subseq_def by simp

  4071   show "\<exists>l r. subseq r \<and> ((f \<circ> r) ---> l) sequentially"

  4072     using l r by fast

  4073 qed

  4074

  4075 subsubsection {* Completeness *}

  4076

  4077 definition complete :: "'a::metric_space set \<Rightarrow> bool"

  4078   where "complete s \<longleftrightarrow> (\<forall>f. (\<forall>n. f n \<in> s) \<and> Cauchy f \<longrightarrow> (\<exists>l\<in>s. f ----> l))"

  4079

  4080 lemma completeI:

  4081   assumes "\<And>f. \<forall>n. f n \<in> s \<Longrightarrow> Cauchy f \<Longrightarrow> \<exists>l\<in>s. f ----> l"

  4082   shows "complete s"

  4083   using assms unfolding complete_def by fast

  4084

  4085 lemma completeE:

  4086   assumes "complete s" and "\<forall>n. f n \<in> s" and "Cauchy f"

  4087   obtains l where "l \<in> s" and "f ----> l"

  4088   using assms unfolding complete_def by fast

  4089

  4090 lemma compact_imp_complete:

  4091   assumes "compact s"

  4092   shows "complete s"

  4093 proof -

  4094   {

  4095     fix f

  4096     assume as: "(\<forall>n::nat. f n \<in> s)" "Cauchy f"

  4097     from as(1) obtain l r where lr: "l\<in>s" "subseq r" "(f \<circ> r) ----> l"

  4098       using assms unfolding compact_def by blast

  4099

  4100     note lr' = seq_suble [OF lr(2)]

  4101     {

  4102       fix e :: real

  4103       assume "e > 0"

  4104       from as(2) obtain N where N:"\<forall>m n. N \<le> m \<and> N \<le> n \<longrightarrow> dist (f m) (f n) < e/2"

  4105         unfolding cauchy_def

  4106         using e > 0

  4107         apply (erule_tac x="e/2" in allE)

  4108         apply auto

  4109         done

  4110       from lr(3)[unfolded LIMSEQ_def, THEN spec[where x="e/2"]]

  4111       obtain M where M:"\<forall>n\<ge>M. dist ((f \<circ> r) n) l < e/2"

  4112         using e > 0 by auto

  4113       {

  4114         fix n :: nat

  4115         assume n: "n \<ge> max N M"

  4116         have "dist ((f \<circ> r) n) l < e/2"

  4117           using n M by auto

  4118         moreover have "r n \<ge> N"

  4119           using lr'[of n] n by auto

  4120         then have "dist (f n) ((f \<circ> r) n) < e / 2"

  4121           using N and n by auto

  4122         ultimately have "dist (f n) l < e"

  4123           using dist_triangle_half_r[of "f (r n)" "f n" e l]

  4124           by (auto simp add: dist_commute)

  4125       }

  4126       then have "\<exists>N. \<forall>n\<ge>N. dist (f n) l < e" by blast

  4127     }

  4128     then have "\<exists>l\<in>s. (f ---> l) sequentially" using l\<in>s

  4129       unfolding LIMSEQ_def by auto

  4130   }

  4131   then show ?thesis unfolding complete_def by auto

  4132 qed

  4133

  4134 lemma nat_approx_posE:

  4135   fixes e::real

  4136   assumes "0 < e"

  4137   obtains n :: nat where "1 / (Suc n) < e"

  4138 proof atomize_elim

  4139   have " 1 / real (Suc (nat (ceiling (1/e)))) < 1 / (ceiling (1/e))"

  4140     by (rule divide_strict_left_mono) (auto simp: 0 < e)

  4141   also have "1 / (ceiling (1/e)) \<le> 1 / (1/e)"

  4142     by (rule divide_left_mono) (auto simp: 0 < e)

  4143   also have "\<dots> = e" by simp

  4144   finally show  "\<exists>n. 1 / real (Suc n) < e" ..

  4145 qed

  4146

  4147 lemma compact_eq_totally_bounded:

  4148   "compact s \<longleftrightarrow> complete s \<and> (\<forall>e>0. \<exists>k. finite k \<and> s \<subseteq> (\<Union>((\<lambda>x. ball x e)  k)))"

  4149     (is "_ \<longleftrightarrow> ?rhs")

  4150 proof

  4151   assume assms: "?rhs"

  4152   then obtain k where k: "\<And>e. 0 < e \<Longrightarrow> finite (k e)" "\<And>e. 0 < e \<Longrightarrow> s \<subseteq> (\<Union>x\<in>k e. ball x e)"

  4153     by (auto simp: choice_iff')

  4154

  4155   show "compact s"

  4156   proof cases

  4157     assume "s = {}"

  4158     then show "compact s" by (simp add: compact_def)

  4159   next

  4160     assume "s \<noteq> {}"

  4161     show ?thesis

  4162       unfolding compact_def

  4163     proof safe

  4164       fix f :: "nat \<Rightarrow> 'a"

  4165       assume f: "\<forall>n. f n \<in> s"

  4166

  4167       def e \<equiv> "\<lambda>n. 1 / (2 * Suc n)"

  4168       then have [simp]: "\<And>n. 0 < e n" by auto

  4169       def B \<equiv> "\<lambda>n U. SOME b. infinite {n. f n \<in> b} \<and> (\<exists>x. b \<subseteq> ball x (e n) \<inter> U)"

  4170       {

  4171         fix n U

  4172         assume "infinite {n. f n \<in> U}"

  4173         then have "\<exists>b\<in>k (e n). infinite {i\<in>{n. f n \<in> U}. f i \<in> ball b (e n)}"

  4174           using k f by (intro pigeonhole_infinite_rel) (auto simp: subset_eq)

  4175         then obtain a where

  4176           "a \<in> k (e n)"

  4177           "infinite {i \<in> {n. f n \<in> U}. f i \<in> ball a (e n)}" ..

  4178         then have "\<exists>b. infinite {i. f i \<in> b} \<and> (\<exists>x. b \<subseteq> ball x (e n) \<inter> U)"

  4179           by (intro exI[of _ "ball a (e n) \<inter> U"] exI[of _ a]) (auto simp: ac_simps)

  4180         from someI_ex[OF this]

  4181         have "infinite {i. f i \<in> B n U}" "\<exists>x. B n U \<subseteq> ball x (e n) \<inter> U"

  4182           unfolding B_def by auto

  4183       }

  4184       note B = this

  4185

  4186       def F \<equiv> "rec_nat (B 0 UNIV) B"

  4187       {

  4188         fix n

  4189         have "infinite {i. f i \<in> F n}"

  4190           by (induct n) (auto simp: F_def B)

  4191       }

  4192       then have F: "\<And>n. \<exists>x. F (Suc n) \<subseteq> ball x (e n) \<inter> F n"

  4193         using B by (simp add: F_def)

  4194       then have F_dec: "\<And>m n. m \<le> n \<Longrightarrow> F n \<subseteq> F m"

  4195         using decseq_SucI[of F] by (auto simp: decseq_def)

  4196

  4197       obtain sel where sel: "\<And>k i. i < sel k i" "\<And>k i. f (sel k i) \<in> F k"

  4198       proof (atomize_elim, unfold all_conj_distrib[symmetric], intro choice allI)

  4199         fix k i

  4200         have "infinite ({n. f n \<in> F k} - {.. i})"

  4201           using infinite {n. f n \<in> F k} by auto

  4202         from infinite_imp_nonempty[OF this]

  4203         show "\<exists>x>i. f x \<in> F k"

  4204           by (simp add: set_eq_iff not_le conj_commute)

  4205       qed

  4206

  4207       def t \<equiv> "rec_nat (sel 0 0) (\<lambda>n i. sel (Suc n) i)"

  4208       have "subseq t"

  4209         unfolding subseq_Suc_iff by (simp add: t_def sel)

  4210       moreover have "\<forall>i. (f \<circ> t) i \<in> s"

  4211         using f by auto

  4212       moreover

  4213       {

  4214         fix n

  4215         have "(f \<circ> t) n \<in> F n"

  4216           by (cases n) (simp_all add: t_def sel)

  4217       }

  4218       note t = this

  4219

  4220       have "Cauchy (f \<circ> t)"

  4221       proof (safe intro!: metric_CauchyI exI elim!: nat_approx_posE)

  4222         fix r :: real and N n m

  4223         assume "1 / Suc N < r" "Suc N \<le> n" "Suc N \<le> m"

  4224         then have "(f \<circ> t) n \<in> F (Suc N)" "(f \<circ> t) m \<in> F (Suc N)" "2 * e N < r"

  4225           using F_dec t by (auto simp: e_def field_simps real_of_nat_Suc)

  4226         with F[of N] obtain x where "dist x ((f \<circ> t) n) < e N" "dist x ((f \<circ> t) m) < e N"

  4227           by (auto simp: subset_eq)

  4228         with dist_triangle[of "(f \<circ> t) m" "(f \<circ> t) n" x] 2 * e N < r

  4229         show "dist ((f \<circ> t) m) ((f \<circ> t) n) < r"

  4230           by (simp add: dist_commute)

  4231       qed

  4232

  4233       ultimately show "\<exists>l\<in>s. \<exists>r. subseq r \<and> (f \<circ> r) ----> l"

  4234         using assms unfolding complete_def by blast

  4235     qed

  4236   qed

  4237 qed (metis compact_imp_complete compact_imp_seq_compact seq_compact_imp_totally_bounded)

  4238

  4239 lemma cauchy: "Cauchy s \<longleftrightarrow> (\<forall>e>0.\<exists> N::nat. \<forall>n\<ge>N. dist(s n)(s N) < e)" (is "?lhs = ?rhs")

  4240 proof -

  4241   {

  4242     assume ?rhs

  4243     {

  4244       fix e::real

  4245       assume "e>0"

  4246       with ?rhs obtain N where N:"\<forall>n\<ge>N. dist (s n) (s N) < e/2"

  4247         by (erule_tac x="e/2" in allE) auto

  4248       {

  4249         fix n m

  4250         assume nm:"N \<le> m \<and> N \<le> n"

  4251         then have "dist (s m) (s n) < e" using N

  4252           using dist_triangle_half_l[of "s m" "s N" "e" "s n"]

  4253           by blast

  4254       }

  4255       then have "\<exists>N. \<forall>m n. N \<le> m \<and> N \<le> n \<longrightarrow> dist (s m) (s n) < e"

  4256         by blast

  4257     }

  4258     then have ?lhs

  4259       unfolding cauchy_def

  4260       by blast

  4261   }

  4262   then show ?thesis

  4263     unfolding cauchy_def

  4264     using dist_triangle_half_l

  4265     by blast

  4266 qed

  4267

  4268 lemma cauchy_imp_bounded:

  4269   assumes "Cauchy s"

  4270   shows "bounded (range s)"

  4271 proof -

  4272   from assms obtain N :: nat where "\<forall>m n. N \<le> m \<and> N \<le> n \<longrightarrow> dist (s m) (s n) < 1"

  4273     unfolding cauchy_def

  4274     apply (erule_tac x= 1 in allE)

  4275     apply auto

  4276     done

  4277   then have N:"\<forall>n. N \<le> n \<longrightarrow> dist (s N) (s n) < 1" by auto

  4278   moreover

  4279   have "bounded (s  {0..N})"

  4280     using finite_imp_bounded[of "s  {1..N}"] by auto

  4281   then obtain a where a:"\<forall>x\<in>s  {0..N}. dist (s N) x \<le> a"

  4282     unfolding bounded_any_center [where a="s N"] by auto

  4283   ultimately show "?thesis"

  4284     unfolding bounded_any_center [where a="s N"]

  4285     apply (rule_tac x="max a 1" in exI)

  4286     apply auto

  4287     apply (erule_tac x=y in allE)

  4288     apply (erule_tac x=y in ballE)

  4289     apply auto

  4290     done

  4291 qed

  4292

  4293 instance heine_borel < complete_space

  4294 proof

  4295   fix f :: "nat \<Rightarrow> 'a" assume "Cauchy f"

  4296   then have "bounded (range f)"

  4297     by (rule cauchy_imp_bounded)

  4298   then have "compact (closure (range f))"

  4299     unfolding compact_eq_bounded_closed by auto

  4300   then have "complete (closure (range f))"

  4301     by (rule compact_imp_complete)

  4302   moreover have "\<forall>n. f n \<in> closure (range f)"

  4303     using closure_subset [of "range f"] by auto

  4304   ultimately have "\<exists>l\<in>closure (range f). (f ---> l) sequentially"

  4305     using Cauchy f unfolding complete_def by auto

  4306   then show "convergent f"

  4307     unfolding convergent_def by auto

  4308 qed

  4309

  4310 instance euclidean_space \<subseteq> banach ..

  4311

  4312 lemma complete_UNIV: "complete (UNIV :: ('a::complete_space) set)"

  4313 proof (rule completeI)

  4314   fix f :: "nat \<Rightarrow> 'a" assume "Cauchy f"

  4315   then have "convergent f" by (rule Cauchy_convergent)

  4316   then show "\<exists>l\<in>UNIV. f ----> l" unfolding convergent_def by simp

  4317 qed

  4318

  4319 lemma complete_imp_closed:

  4320   assumes "complete s"

  4321   shows "closed s"

  4322 proof (unfold closed_sequential_limits, clarify)

  4323   fix f x assume "\<forall>n. f n \<in> s" and "f ----> x"

  4324   from f ----> x have "Cauchy f"

  4325     by (rule LIMSEQ_imp_Cauchy)

  4326   with complete s and \<forall>n. f n \<in> s obtain l where "l \<in> s" and "f ----> l"

  4327     by (rule completeE)

  4328   from f ----> x and f ----> l have "x = l"

  4329     by (rule LIMSEQ_unique)

  4330   with l \<in> s show "x \<in> s"

  4331     by simp

  4332 qed

  4333

  4334 lemma complete_inter_closed:

  4335   assumes "complete s" and "closed t"

  4336   shows "complete (s \<inter> t)"

  4337 proof (rule completeI)

  4338   fix f assume "\<forall>n. f n \<in> s \<inter> t" and "Cauchy f"

  4339   then have "\<forall>n. f n \<in> s" and "\<forall>n. f n \<in> t"

  4340     by simp_all

  4341   from complete s obtain l where "l \<in> s" and "f ----> l"

  4342     using \<forall>n. f n \<in> s and Cauchy f by (rule completeE)

  4343   from closed t and \<forall>n. f n \<in> t and f ----> l have "l \<in> t"

  4344     by (rule closed_sequentially)

  4345   with l \<in> s and f ----> l show "\<exists>l\<in>s \<inter> t. f ----> l"

  4346     by fast

  4347 qed

  4348

  4349 lemma complete_closed_subset:

  4350   assumes "closed s" and "s \<subseteq> t" and "complete t"

  4351   shows "complete s"

  4352   using assms complete_inter_closed [of t s] by (simp add: Int_absorb1)

  4353

  4354 lemma complete_eq_closed:

  4355   fixes s :: "('a::complete_space) set"

  4356   shows "complete s \<longleftrightarrow> closed s"

  4357 proof

  4358   assume "closed s" then show "complete s"

  4359     using subset_UNIV complete_UNIV by (rule complete_closed_subset)

  4360 next

  4361   assume "complete s" then show "closed s"

  4362     by (rule complete_imp_closed)

  4363 qed

  4364

  4365 lemma convergent_eq_cauchy:

  4366   fixes s :: "nat \<Rightarrow> 'a::complete_space"

  4367   shows "(\<exists>l. (s ---> l) sequentially) \<longleftrightarrow> Cauchy s"

  4368   unfolding Cauchy_convergent_iff convergent_def ..

  4369

  4370 lemma convergent_imp_bounded:

  4371   fixes s :: "nat \<Rightarrow> 'a::metric_space"

  4372   shows "(s ---> l) sequentially \<Longrightarrow> bounded (range s)"

  4373   by (intro cauchy_imp_bounded LIMSEQ_imp_Cauchy)

  4374

  4375 lemma compact_cball[simp]:

  4376   fixes x :: "'a::heine_borel"

  4377   shows "compact (cball x e)"

  4378   using compact_eq_bounded_closed bounded_cball closed_cball

  4379   by blast

  4380

  4381 lemma compact_frontier_bounded[intro]:

  4382   fixes s :: "'a::heine_borel set"

  4383   shows "bounded s \<Longrightarrow> compact (frontier s)"

  4384   unfolding frontier_def

  4385   using compact_eq_bounded_closed

  4386   by blast

  4387

  4388 lemma compact_frontier[intro]:

  4389   fixes s :: "'a::heine_borel set"

  4390   shows "compact s \<Longrightarrow> compact (frontier s)"

  4391   using compact_eq_bounded_closed compact_frontier_bounded

  4392   by blast

  4393

  4394 lemma frontier_subset_compact:

  4395   fixes s :: "'a::heine_borel set"

  4396   shows "compact s \<Longrightarrow> frontier s \<subseteq> s"

  4397   using frontier_subset_closed compact_eq_bounded_closed

  4398   by blast

  4399

  4400 subsection {* Bounded closed nest property (proof does not use Heine-Borel) *}

  4401

  4402 lemma bounded_closed_nest:

  4403   fixes s :: "nat \<Rightarrow> ('a::heine_borel) set"

  4404   assumes "\<forall>n. closed (s n)"

  4405     and "\<forall>n. s n \<noteq> {}"

  4406     and "\<forall>m n. m \<le> n \<longrightarrow> s n \<subseteq> s m"

  4407     and "bounded (s 0)"

  4408   shows "\<exists>a. \<forall>n. a \<in> s n"

  4409 proof -

  4410   from assms(2) obtain x where x: "\<forall>n. x n \<in> s n"

  4411     using choice[of "\<lambda>n x. x \<in> s n"] by auto

  4412   from assms(4,1) have "seq_compact (s 0)"

  4413     by (simp add: bounded_closed_imp_seq_compact)

  4414   then obtain l r where lr: "l \<in> s 0" "subseq r" "(x \<circ> r) ----> l"

  4415     using x and assms(3) unfolding seq_compact_def by blast

  4416   have "\<forall>n. l \<in> s n"

  4417   proof

  4418     fix n :: nat

  4419     have "closed (s n)"

  4420       using assms(1) by simp

  4421     moreover have "\<forall>i. (x \<circ> r) i \<in> s i"

  4422       using x and assms(3) and lr(2) [THEN seq_suble] by auto

  4423     then have "\<forall>i. (x \<circ> r) (i + n) \<in> s n"

  4424       using assms(3) by (fast intro!: le_add2)

  4425     moreover have "(\<lambda>i. (x \<circ> r) (i + n)) ----> l"

  4426       using lr(3) by (rule LIMSEQ_ignore_initial_segment)

  4427     ultimately show "l \<in> s n"

  4428       by (rule closed_sequentially)

  4429   qed

  4430   then show ?thesis ..

  4431 qed

  4432

  4433 text {* Decreasing case does not even need compactness, just completeness. *}

  4434

  4435 lemma decreasing_closed_nest:

  4436   fixes s :: "nat \<Rightarrow> ('a::complete_space) set"

  4437   assumes

  4438     "\<forall>n. closed (s n)"

  4439     "\<forall>n. s n \<noteq> {}"

  4440     "\<forall>m n. m \<le> n \<longrightarrow> s n \<subseteq> s m"

  4441     "\<forall>e>0. \<exists>n. \<forall>x\<in>s n. \<forall>y\<in>s n. dist x y < e"

  4442   shows "\<exists>a. \<forall>n. a \<in> s n"

  4443 proof -

  4444   have "\<forall>n. \<exists>x. x \<in> s n"

  4445     using assms(2) by auto

  4446   then have "\<exists>t. \<forall>n. t n \<in> s n"

  4447     using choice[of "\<lambda>n x. x \<in> s n"] by auto

  4448   then obtain t where t: "\<forall>n. t n \<in> s n" by auto

  4449   {

  4450     fix e :: real

  4451     assume "e > 0"

  4452     then obtain N where N:"\<forall>x\<in>s N. \<forall>y\<in>s N. dist x y < e"

  4453       using assms(4) by auto

  4454     {

  4455       fix m n :: nat

  4456       assume "N \<le> m \<and> N \<le> n"

  4457       then have "t m \<in> s N" "t n \<in> s N"

  4458         using assms(3) t unfolding  subset_eq t by blast+

  4459       then have "dist (t m) (t n) < e"

  4460         using N by auto

  4461     }

  4462     then have "\<exists>N. \<forall>m n. N \<le> m \<and> N \<le> n \<longrightarrow> dist (t m) (t n) < e"

  4463       by auto

  4464   }

  4465   then have "Cauchy t"

  4466     unfolding cauchy_def by auto

  4467   then obtain l where l:"(t ---> l) sequentially"

  4468     using complete_UNIV unfolding complete_def by auto

  4469   {

  4470     fix n :: nat

  4471     {

  4472       fix e :: real

  4473       assume "e > 0"

  4474       then obtain N :: nat where N: "\<forall>n\<ge>N. dist (t n) l < e"

  4475         using l[unfolded LIMSEQ_def] by auto

  4476       have "t (max n N) \<in> s n"

  4477         using assms(3)

  4478         unfolding subset_eq

  4479         apply (erule_tac x=n in allE)

  4480         apply (erule_tac x="max n N" in allE)

  4481         using t

  4482         apply auto

  4483         done

  4484       then have "\<exists>y\<in>s n. dist y l < e"

  4485         apply (rule_tac x="t (max n N)" in bexI)

  4486         using N

  4487         apply auto

  4488         done

  4489     }

  4490     then have "l \<in> s n"

  4491       using closed_approachable[of "s n" l] assms(1) by auto

  4492   }

  4493   then show ?thesis by auto

  4494 qed

  4495

  4496 text {* Strengthen it to the intersection actually being a singleton. *}

  4497

  4498 lemma decreasing_closed_nest_sing:

  4499   fixes s :: "nat \<Rightarrow> 'a::complete_space set"

  4500   assumes

  4501     "\<forall>n. closed(s n)"

  4502     "\<forall>n. s n \<noteq> {}"

  4503     "\<forall>m n. m \<le> n \<longrightarrow> s n \<subseteq> s m"

  4504     "\<forall>e>0. \<exists>n. \<forall>x \<in> (s n). \<forall> y\<in>(s n). dist x y < e"

  4505   shows "\<exists>a. \<Inter>(range s) = {a}"

  4506 proof -

  4507   obtain a where a: "\<forall>n. a \<in> s n"

  4508     using decreasing_closed_nest[of s] using assms by auto

  4509   {

  4510     fix b

  4511     assume b: "b \<in> \<Inter>(range s)"

  4512     {

  4513       fix e :: real

  4514       assume "e > 0"

  4515       then have "dist a b < e"

  4516         using assms(4) and b and a by blast

  4517     }

  4518     then have "dist a b = 0"

  4519       by (metis dist_eq_0_iff dist_nz less_le)

  4520   }

  4521   with a have "\<Inter>(range s) = {a}"

  4522     unfolding image_def by auto

  4523   then show ?thesis ..

  4524 qed

  4525

  4526 text{* Cauchy-type criteria for uniform convergence. *}

  4527

  4528 lemma uniformly_convergent_eq_cauchy:

  4529   fixes s::"nat \<Rightarrow> 'b \<Rightarrow> 'a::complete_space"

  4530   shows

  4531     "(\<exists>l. \<forall>e>0. \<exists>N. \<forall>n x. N \<le> n \<and> P x \<longrightarrow> dist(s n x)(l x) < e) \<longleftrightarrow>

  4532       (\<forall>e>0. \<exists>N. \<forall>m n x. N \<le> m \<and> N \<le> n \<and> P x  \<longrightarrow> dist (s m x) (s n x) < e)"

  4533   (is "?lhs = ?rhs")

  4534 proof

  4535   assume ?lhs

  4536   then obtain l where l:"\<forall>e>0. \<exists>N. \<forall>n x. N \<le> n \<and> P x \<longrightarrow> dist (s n x) (l x) < e"

  4537     by auto

  4538   {

  4539     fix e :: real

  4540     assume "e > 0"

  4541     then obtain N :: nat where N: "\<forall>n x. N \<le> n \<and> P x \<longrightarrow> dist (s n x) (l x) < e / 2"

  4542       using l[THEN spec[where x="e/2"]] by auto

  4543     {

  4544       fix n m :: nat and x :: "'b"

  4545       assume "N \<le> m \<and> N \<le> n \<and> P x"

  4546       then have "dist (s m x) (s n x) < e"

  4547         using N[THEN spec[where x=m], THEN spec[where x=x]]

  4548         using N[THEN spec[where x=n], THEN spec[where x=x]]

  4549         using dist_triangle_half_l[of "s m x" "l x" e "s n x"] by auto

  4550     }

  4551     then have "\<exists>N. \<forall>m n x. N \<le> m \<and> N \<le> n \<and> P x  --> dist (s m x) (s n x) < e"  by auto

  4552   }

  4553   then show ?rhs by auto

  4554 next

  4555   assume ?rhs

  4556   then have "\<forall>x. P x \<longrightarrow> Cauchy (\<lambda>n. s n x)"

  4557     unfolding cauchy_def

  4558     apply auto

  4559     apply (erule_tac x=e in allE)

  4560     apply auto

  4561     done

  4562   then obtain l where l: "\<forall>x. P x \<longrightarrow> ((\<lambda>n. s n x) ---> l x) sequentially"

  4563     unfolding convergent_eq_cauchy[symmetric]

  4564     using choice[of "\<lambda>x l. P x \<longrightarrow> ((\<lambda>n. s n x) ---> l) sequentially"]

  4565     by auto

  4566   {

  4567     fix e :: real

  4568     assume "e > 0"

  4569     then obtain N where N:"\<forall>m n x. N \<le> m \<and> N \<le> n \<and> P x \<longrightarrow> dist (s m x) (s n x) < e/2"

  4570       using ?rhs[THEN spec[where x="e/2"]] by auto

  4571     {

  4572       fix x

  4573       assume "P x"

  4574       then obtain M where M:"\<forall>n\<ge>M. dist (s n x) (l x) < e/2"

  4575         using l[THEN spec[where x=x], unfolded LIMSEQ_def] and e > 0

  4576         by (auto elim!: allE[where x="e/2"])

  4577       fix n :: nat

  4578       assume "n \<ge> N"

  4579       then have "dist(s n x)(l x) < e"

  4580         using P xand N[THEN spec[where x=n], THEN spec[where x="N+M"], THEN spec[where x=x]]

  4581         using M[THEN spec[where x="N+M"]] and dist_triangle_half_l[of "s n x" "s (N+M) x" e "l x"]

  4582         by (auto simp add: dist_commute)

  4583     }

  4584     then have "\<exists>N. \<forall>n x. N \<le> n \<and> P x \<longrightarrow> dist(s n x)(l x) < e"

  4585       by auto

  4586   }

  4587   then show ?lhs by auto

  4588 qed

  4589

  4590 lemma uniformly_cauchy_imp_uniformly_convergent:

  4591   fixes s :: "nat \<Rightarrow> 'a \<Rightarrow> 'b::complete_space"

  4592   assumes "\<forall>e>0.\<exists>N. \<forall>m (n::nat) x. N \<le> m \<and> N \<le> n \<and> P x --> dist(s m x)(s n x) < e"

  4593     and "\<forall>x. P x --> (\<forall>e>0. \<exists>N. \<forall>n. N \<le> n \<longrightarrow> dist(s n x)(l x) < e)"

  4594   shows "\<forall>e>0. \<exists>N. \<forall>n x. N \<le> n \<and> P x \<longrightarrow> dist(s n x)(l x) < e"

  4595 proof -

  4596   obtain l' where l:"\<forall>e>0. \<exists>N. \<forall>n x. N \<le> n \<and> P x \<longrightarrow> dist (s n x) (l' x) < e"

  4597     using assms(1) unfolding uniformly_convergent_eq_cauchy[symmetric] by auto

  4598   moreover

  4599   {

  4600     fix x

  4601     assume "P x"

  4602     then have "l x = l' x"

  4603       using tendsto_unique[OF trivial_limit_sequentially, of "\<lambda>n. s n x" "l x" "l' x"]

  4604       using l and assms(2) unfolding LIMSEQ_def by blast

  4605   }

  4606   ultimately show ?thesis by auto

  4607 qed

  4608

  4609

  4610 subsection {* Continuity *}

  4611

  4612 text{* Derive the epsilon-delta forms, which we often use as "definitions" *}

  4613

  4614 lemma continuous_within_eps_delta:

  4615   "continuous (at x within s) f \<longleftrightarrow> (\<forall>e>0. \<exists>d>0. \<forall>x'\<in> s.  dist x' x < d --> dist (f x') (f x) < e)"

  4616   unfolding continuous_within and Lim_within

  4617   apply auto

  4618   apply (metis dist_nz dist_self)

  4619   apply blast

  4620   done

  4621

  4622 lemma continuous_at_eps_delta:

  4623   "continuous (at x) f \<longleftrightarrow> (\<forall>e > 0. \<exists>d > 0. \<forall>x'. dist x' x < d \<longrightarrow> dist (f x') (f x) < e)"

  4624   using continuous_within_eps_delta [of x UNIV f] by simp

  4625

  4626 text{* Versions in terms of open balls. *}

  4627

  4628 lemma continuous_within_ball:

  4629   "continuous (at x within s) f \<longleftrightarrow>

  4630     (\<forall>e > 0. \<exists>d > 0. f  (ball x d \<inter> s) \<subseteq> ball (f x) e)"

  4631   (is "?lhs = ?rhs")

  4632 proof

  4633   assume ?lhs

  4634   {

  4635     fix e :: real

  4636     assume "e > 0"

  4637     then obtain d where d: "d>0" "\<forall>xa\<in>s. 0 < dist xa x \<and> dist xa x < d \<longrightarrow> dist (f xa) (f x) < e"

  4638       using ?lhs[unfolded continuous_within Lim_within] by auto

  4639     {

  4640       fix y

  4641       assume "y \<in> f  (ball x d \<inter> s)"

  4642       then have "y \<in> ball (f x) e"

  4643         using d(2)

  4644         unfolding dist_nz[symmetric]

  4645         apply (auto simp add: dist_commute)

  4646         apply (erule_tac x=xa in ballE)

  4647         apply auto

  4648         using e > 0

  4649         apply auto

  4650         done

  4651     }

  4652     then have "\<exists>d>0. f  (ball x d \<inter> s) \<subseteq> ball (f x) e"

  4653       using d > 0

  4654       unfolding subset_eq ball_def by (auto simp add: dist_commute)

  4655   }

  4656   then show ?rhs by auto

  4657 next

  4658   assume ?rhs

  4659   then show ?lhs

  4660     unfolding continuous_within Lim_within ball_def subset_eq

  4661     apply (auto simp add: dist_commute)

  4662     apply (erule_tac x=e in allE)

  4663     apply auto

  4664     done

  4665 qed

  4666

  4667 lemma continuous_at_ball:

  4668   "continuous (at x) f \<longleftrightarrow> (\<forall>e>0. \<exists>d>0. f  (ball x d) \<subseteq> ball (f x) e)" (is "?lhs = ?rhs")

  4669 proof

  4670   assume ?lhs

  4671   then show ?rhs

  4672     unfolding continuous_at Lim_at subset_eq Ball_def Bex_def image_iff mem_ball

  4673     apply auto

  4674     apply (erule_tac x=e in allE)

  4675     apply auto

  4676     apply (rule_tac x=d in exI)

  4677     apply auto

  4678     apply (erule_tac x=xa in allE)

  4679     apply (auto simp add: dist_commute dist_nz)

  4680     unfolding dist_nz[symmetric]

  4681     apply auto

  4682     done

  4683 next

  4684   assume ?rhs

  4685   then show ?lhs

  4686     unfolding continuous_at Lim_at subset_eq Ball_def Bex_def image_iff mem_ball

  4687     apply auto

  4688     apply (erule_tac x=e in allE)

  4689     apply auto

  4690     apply (rule_tac x=d in exI)

  4691     apply auto

  4692     apply (erule_tac x="f xa" in allE)

  4693     apply (auto simp add: dist_commute dist_nz)

  4694     done

  4695 qed

  4696

  4697 text{* Define setwise continuity in terms of limits within the set. *}

  4698

  4699 lemma continuous_on_iff:

  4700   "continuous_on s f \<longleftrightarrow>

  4701     (\<forall>x\<in>s. \<forall>e>0. \<exists>d>0. \<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist (f x') (f x) < e)"

  4702   unfolding continuous_on_def Lim_within

  4703   by (metis dist_pos_lt dist_self)

  4704

  4705 definition uniformly_continuous_on :: "'a set \<Rightarrow> ('a::metric_space \<Rightarrow> 'b::metric_space) \<Rightarrow> bool"

  4706   where "uniformly_continuous_on s f \<longleftrightarrow>

  4707     (\<forall>e>0. \<exists>d>0. \<forall>x\<in>s. \<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist (f x') (f x) < e)"

  4708

  4709 text{* Some simple consequential lemmas. *}

  4710

  4711 lemma uniformly_continuous_imp_continuous:

  4712   "uniformly_continuous_on s f \<Longrightarrow> continuous_on s f"

  4713   unfolding uniformly_continuous_on_def continuous_on_iff by blast

  4714

  4715 lemma continuous_at_imp_continuous_within:

  4716   "continuous (at x) f \<Longrightarrow> continuous (at x within s) f"

  4717   unfolding continuous_within continuous_at using Lim_at_within by auto

  4718

  4719 lemma Lim_trivial_limit: "trivial_limit net \<Longrightarrow> (f ---> l) net"

  4720   by simp

  4721

  4722 lemmas continuous_on = continuous_on_def -- "legacy theorem name"

  4723

  4724 lemma continuous_within_subset:

  4725   "continuous (at x within s) f \<Longrightarrow> t \<subseteq> s \<Longrightarrow> continuous (at x within t) f"

  4726   unfolding continuous_within by(metis tendsto_within_subset)

  4727

  4728 lemma continuous_on_interior:

  4729   "continuous_on s f \<Longrightarrow> x \<in> interior s \<Longrightarrow> continuous (at x) f"

  4730   by (metis continuous_on_eq_continuous_at continuous_on_subset interiorE)

  4731

  4732 lemma continuous_on_eq:

  4733   "(\<forall>x \<in> s. f x = g x) \<Longrightarrow> continuous_on s f \<Longrightarrow> continuous_on s g"

  4734   unfolding continuous_on_def tendsto_def eventually_at_topological

  4735   by simp

  4736

  4737 text {* Characterization of various kinds of continuity in terms of sequences. *}

  4738

  4739 lemma continuous_within_sequentially:

  4740   fixes f :: "'a::metric_space \<Rightarrow> 'b::topological_space"

  4741   shows "continuous (at a within s) f \<longleftrightarrow>

  4742     (\<forall>x. (\<forall>n::nat. x n \<in> s) \<and> (x ---> a) sequentially

  4743          \<longrightarrow> ((f \<circ> x) ---> f a) sequentially)"

  4744   (is "?lhs = ?rhs")

  4745 proof

  4746   assume ?lhs

  4747   {

  4748     fix x :: "nat \<Rightarrow> 'a"

  4749     assume x: "\<forall>n. x n \<in> s" "\<forall>e>0. eventually (\<lambda>n. dist (x n) a < e) sequentially"

  4750     fix T :: "'b set"

  4751     assume "open T" and "f a \<in> T"

  4752     with ?lhs obtain d where "d>0" and d:"\<forall>x\<in>s. 0 < dist x a \<and> dist x a < d \<longrightarrow> f x \<in> T"

  4753       unfolding continuous_within tendsto_def eventually_at by (auto simp: dist_nz)

  4754     have "eventually (\<lambda>n. dist (x n) a < d) sequentially"

  4755       using x(2) d>0 by simp

  4756     then have "eventually (\<lambda>n. (f \<circ> x) n \<in> T) sequentially"

  4757     proof eventually_elim

  4758       case (elim n)

  4759       then show ?case

  4760         using d x(1) f a \<in> T unfolding dist_nz[symmetric] by auto

  4761     qed

  4762   }

  4763   then show ?rhs

  4764     unfolding tendsto_iff tendsto_def by simp

  4765 next

  4766   assume ?rhs

  4767   then show ?lhs

  4768     unfolding continuous_within tendsto_def [where l="f a"]

  4769     by (simp add: sequentially_imp_eventually_within)

  4770 qed

  4771

  4772 lemma continuous_at_sequentially:

  4773   fixes f :: "'a::metric_space \<Rightarrow> 'b::topological_space"

  4774   shows "continuous (at a) f \<longleftrightarrow>

  4775     (\<forall>x. (x ---> a) sequentially --> ((f \<circ> x) ---> f a) sequentially)"

  4776   using continuous_within_sequentially[of a UNIV f] by simp

  4777

  4778 lemma continuous_on_sequentially:

  4779   fixes f :: "'a::metric_space \<Rightarrow> 'b::topological_space"

  4780   shows "continuous_on s f \<longleftrightarrow>

  4781     (\<forall>x. \<forall>a \<in> s. (\<forall>n. x(n) \<in> s) \<and> (x ---> a) sequentially

  4782       --> ((f \<circ> x) ---> f a) sequentially)"

  4783   (is "?lhs = ?rhs")

  4784 proof

  4785   assume ?rhs

  4786   then show ?lhs

  4787     using continuous_within_sequentially[of _ s f]

  4788     unfolding continuous_on_eq_continuous_within

  4789     by auto

  4790 next

  4791   assume ?lhs

  4792   then show ?rhs

  4793     unfolding continuous_on_eq_continuous_within

  4794     using continuous_within_sequentially[of _ s f]

  4795     by auto

  4796 qed

  4797

  4798 lemma uniformly_continuous_on_sequentially:

  4799   "uniformly_continuous_on s f \<longleftrightarrow> (\<forall>x y. (\<forall>n. x n \<in> s) \<and> (\<forall>n. y n \<in> s) \<and>

  4800                     ((\<lambda>n. dist (x n) (y n)) ---> 0) sequentially

  4801                     \<longrightarrow> ((\<lambda>n. dist (f(x n)) (f(y n))) ---> 0) sequentially)" (is "?lhs = ?rhs")

  4802 proof

  4803   assume ?lhs

  4804   {

  4805     fix x y

  4806     assume x: "\<forall>n. x n \<in> s"

  4807       and y: "\<forall>n. y n \<in> s"

  4808       and xy: "((\<lambda>n. dist (x n) (y n)) ---> 0) sequentially"

  4809     {

  4810       fix e :: real

  4811       assume "e > 0"

  4812       then obtain d where "d > 0" and d: "\<forall>x\<in>s. \<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist (f x') (f x) < e"

  4813         using ?lhs[unfolded uniformly_continuous_on_def, THEN spec[where x=e]] by auto

  4814       obtain N where N: "\<forall>n\<ge>N. dist (x n) (y n) < d"

  4815         using xy[unfolded LIMSEQ_def dist_norm] and d>0 by auto

  4816       {

  4817         fix n

  4818         assume "n\<ge>N"

  4819         then have "dist (f (x n)) (f (y n)) < e"

  4820           using N[THEN spec[where x=n]]

  4821           using d[THEN bspec[where x="x n"], THEN bspec[where x="y n"]]

  4822           using x and y

  4823           unfolding dist_commute

  4824           by simp

  4825       }

  4826       then have "\<exists>N. \<forall>n\<ge>N. dist (f (x n)) (f (y n)) < e"

  4827         by auto

  4828     }

  4829     then have "((\<lambda>n. dist (f(x n)) (f(y n))) ---> 0) sequentially"

  4830       unfolding LIMSEQ_def and dist_real_def by auto

  4831   }

  4832   then show ?rhs by auto

  4833 next

  4834   assume ?rhs

  4835   {

  4836     assume "\<not> ?lhs"

  4837     then obtain e where "e > 0" "\<forall>d>0. \<exists>x\<in>s. \<exists>x'\<in>s. dist x' x < d \<and> \<not> dist (f x') (f x) < e"

  4838       unfolding uniformly_continuous_on_def by auto

  4839     then obtain fa where fa:

  4840       "\<forall>x. 0 < x \<longrightarrow> fst (fa x) \<in> s \<and> snd (fa x) \<in> s \<and> dist (fst (fa x)) (snd (fa x)) < x \<and> \<not> dist (f (fst (fa x))) (f (snd (fa x))) < e"

  4841       using choice[of "\<lambda>d x. d>0 \<longrightarrow> fst x \<in> s \<and> snd x \<in> s \<and> dist (snd x) (fst x) < d \<and> \<not> dist (f (snd x)) (f (fst x)) < e"]

  4842       unfolding Bex_def

  4843       by (auto simp add: dist_commute)

  4844     def x \<equiv> "\<lambda>n::nat. fst (fa (inverse (real n + 1)))"

  4845     def y \<equiv> "\<lambda>n::nat. snd (fa (inverse (real n + 1)))"

  4846     have xyn: "\<forall>n. x n \<in> s \<and> y n \<in> s"

  4847       and xy0: "\<forall>n. dist (x n) (y n) < inverse (real n + 1)"

  4848       and fxy:"\<forall>n. \<not> dist (f (x n)) (f (y n)) < e"

  4849       unfolding x_def and y_def using fa

  4850       by auto

  4851     {

  4852       fix e :: real

  4853       assume "e > 0"

  4854       then obtain N :: nat where "N \<noteq> 0" and N: "0 < inverse (real N) \<and> inverse (real N) < e"

  4855         unfolding real_arch_inv[of e] by auto

  4856       {

  4857         fix n :: nat

  4858         assume "n \<ge> N"

  4859         then have "inverse (real n + 1) < inverse (real N)"

  4860           using real_of_nat_ge_zero and N\<noteq>0 by auto

  4861         also have "\<dots> < e" using N by auto

  4862         finally have "inverse (real n + 1) < e" by auto

  4863         then have "dist (x n) (y n) < e"

  4864           using xy0[THEN spec[where x=n]] by auto

  4865       }

  4866       then have "\<exists>N. \<forall>n\<ge>N. dist (x n) (y n) < e" by auto

  4867     }

  4868     then have "\<forall>e>0. \<exists>N. \<forall>n\<ge>N. dist (f (x n)) (f (y n)) < e"

  4869       using ?rhs[THEN spec[where x=x], THEN spec[where x=y]] and xyn

  4870       unfolding LIMSEQ_def dist_real_def by auto

  4871     then have False using fxy and e>0 by auto

  4872   }

  4873   then show ?lhs

  4874     unfolding uniformly_continuous_on_def by blast

  4875 qed

  4876

  4877 text{* The usual transformation theorems. *}

  4878

  4879 lemma continuous_transform_within:

  4880   fixes f g :: "'a::metric_space \<Rightarrow> 'b::topological_space"

  4881   assumes "0 < d"

  4882     and "x \<in> s"

  4883     and "\<forall>x' \<in> s. dist x' x < d --> f x' = g x'"

  4884     and "continuous (at x within s) f"

  4885   shows "continuous (at x within s) g"

  4886   unfolding continuous_within

  4887 proof (rule Lim_transform_within)

  4888   show "0 < d" by fact

  4889   show "\<forall>x'\<in>s. 0 < dist x' x \<and> dist x' x < d \<longrightarrow> f x' = g x'"

  4890     using assms(3) by auto

  4891   have "f x = g x"

  4892     using assms(1,2,3) by auto

  4893   then show "(f ---> g x) (at x within s)"

  4894     using assms(4) unfolding continuous_within by simp

  4895 qed

  4896

  4897 lemma continuous_transform_at:

  4898   fixes f g :: "'a::metric_space \<Rightarrow> 'b::topological_space"

  4899   assumes "0 < d"

  4900     and "\<forall>x'. dist x' x < d --> f x' = g x'"

  4901     and "continuous (at x) f"

  4902   shows "continuous (at x) g"

  4903   using continuous_transform_within [of d x UNIV f g] assms by simp

  4904

  4905

  4906 subsubsection {* Structural rules for pointwise continuity *}

  4907

  4908 lemmas continuous_within_id = continuous_ident

  4909

  4910 lemmas continuous_at_id = isCont_ident

  4911

  4912 lemma continuous_infdist[continuous_intros]:

  4913   assumes "continuous F f"

  4914   shows "continuous F (\<lambda>x. infdist (f x) A)"

  4915   using assms unfolding continuous_def by (rule tendsto_infdist)

  4916

  4917 lemma continuous_infnorm[continuous_intros]:

  4918   "continuous F f \<Longrightarrow> continuous F (\<lambda>x. infnorm (f x))"

  4919   unfolding continuous_def by (rule tendsto_infnorm)

  4920

  4921 lemma continuous_inner[continuous_intros]:

  4922   assumes "continuous F f"

  4923     and "continuous F g"

  4924   shows "continuous F (\<lambda>x. inner (f x) (g x))"

  4925   using assms unfolding continuous_def by (rule tendsto_inner)

  4926

  4927 lemmas continuous_at_inverse = isCont_inverse

  4928

  4929 subsubsection {* Structural rules for setwise continuity *}

  4930

  4931 lemma continuous_on_infnorm[continuous_intros]:

  4932   "continuous_on s f \<Longrightarrow> continuous_on s (\<lambda>x. infnorm (f x))"

  4933   unfolding continuous_on by (fast intro: tendsto_infnorm)

  4934

  4935 lemma continuous_on_inner[continuous_intros]:

  4936   fixes g :: "'a::topological_space \<Rightarrow> 'b::real_inner"

  4937   assumes "continuous_on s f"

  4938     and "continuous_on s g"

  4939   shows "continuous_on s (\<lambda>x. inner (f x) (g x))"

  4940   using bounded_bilinear_inner assms

  4941   by (rule bounded_bilinear.continuous_on)

  4942

  4943 subsubsection {* Structural rules for uniform continuity *}

  4944

  4945 lemma uniformly_continuous_on_id[continuous_intros]:

  4946   "uniformly_continuous_on s (\<lambda>x. x)"

  4947   unfolding uniformly_continuous_on_def by auto

  4948

  4949 lemma uniformly_continuous_on_const[continuous_intros]:

  4950   "uniformly_continuous_on s (\<lambda>x. c)"

  4951   unfolding uniformly_continuous_on_def by simp

  4952

  4953 lemma uniformly_continuous_on_dist[continuous_intros]:

  4954   fixes f g :: "'a::metric_space \<Rightarrow> 'b::metric_space"

  4955   assumes "uniformly_continuous_on s f"

  4956     and "uniformly_continuous_on s g"

  4957   shows "uniformly_continuous_on s (\<lambda>x. dist (f x) (g x))"

  4958 proof -

  4959   {

  4960     fix a b c d :: 'b

  4961     have "\<bar>dist a b - dist c d\<bar> \<le> dist a c + dist b d"

  4962       using dist_triangle2 [of a b c] dist_triangle2 [of b c d]

  4963       using dist_triangle3 [of c d a] dist_triangle [of a d b]

  4964       by arith

  4965   } note le = this

  4966   {

  4967     fix x y

  4968     assume f: "(\<lambda>n. dist (f (x n)) (f (y n))) ----> 0"

  4969     assume g: "(\<lambda>n. dist (g (x n)) (g (y n))) ----> 0"

  4970     have "(\<lambda>n. \<bar>dist (f (x n)) (g (x n)) - dist (f (y n)) (g (y n))\<bar>) ----> 0"

  4971       by (rule Lim_transform_bound [OF _ tendsto_add_zero [OF f g]],

  4972         simp add: le)

  4973   }

  4974   then show ?thesis

  4975     using assms unfolding uniformly_continuous_on_sequentially

  4976     unfolding dist_real_def by simp

  4977 qed

  4978

  4979 lemma uniformly_continuous_on_norm[continuous_intros]:

  4980   assumes "uniformly_continuous_on s f"

  4981   shows "uniformly_continuous_on s (\<lambda>x. norm (f x))"

  4982   unfolding norm_conv_dist using assms

  4983   by (intro uniformly_continuous_on_dist uniformly_continuous_on_const)

  4984

  4985 lemma (in bounded_linear) uniformly_continuous_on[continuous_intros]:

  4986   assumes "uniformly_continuous_on s g"

  4987   shows "uniformly_continuous_on s (\<lambda>x. f (g x))"

  4988   using assms unfolding uniformly_continuous_on_sequentially

  4989   unfolding dist_norm tendsto_norm_zero_iff diff[symmetric]

  4990   by (auto intro: tendsto_zero)

  4991

  4992 lemma uniformly_continuous_on_cmul[continuous_intros]:

  4993   fixes f :: "'a::metric_space \<Rightarrow> 'b::real_normed_vector"

  4994   assumes "uniformly_continuous_on s f"

  4995   shows "uniformly_continuous_on s (\<lambda>x. c *\<^sub>R f(x))"

  4996   using bounded_linear_scaleR_right assms

  4997   by (rule bounded_linear.uniformly_continuous_on)

  4998

  4999 lemma dist_minus:

  5000   fixes x y :: "'a::real_normed_vector"

  5001   shows "dist (- x) (- y) = dist x y"

  5002   unfolding dist_norm minus_diff_minus norm_minus_cancel ..

  5003

  5004 lemma uniformly_continuous_on_minus[continuous_intros]:

  5005   fixes f :: "'a::metric_space \<Rightarrow> 'b::real_normed_vector"

  5006   shows "uniformly_continuous_on s f \<Longrightarrow> uniformly_continuous_on s (\<lambda>x. - f x)"

  5007   unfolding uniformly_continuous_on_def dist_minus .

  5008

  5009 lemma uniformly_continuous_on_add[continuous_intros]:

  5010   fixes f g :: "'a::metric_space \<Rightarrow> 'b::real_normed_vector"

  5011   assumes "uniformly_continuous_on s f"

  5012     and "uniformly_continuous_on s g"

  5013   shows "uniformly_continuous_on s (\<lambda>x. f x + g x)"

  5014   using assms

  5015   unfolding uniformly_continuous_on_sequentially

  5016   unfolding dist_norm tendsto_norm_zero_iff add_diff_add

  5017   by (auto intro: tendsto_add_zero)

  5018

  5019 lemma uniformly_continuous_on_diff[continuous_intros]:

  5020   fixes f :: "'a::metric_space \<Rightarrow> 'b::real_normed_vector"

  5021   assumes "uniformly_continuous_on s f"

  5022     and "uniformly_continuous_on s g"

  5023   shows "uniformly_continuous_on s (\<lambda>x. f x - g x)"

  5024   using assms uniformly_continuous_on_add [of s f "- g"]

  5025     by (simp add: fun_Compl_def uniformly_continuous_on_minus)

  5026

  5027 text{* Continuity of all kinds is preserved under composition. *}

  5028

  5029 lemmas continuous_at_compose = isCont_o

  5030

  5031 lemma uniformly_continuous_on_compose[continuous_intros]:

  5032   assumes "uniformly_continuous_on s f"  "uniformly_continuous_on (f  s) g"

  5033   shows "uniformly_continuous_on s (g \<circ> f)"

  5034 proof -

  5035   {

  5036     fix e :: real

  5037     assume "e > 0"

  5038     then obtain d where "d > 0"

  5039       and d: "\<forall>x\<in>f  s. \<forall>x'\<in>f  s. dist x' x < d \<longrightarrow> dist (g x') (g x) < e"

  5040       using assms(2) unfolding uniformly_continuous_on_def by auto

  5041     obtain d' where "d'>0" "\<forall>x\<in>s. \<forall>x'\<in>s. dist x' x < d' \<longrightarrow> dist (f x') (f x) < d"

  5042       using d > 0 using assms(1) unfolding uniformly_continuous_on_def by auto

  5043     then have "\<exists>d>0. \<forall>x\<in>s. \<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist ((g \<circ> f) x') ((g \<circ> f) x) < e"

  5044       using d>0 using d by auto

  5045   }

  5046   then show ?thesis

  5047     using assms unfolding uniformly_continuous_on_def by auto

  5048 qed

  5049

  5050 text{* Continuity in terms of open preimages. *}

  5051

  5052 lemma continuous_at_open:

  5053   "continuous (at x) f \<longleftrightarrow> (\<forall>t. open t \<and> f x \<in> t --> (\<exists>s. open s \<and> x \<in> s \<and> (\<forall>x' \<in> s. (f x') \<in> t)))"

  5054   unfolding continuous_within_topological [of x UNIV f]

  5055   unfolding imp_conjL

  5056   by (intro all_cong imp_cong ex_cong conj_cong refl) auto

  5057

  5058 lemma continuous_imp_tendsto:

  5059   assumes "continuous (at x0) f"

  5060     and "x ----> x0"

  5061   shows "(f \<circ> x) ----> (f x0)"

  5062 proof (rule topological_tendstoI)

  5063   fix S

  5064   assume "open S" "f x0 \<in> S"

  5065   then obtain T where T_def: "open T" "x0 \<in> T" "\<forall>x\<in>T. f x \<in> S"

  5066      using assms continuous_at_open by metis

  5067   then have "eventually (\<lambda>n. x n \<in> T) sequentially"

  5068     using assms T_def by (auto simp: tendsto_def)

  5069   then show "eventually (\<lambda>n. (f \<circ> x) n \<in> S) sequentially"

  5070     using T_def by (auto elim!: eventually_elim1)

  5071 qed

  5072

  5073 lemma continuous_on_open:

  5074   "continuous_on s f \<longleftrightarrow>

  5075     (\<forall>t. openin (subtopology euclidean (f  s)) t \<longrightarrow>

  5076       openin (subtopology euclidean s) {x \<in> s. f x \<in> t})"

  5077   unfolding continuous_on_open_invariant openin_open Int_def vimage_def Int_commute

  5078   by (simp add: imp_ex imageI conj_commute eq_commute cong: conj_cong)

  5079

  5080 text {* Similarly in terms of closed sets. *}

  5081

  5082 lemma continuous_on_closed:

  5083   "continuous_on s f \<longleftrightarrow>

  5084     (\<forall>t. closedin (subtopology euclidean (f  s)) t \<longrightarrow>

  5085       closedin (subtopology euclidean s) {x \<in> s. f x \<in> t})"

  5086   unfolding continuous_on_closed_invariant closedin_closed Int_def vimage_def Int_commute

  5087   by (simp add: imp_ex imageI conj_commute eq_commute cong: conj_cong)

  5088

  5089 text {* Half-global and completely global cases. *}

  5090

  5091 lemma continuous_open_in_preimage:

  5092   assumes "continuous_on s f"  "open t"

  5093   shows "openin (subtopology euclidean s) {x \<in> s. f x \<in> t}"

  5094 proof -

  5095   have *: "\<forall>x. x \<in> s \<and> f x \<in> t \<longleftrightarrow> x \<in> s \<and> f x \<in> (t \<inter> f  s)"

  5096     by auto

  5097   have "openin (subtopology euclidean (f  s)) (t \<inter> f  s)"

  5098     using openin_open_Int[of t "f  s", OF assms(2)] unfolding openin_open by auto

  5099   then show ?thesis

  5100     using assms(1)[unfolded continuous_on_open, THEN spec[where x="t \<inter> f  s"]]

  5101     using * by auto

  5102 qed

  5103

  5104 lemma continuous_closed_in_preimage:

  5105   assumes "continuous_on s f" and "closed t"

  5106   shows "closedin (subtopology euclidean s) {x \<in> s. f x \<in> t}"

  5107 proof -

  5108   have *: "\<forall>x. x \<in> s \<and> f x \<in> t \<longleftrightarrow> x \<in> s \<and> f x \<in> (t \<inter> f  s)"

  5109     by auto

  5110   have "closedin (subtopology euclidean (f  s)) (t \<inter> f  s)"

  5111     using closedin_closed_Int[of t "f  s", OF assms(2)] unfolding Int_commute

  5112     by auto

  5113   then show ?thesis

  5114     using assms(1)[unfolded continuous_on_closed, THEN spec[where x="t \<inter> f  s"]]

  5115     using * by auto

  5116 qed

  5117

  5118 lemma continuous_open_preimage:

  5119   assumes "continuous_on s f"

  5120     and "open s"

  5121     and "open t"

  5122   shows "open {x \<in> s. f x \<in> t}"

  5123 proof-

  5124   obtain T where T: "open T" "{x \<in> s. f x \<in> t} = s \<inter> T"

  5125     using continuous_open_in_preimage[OF assms(1,3)] unfolding openin_open by auto

  5126   then show ?thesis

  5127     using open_Int[of s T, OF assms(2)] by auto

  5128 qed

  5129

  5130 lemma continuous_closed_preimage:

  5131   assumes "continuous_on s f"

  5132     and "closed s"

  5133     and "closed t"

  5134   shows "closed {x \<in> s. f x \<in> t}"

  5135 proof-

  5136   obtain T where "closed T" "{x \<in> s. f x \<in> t} = s \<inter> T"

  5137     using continuous_closed_in_preimage[OF assms(1,3)]

  5138     unfolding closedin_closed by auto

  5139   then show ?thesis using closed_Int[of s T, OF assms(2)] by auto

  5140 qed

  5141

  5142 lemma continuous_open_preimage_univ:

  5143   "\<forall>x. continuous (at x) f \<Longrightarrow> open s \<Longrightarrow> open {x. f x \<in> s}"

  5144   using continuous_open_preimage[of UNIV f s] open_UNIV continuous_at_imp_continuous_on by auto

  5145

  5146 lemma continuous_closed_preimage_univ:

  5147   "(\<forall>x. continuous (at x) f) \<Longrightarrow> closed s \<Longrightarrow> closed {x. f x \<in> s}"

  5148   using continuous_closed_preimage[of UNIV f s] closed_UNIV continuous_at_imp_continuous_on by auto

  5149

  5150 lemma continuous_open_vimage: "\<forall>x. continuous (at x) f \<Longrightarrow> open s \<Longrightarrow> open (f - s)"

  5151   unfolding vimage_def by (rule continuous_open_preimage_univ)

  5152

  5153 lemma continuous_closed_vimage: "\<forall>x. continuous (at x) f \<Longrightarrow> closed s \<Longrightarrow> closed (f - s)"

  5154   unfolding vimage_def by (rule continuous_closed_preimage_univ)

  5155

  5156 lemma interior_image_subset:

  5157   assumes "\<forall>x. continuous (at x) f"

  5158     and "inj f"

  5159   shows "interior (f  s) \<subseteq> f  (interior s)"

  5160 proof

  5161   fix x assume "x \<in> interior (f  s)"

  5162   then obtain T where as: "open T" "x \<in> T" "T \<subseteq> f  s" ..

  5163   then have "x \<in> f  s" by auto

  5164   then obtain y where y: "y \<in> s" "x = f y" by auto

  5165   have "open (vimage f T)"

  5166     using assms(1) open T by (rule continuous_open_vimage)

  5167   moreover have "y \<in> vimage f T"

  5168     using x = f y x \<in> T by simp

  5169   moreover have "vimage f T \<subseteq> s"

  5170     using T \<subseteq> image f s inj f unfolding inj_on_def subset_eq by auto

  5171   ultimately have "y \<in> interior s" ..

  5172   with x = f y show "x \<in> f  interior s" ..

  5173 qed

  5174

  5175 text {* Equality of continuous functions on closure and related results. *}

  5176

  5177 lemma continuous_closed_in_preimage_constant:

  5178   fixes f :: "_ \<Rightarrow> 'b::t1_space"

  5179   shows "continuous_on s f \<Longrightarrow> closedin (subtopology euclidean s) {x \<in> s. f x = a}"

  5180   using continuous_closed_in_preimage[of s f "{a}"] by auto

  5181

  5182 lemma continuous_closed_preimage_constant:

  5183   fixes f :: "_ \<Rightarrow> 'b::t1_space"

  5184   shows "continuous_on s f \<Longrightarrow> closed s \<Longrightarrow> closed {x \<in> s. f x = a}"

  5185   using continuous_closed_preimage[of s f "{a}"] by auto

  5186

  5187 lemma continuous_constant_on_closure:

  5188   fixes f :: "_ \<Rightarrow> 'b::t1_space"

  5189   assumes "continuous_on (closure s) f"

  5190     and "\<forall>x \<in> s. f x = a"

  5191   shows "\<forall>x \<in> (closure s). f x = a"

  5192     using continuous_closed_preimage_constant[of "closure s" f a]

  5193       assms closure_minimal[of s "{x \<in> closure s. f x = a}"] closure_subset

  5194     unfolding subset_eq

  5195     by auto

  5196

  5197 lemma image_closure_subset:

  5198   assumes "continuous_on (closure s) f"

  5199     and "closed t"

  5200     and "(f  s) \<subseteq> t"

  5201   shows "f  (closure s) \<subseteq> t"

  5202 proof -

  5203   have "s \<subseteq> {x \<in> closure s. f x \<in> t}"

  5204     using assms(3) closure_subset by auto

  5205   moreover have "closed {x \<in> closure s. f x \<in> t}"

  5206     using continuous_closed_preimage[OF assms(1)] and assms(2) by auto

  5207   ultimately have "closure s = {x \<in> closure s . f x \<in> t}"

  5208     using closure_minimal[of s "{x \<in> closure s. f x \<in> t}"] by auto

  5209   then show ?thesis by auto

  5210 qed

  5211

  5212 lemma continuous_on_closure_norm_le:

  5213   fixes f :: "'a::metric_space \<Rightarrow> 'b::real_normed_vector"

  5214   assumes "continuous_on (closure s) f"

  5215     and "\<forall>y \<in> s. norm(f y) \<le> b"

  5216     and "x \<in> (closure s)"

  5217   shows "norm (f x) \<le> b"

  5218 proof -

  5219   have *: "f  s \<subseteq> cball 0 b"

  5220     using assms(2)[unfolded mem_cball_0[symmetric]] by auto

  5221   show ?thesis

  5222     using image_closure_subset[OF assms(1) closed_cball[of 0 b] *] assms(3)

  5223     unfolding subset_eq

  5224     apply (erule_tac x="f x" in ballE)

  5225     apply (auto simp add: dist_norm)

  5226     done

  5227 qed

  5228

  5229 text {* Making a continuous function avoid some value in a neighbourhood. *}

  5230

  5231 lemma continuous_within_avoid:

  5232   fixes f :: "'a::metric_space \<Rightarrow> 'b::t1_space"

  5233   assumes "continuous (at x within s) f"

  5234     and "f x \<noteq> a"

  5235   shows "\<exists>e>0. \<forall>y \<in> s. dist x y < e --> f y \<noteq> a"

  5236 proof -

  5237   obtain U where "open U" and "f x \<in> U" and "a \<notin> U"

  5238     using t1_space [OF f x \<noteq> a] by fast

  5239   have "(f ---> f x) (at x within s)"

  5240     using assms(1) by (simp add: continuous_within)

  5241   then have "eventually (\<lambda>y. f y \<in> U) (at x within s)"

  5242     using open U and f x \<in> U

  5243     unfolding tendsto_def by fast

  5244   then have "eventually (\<lambda>y. f y \<noteq> a) (at x within s)"

  5245     using a \<notin> U by (fast elim: eventually_mono [rotated])

  5246   then show ?thesis

  5247     using f x \<noteq> a by (auto simp: dist_commute zero_less_dist_iff eventually_at)

  5248 qed

  5249

  5250 lemma continuous_at_avoid:

  5251   fixes f :: "'a::metric_space \<Rightarrow> 'b::t1_space"

  5252   assumes "continuous (at x) f"

  5253     and "f x \<noteq> a"

  5254   shows "\<exists>e>0. \<forall>y. dist x y < e \<longrightarrow> f y \<noteq> a"

  5255   using assms continuous_within_avoid[of x UNIV f a] by simp

  5256

  5257 lemma continuous_on_avoid:

  5258   fixes f :: "'a::metric_space \<Rightarrow> 'b::t1_space"

  5259   assumes "continuous_on s f"

  5260     and "x \<in> s"

  5261     and "f x \<noteq> a"

  5262   shows "\<exists>e>0. \<forall>y \<in> s. dist x y < e \<longrightarrow> f y \<noteq> a"

  5263   using assms(1)[unfolded continuous_on_eq_continuous_within, THEN bspec[where x=x],

  5264     OF assms(2)] continuous_within_avoid[of x s f a]

  5265   using assms(3)

  5266   by auto

  5267

  5268 lemma continuous_on_open_avoid:

  5269   fixes f :: "'a::metric_space \<Rightarrow> 'b::t1_space"

  5270   assumes "continuous_on s f"

  5271     and "open s"

  5272     and "x \<in> s"

  5273     and "f x \<noteq> a"

  5274   shows "\<exists>e>0. \<forall>y. dist x y < e \<longrightarrow> f y \<noteq> a"

  5275   using assms(1)[unfolded continuous_on_eq_continuous_at[OF assms(2)], THEN bspec[where x=x], OF assms(3)]

  5276   using continuous_at_avoid[of x f a] assms(4)

  5277   by auto

  5278

  5279 text {* Proving a function is constant by proving open-ness of level set. *}

  5280

  5281 lemma continuous_levelset_open_in_cases:

  5282   fixes f :: "_ \<Rightarrow> 'b::t1_space"

  5283   shows "connected s \<Longrightarrow> continuous_on s f \<Longrightarrow>

  5284         openin (subtopology euclidean s) {x \<in> s. f x = a}

  5285         \<Longrightarrow> (\<forall>x \<in> s. f x \<noteq> a) \<or> (\<forall>x \<in> s. f x = a)"

  5286   unfolding connected_clopen

  5287   using continuous_closed_in_preimage_constant by auto

  5288

  5289 lemma continuous_levelset_open_in:

  5290   fixes f :: "_ \<Rightarrow> 'b::t1_space"

  5291   shows "connected s \<Longrightarrow> continuous_on s f \<Longrightarrow>

  5292         openin (subtopology euclidean s) {x \<in> s. f x = a} \<Longrightarrow>

  5293         (\<exists>x \<in> s. f x = a)  \<Longrightarrow> (\<forall>x \<in> s. f x = a)"

  5294   using continuous_levelset_open_in_cases[of s f ]

  5295   by meson

  5296

  5297 lemma continuous_levelset_open:

  5298   fixes f :: "_ \<Rightarrow> 'b::t1_space"

  5299   assumes "connected s"

  5300     and "continuous_on s f"

  5301     and "open {x \<in> s. f x = a}"

  5302     and "\<exists>x \<in> s.  f x = a"

  5303   shows "\<forall>x \<in> s. f x = a"

  5304   using continuous_levelset_open_in[OF assms(1,2), of a, unfolded openin_open]

  5305   using assms (3,4)

  5306   by fast

  5307

  5308 text {* Some arithmetical combinations (more to prove). *}

  5309

  5310 lemma open_scaling[intro]:

  5311   fixes s :: "'a::real_normed_vector set"

  5312   assumes "c \<noteq> 0"

  5313     and "open s"

  5314   shows "open((\<lambda>x. c *\<^sub>R x)  s)"

  5315 proof -

  5316   {

  5317     fix x

  5318     assume "x \<in> s"

  5319     then obtain e where "e>0"

  5320       and e:"\<forall>x'. dist x' x < e \<longrightarrow> x' \<in> s" using assms(2)[unfolded open_dist, THEN bspec[where x=x]]

  5321       by auto

  5322     have "e * abs c > 0"

  5323       using assms(1)[unfolded zero_less_abs_iff[symmetric]] e>0 by auto

  5324     moreover

  5325     {

  5326       fix y

  5327       assume "dist y (c *\<^sub>R x) < e * \<bar>c\<bar>"

  5328       then have "norm ((1 / c) *\<^sub>R y - x) < e"

  5329         unfolding dist_norm

  5330         using norm_scaleR[of c "(1 / c) *\<^sub>R y - x", unfolded scaleR_right_diff_distrib, unfolded scaleR_scaleR] assms(1)

  5331           assms(1)[unfolded zero_less_abs_iff[symmetric]] by (simp del:zero_less_abs_iff)

  5332       then have "y \<in> op *\<^sub>R c  s"

  5333         using rev_image_eqI[of "(1 / c) *\<^sub>R y" s y "op *\<^sub>R c"]

  5334         using e[THEN spec[where x="(1 / c) *\<^sub>R y"]]

  5335         using assms(1)

  5336         unfolding dist_norm scaleR_scaleR

  5337         by auto

  5338     }

  5339     ultimately have "\<exists>e>0. \<forall>x'. dist x' (c *\<^sub>R x) < e \<longrightarrow> x' \<in> op *\<^sub>R c  s"

  5340       apply (rule_tac x="e * abs c" in exI)

  5341       apply auto

  5342       done

  5343   }

  5344   then show ?thesis unfolding open_dist by auto

  5345 qed

  5346

  5347 lemma minus_image_eq_vimage:

  5348   fixes A :: "'a::ab_group_add set"

  5349   shows "(\<lambda>x. - x)  A = (\<lambda>x. - x) - A"

  5350   by (auto intro!: image_eqI [where f="\<lambda>x. - x"])

  5351

  5352 lemma open_negations:

  5353   fixes s :: "'a::real_normed_vector set"

  5354   shows "open s \<Longrightarrow> open ((\<lambda>x. - x)  s)"

  5355   using open_scaling [of "- 1" s] by simp

  5356

  5357 lemma open_translation:

  5358   fixes s :: "'a::real_normed_vector set"

  5359   assumes "open s"

  5360   shows "open((\<lambda>x. a + x)  s)"

  5361 proof -

  5362   {

  5363     fix x

  5364     have "continuous (at x) (\<lambda>x. x - a)"

  5365       by (intro continuous_diff continuous_at_id continuous_const)

  5366   }

  5367   moreover have "{x. x - a \<in> s} = op + a  s"

  5368     by force

  5369   ultimately show ?thesis using continuous_open_preimage_univ[of "\<lambda>x. x - a" s]

  5370     using assms by auto

  5371 qed

  5372

  5373 lemma open_affinity:

  5374   fixes s :: "'a::real_normed_vector set"

  5375   assumes "open s"  "c \<noteq> 0"

  5376   shows "open ((\<lambda>x. a + c *\<^sub>R x)  s)"

  5377 proof -

  5378   have *: "(\<lambda>x. a + c *\<^sub>R x) = (\<lambda>x. a + x) \<circ> (\<lambda>x. c *\<^sub>R x)"

  5379     unfolding o_def ..

  5380   have "op + a  op *\<^sub>R c  s = (op + a \<circ> op *\<^sub>R c)  s"

  5381     by auto

  5382   then show ?thesis

  5383     using assms open_translation[of "op *\<^sub>R c  s" a]

  5384     unfolding *

  5385     by auto

  5386 qed

  5387

  5388 lemma interior_translation:

  5389   fixes s :: "'a::real_normed_vector set"

  5390   shows "interior ((\<lambda>x. a + x)  s) = (\<lambda>x. a + x)  (interior s)"

  5391 proof (rule set_eqI, rule)

  5392   fix x

  5393   assume "x \<in> interior (op + a  s)"

  5394   then obtain e where "e > 0" and e: "ball x e \<subseteq> op + a  s"

  5395     unfolding mem_interior by auto

  5396   then have "ball (x - a) e \<subseteq> s"

  5397     unfolding subset_eq Ball_def mem_ball dist_norm

  5398     apply auto

  5399     apply (erule_tac x="a + xa" in allE)

  5400     unfolding ab_group_add_class.diff_diff_eq[symmetric]

  5401     apply auto

  5402     done

  5403   then show "x \<in> op + a  interior s"

  5404     unfolding image_iff

  5405     apply (rule_tac x="x - a" in bexI)

  5406     unfolding mem_interior

  5407     using e > 0

  5408     apply auto

  5409     done

  5410 next

  5411   fix x

  5412   assume "x \<in> op + a  interior s"

  5413   then obtain y e where "e > 0" and e: "ball y e \<subseteq> s" and y: "x = a + y"

  5414     unfolding image_iff Bex_def mem_interior by auto

  5415   {

  5416     fix z

  5417     have *: "a + y - z = y + a - z" by auto

  5418     assume "z \<in> ball x e"

  5419     then have "z - a \<in> s"

  5420       using e[unfolded subset_eq, THEN bspec[where x="z - a"]]

  5421       unfolding mem_ball dist_norm y group_add_class.diff_diff_eq2 *

  5422       by auto

  5423     then have "z \<in> op + a  s"

  5424       unfolding image_iff by (auto intro!: bexI[where x="z - a"])

  5425   }

  5426   then have "ball x e \<subseteq> op + a  s"

  5427     unfolding subset_eq by auto

  5428   then show "x \<in> interior (op + a  s)"

  5429     unfolding mem_interior using e > 0 by auto

  5430 qed

  5431

  5432 text {* Topological properties of linear functions. *}

  5433

  5434 lemma linear_lim_0:

  5435   assumes "bounded_linear f"

  5436   shows "(f ---> 0) (at (0))"

  5437 proof -

  5438   interpret f: bounded_linear f by fact

  5439   have "(f ---> f 0) (at 0)"

  5440     using tendsto_ident_at by (rule f.tendsto)

  5441   then show ?thesis unfolding f.zero .

  5442 qed

  5443

  5444 lemma linear_continuous_at:

  5445   assumes "bounded_linear f"

  5446   shows "continuous (at a) f"

  5447   unfolding continuous_at using assms

  5448   apply (rule bounded_linear.tendsto)

  5449   apply (rule tendsto_ident_at)

  5450   done

  5451

  5452 lemma linear_continuous_within:

  5453   "bounded_linear f \<Longrightarrow> continuous (at x within s) f"

  5454   using continuous_at_imp_continuous_within[of x f s] using linear_continuous_at[of f] by auto

  5455

  5456 lemma linear_continuous_on:

  5457   "bounded_linear f \<Longrightarrow> continuous_on s f"

  5458   using continuous_at_imp_continuous_on[of s f] using linear_continuous_at[of f] by auto

  5459

  5460 text {* Also bilinear functions, in composition form. *}

  5461

  5462 lemma bilinear_continuous_at_compose:

  5463   "continuous (at x) f \<Longrightarrow> continuous (at x) g \<Longrightarrow> bounded_bilinear h \<Longrightarrow>

  5464     continuous (at x) (\<lambda>x. h (f x) (g x))"

  5465   unfolding continuous_at

  5466   using Lim_bilinear[of f "f x" "(at x)" g "g x" h]

  5467   by auto

  5468

  5469 lemma bilinear_continuous_within_compose:

  5470   "continuous (at x within s) f \<Longrightarrow> continuous (at x within s) g \<Longrightarrow> bounded_bilinear h \<Longrightarrow>

  5471     continuous (at x within s) (\<lambda>x. h (f x) (g x))"

  5472   unfolding continuous_within

  5473   using Lim_bilinear[of f "f x"]

  5474   by auto

  5475

  5476 lemma bilinear_continuous_on_compose:

  5477   "continuous_on s f \<Longrightarrow> continuous_on s g \<Longrightarrow> bounded_bilinear h \<Longrightarrow>

  5478     continuous_on s (\<lambda>x. h (f x) (g x))"

  5479   unfolding continuous_on_def

  5480   by (fast elim: bounded_bilinear.tendsto)

  5481

  5482 text {* Preservation of compactness and connectedness under continuous function. *}

  5483

  5484 lemma compact_eq_openin_cover:

  5485   "compact S \<longleftrightarrow>

  5486     (\<forall>C. (\<forall>c\<in>C. openin (subtopology euclidean S) c) \<and> S \<subseteq> \<Union>C \<longrightarrow>

  5487       (\<exists>D\<subseteq>C. finite D \<and> S \<subseteq> \<Union>D))"

  5488 proof safe

  5489   fix C

  5490   assume "compact S" and "\<forall>c\<in>C. openin (subtopology euclidean S) c" and "S \<subseteq> \<Union>C"

  5491   then have "\<forall>c\<in>{T. open T \<and> S \<inter> T \<in> C}. open c" and "S \<subseteq> \<Union>{T. open T \<and> S \<inter> T \<in> C}"

  5492     unfolding openin_open by force+

  5493   with compact S obtain D where "D \<subseteq> {T. open T \<and> S \<inter> T \<in> C}" and "finite D" and "S \<subseteq> \<Union>D"

  5494     by (rule compactE)

  5495   then have "image (\<lambda>T. S \<inter> T) D \<subseteq> C \<and> finite (image (\<lambda>T. S \<inter> T) D) \<and> S \<subseteq> \<Union>(image (\<lambda>T. S \<inter> T) D)"

  5496     by auto

  5497   then show "\<exists>D\<subseteq>C. finite D \<and> S \<subseteq> \<Union>D" ..

  5498 next

  5499   assume 1: "\<forall>C. (\<forall>c\<in>C. openin (subtopology euclidean S) c) \<and> S \<subseteq> \<Union>C \<longrightarrow>

  5500         (\<exists>D\<subseteq>C. finite D \<and> S \<subseteq> \<Union>D)"

  5501   show "compact S"

  5502   proof (rule compactI)

  5503     fix C

  5504     let ?C = "image (\<lambda>T. S \<inter> T) C"

  5505     assume "\<forall>t\<in>C. open t" and "S \<subseteq> \<Union>C"

  5506     then have "(\<forall>c\<in>?C. openin (subtopology euclidean S) c) \<and> S \<subseteq> \<Union>?C"

  5507       unfolding openin_open by auto

  5508     with 1 obtain D where "D \<subseteq> ?C" and "finite D" and "S \<subseteq> \<Union>D"

  5509       by metis

  5510     let ?D = "inv_into C (\<lambda>T. S \<inter> T)  D"

  5511     have "?D \<subseteq> C \<and> finite ?D \<and> S \<subseteq> \<Union>?D"

  5512     proof (intro conjI)

  5513       from D \<subseteq> ?C show "?D \<subseteq> C"

  5514         by (fast intro: inv_into_into)

  5515       from finite D show "finite ?D"

  5516         by (rule finite_imageI)

  5517       from S \<subseteq> \<Union>D show "S \<subseteq> \<Union>?D"

  5518         apply (rule subset_trans)

  5519         apply clarsimp

  5520         apply (frule subsetD [OF D \<subseteq> ?C, THEN f_inv_into_f])

  5521         apply (erule rev_bexI, fast)

  5522         done

  5523     qed

  5524     then show "\<exists>D\<subseteq>C. finite D \<and> S \<subseteq> \<Union>D" ..

  5525   qed

  5526 qed

  5527

  5528 lemma connected_continuous_image:

  5529   assumes "continuous_on s f"

  5530     and "connected s"

  5531   shows "connected(f  s)"

  5532 proof -

  5533   {

  5534     fix T

  5535     assume as:

  5536       "T \<noteq> {}"

  5537       "T \<noteq> f  s"

  5538       "openin (subtopology euclidean (f  s)) T"

  5539       "closedin (subtopology euclidean (f  s)) T"

  5540     have "{x \<in> s. f x \<in> T} = {} \<or> {x \<in> s. f x \<in> T} = s"

  5541       using assms(1)[unfolded continuous_on_open, THEN spec[where x=T]]

  5542       using assms(1)[unfolded continuous_on_closed, THEN spec[where x=T]]

  5543       using assms(2)[unfolded connected_clopen, THEN spec[where x="{x \<in> s. f x \<in> T}"]] as(3,4) by auto

  5544     then have False using as(1,2)

  5545       using as(4)[unfolded closedin_def topspace_euclidean_subtopology] by auto

  5546   }

  5547   then show ?thesis

  5548     unfolding connected_clopen by auto

  5549 qed

  5550

  5551 text {* Continuity implies uniform continuity on a compact domain. *}

  5552

  5553 lemma compact_uniformly_continuous:

  5554   assumes f: "continuous_on s f"

  5555     and s: "compact s"

  5556   shows "uniformly_continuous_on s f"

  5557   unfolding uniformly_continuous_on_def

  5558 proof (cases, safe)

  5559   fix e :: real

  5560   assume "0 < e" "s \<noteq> {}"

  5561   def [simp]: R \<equiv> "{(y, d). y \<in> s \<and> 0 < d \<and> ball y d \<inter> s \<subseteq> {x \<in> s. f x \<in> ball (f y) (e/2) } }"

  5562   let ?b = "(\<lambda>(y, d). ball y (d/2))"

  5563   have "(\<forall>r\<in>R. open (?b r))" "s \<subseteq> (\<Union>r\<in>R. ?b r)"

  5564   proof safe

  5565     fix y

  5566     assume "y \<in> s"

  5567     from continuous_open_in_preimage[OF f open_ball]

  5568     obtain T where "open T" and T: "{x \<in> s. f x \<in> ball (f y) (e/2)} = T \<inter> s"

  5569       unfolding openin_subtopology open_openin by metis

  5570     then obtain d where "ball y d \<subseteq> T" "0 < d"

  5571       using 0 < e y \<in> s by (auto elim!: openE)

  5572     with T y \<in> s show "y \<in> (\<Union>r\<in>R. ?b r)"

  5573       by (intro UN_I[of "(y, d)"]) auto

  5574   qed auto

  5575   with s obtain D where D: "finite D" "D \<subseteq> R" "s \<subseteq> (\<Union>(y, d)\<in>D. ball y (d/2))"

  5576     by (rule compactE_image)

  5577   with s \<noteq> {} have [simp]: "\<And>x. x < Min (snd  D) \<longleftrightarrow> (\<forall>(y, d)\<in>D. x < d)"

  5578     by (subst Min_gr_iff) auto

  5579   show "\<exists>d>0. \<forall>x\<in>s. \<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist (f x') (f x) < e"

  5580   proof (rule, safe)

  5581     fix x x'

  5582     assume in_s: "x' \<in> s" "x \<in> s"

  5583     with D obtain y d where x: "x \<in> ball y (d/2)" "(y, d) \<in> D"

  5584       by blast

  5585     moreover assume "dist x x' < Min (sndD) / 2"

  5586     ultimately have "dist y x' < d"

  5587       by (intro dist_double[where x=x and d=d]) (auto simp: dist_commute)

  5588     with D x in_s show  "dist (f x) (f x') < e"

  5589       by (intro dist_double[where x="f y" and d=e]) (auto simp: dist_commute subset_eq)

  5590   qed (insert D, auto)

  5591 qed auto

  5592

  5593 text {* A uniformly convergent limit of continuous functions is continuous. *}

  5594

  5595 lemma continuous_uniform_limit:

  5596   fixes f :: "'a \<Rightarrow> 'b::metric_space \<Rightarrow> 'c::metric_space"

  5597   assumes "\<not> trivial_limit F"

  5598     and "eventually (\<lambda>n. continuous_on s (f n)) F"

  5599     and "\<forall>e>0. eventually (\<lambda>n. \<forall>x\<in>s. dist (f n x) (g x) < e) F"

  5600   shows "continuous_on s g"

  5601 proof -

  5602   {

  5603     fix x and e :: real

  5604     assume "x\<in>s" "e>0"

  5605     have "eventually (\<lambda>n. \<forall>x\<in>s. dist (f n x) (g x) < e / 3) F"

  5606       using e>0 assms(3)[THEN spec[where x="e/3"]] by auto

  5607     from eventually_happens [OF eventually_conj [OF this assms(2)]]

  5608     obtain n where n:"\<forall>x\<in>s. dist (f n x) (g x) < e / 3"  "continuous_on s (f n)"

  5609       using assms(1) by blast

  5610     have "e / 3 > 0" using e>0 by auto

  5611     then obtain d where "d>0" and d:"\<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist (f n x') (f n x) < e / 3"

  5612       using n(2)[unfolded continuous_on_iff, THEN bspec[where x=x], OF x\<in>s, THEN spec[where x="e/3"]] by blast

  5613     {

  5614       fix y

  5615       assume "y \<in> s" and "dist y x < d"

  5616       then have "dist (f n y) (f n x) < e / 3"

  5617         by (rule d [rule_format])

  5618       then have "dist (f n y) (g x) < 2 * e / 3"

  5619         using dist_triangle [of "f n y" "g x" "f n x"]

  5620         using n(1)[THEN bspec[where x=x], OF x\<in>s]

  5621         by auto

  5622       then have "dist (g y) (g x) < e"

  5623         using n(1)[THEN bspec[where x=y], OF y\<in>s]

  5624         using dist_triangle3 [of "g y" "g x" "f n y"]

  5625         by auto

  5626     }

  5627     then have "\<exists>d>0. \<forall>x'\<in>s. dist x' x < d \<longrightarrow> dist (g x') (g x) < e"

  5628       using d>0 by auto

  5629   }

  5630   then show ?thesis

  5631     unfolding continuous_on_iff by auto

  5632 qed

  5633

  5634

  5635 subsection {* Topological stuff lifted from and dropped to R *}

  5636

  5637 lemma open_real:

  5638   fixes s :: "real set"

  5639   shows "open s \<longleftrightarrow> (\<forall>x \<in> s. \<exists>e>0. \<forall>x'. abs(x' - x) < e --> x' \<in> s)"

  5640   unfolding open_dist dist_norm by simp

  5641

  5642 lemma islimpt_approachable_real:

  5643   fixes s :: "real set"

  5644   shows "x islimpt s \<longleftrightarrow> (\<forall>e>0.  \<exists>x'\<in> s. x' \<noteq> x \<and> abs(x' - x) < e)"

  5645   unfolding islimpt_approachable dist_norm by simp

  5646

  5647 lemma closed_real:

  5648   fixes s :: "real set"

  5649   shows "closed s \<longleftrightarrow> (\<forall>x. (\<forall>e>0.  \<exists>x' \<in> s. x' \<noteq> x \<and> abs(x' - x) < e) \<longrightarrow> x \<in> s)"

  5650   unfolding closed_limpt islimpt_approachable dist_norm by simp

  5651

  5652 lemma continuous_at_real_range:

  5653   fixes f :: "'a::real_normed_vector \<Rightarrow> real"

  5654   shows "continuous (at x) f \<longleftrightarrow> (\<forall>e>0. \<exists>d>0. \<forall>x'. norm(x' - x) < d --> abs(f x' - f x) < e)"

  5655   unfolding continuous_at

  5656   unfolding Lim_at

  5657   unfolding dist_nz[symmetric]

  5658   unfolding dist_norm

  5659   apply auto

  5660   apply (erule_tac x=e in allE)

  5661   apply auto

  5662   apply (rule_tac x=d in exI)

  5663   apply auto

  5664   apply (erule_tac x=x' in allE)

  5665   apply auto

  5666   apply (erule_tac x=e in allE)

  5667   apply auto

  5668   done

  5669

  5670 lemma continuous_on_real_range:

  5671   fixes f :: "'a::real_normed_vector \<Rightarrow> real"

  5672   shows "continuous_on s f \<longleftrightarrow>

  5673     (\<forall>x \<in> s. \<forall>e>0. \<exists>d>0. (\<forall>x' \<in> s. norm(x' - x) < d \<longrightarrow> abs(f x' - f x) < e))"

  5674   unfolding continuous_on_iff dist_norm by simp

  5675

  5676 text {* Hence some handy theorems on distance, diameter etc. of/from a set. *}

  5677

  5678 lemma distance_attains_sup:

  5679   assumes "compact s" "s \<noteq> {}"

  5680   shows "\<exists>x\<in>s. \<forall>y\<in>s. dist a y \<le> dist a x"

  5681 proof (rule continuous_attains_sup [OF assms])

  5682   {

  5683     fix x

  5684     assume "x\<in>s"

  5685     have "(dist a ---> dist a x) (at x within s)"

  5686       by (intro tendsto_dist tendsto_const tendsto_ident_at)

  5687   }

  5688   then show "continuous_on s (dist a)"

  5689     unfolding continuous_on ..

  5690 qed

  5691

  5692 text {* For \emph{minimal} distance, we only need closure, not compactness. *}

  5693

  5694 lemma distance_attains_inf:

  5695   fixes a :: "'a::heine_borel"

  5696   assumes "closed s"

  5697     and "s \<noteq> {}"

  5698   shows "\<exists>x\<in>s. \<forall>y\<in>s. dist a x \<le> dist a y"

  5699 proof -

  5700   from assms(2) obtain b where "b \<in> s" by auto

  5701   let ?B = "s \<inter> cball a (dist b a)"

  5702   have "?B \<noteq> {}" using b \<in> s

  5703     by (auto simp add: dist_commute)

  5704   moreover have "continuous_on ?B (dist a)"

  5705     by (auto intro!: continuous_at_imp_continuous_on continuous_dist continuous_at_id continuous_const)

  5706   moreover have "compact ?B"

  5707     by (intro closed_inter_compact closed s compact_cball)

  5708   ultimately obtain x where "x \<in> ?B" "\<forall>y\<in>?B. dist a x \<le> dist a y"

  5709     by (metis continuous_attains_inf)

  5710   then show ?thesis by fastforce

  5711 qed

  5712

  5713

  5714 subsection {* Pasted sets *}

  5715

  5716 lemma bounded_Times:

  5717   assumes "bounded s" "bounded t"

  5718   shows "bounded (s \<times> t)"

  5719 proof -

  5720   obtain x y a b where "\<forall>z\<in>s. dist x z \<le> a" "\<forall>z\<in>t. dist y z \<le> b"

  5721     using assms [unfolded bounded_def] by auto

  5722   then have "\<forall>z\<in>s \<times> t. dist (x, y) z \<le> sqrt (a\<^sup>2 + b\<^sup>2)"

  5723     by (auto simp add: dist_Pair_Pair real_sqrt_le_mono add_mono power_mono)

  5724   then show ?thesis unfolding bounded_any_center [where a="(x, y)"] by auto

  5725 qed

  5726

  5727 lemma mem_Times_iff: "x \<in> A \<times> B \<longleftrightarrow> fst x \<in> A \<and> snd x \<in> B"

  5728   by (induct x) simp

  5729

  5730 lemma seq_compact_Times: "seq_compact s \<Longrightarrow> seq_compact t \<Longrightarrow> seq_compact (s \<times> t)"

  5731   unfolding seq_compact_def

  5732   apply clarify

  5733   apply (drule_tac x="fst \<circ> f" in spec)

  5734   apply (drule mp, simp add: mem_Times_iff)

  5735   apply (clarify, rename_tac l1 r1)

  5736   apply (drule_tac x="snd \<circ> f \<circ> r1" in spec)

  5737   apply (drule mp, simp add: mem_Times_iff)

  5738   apply (clarify, rename_tac l2 r2)

  5739   apply (rule_tac x="(l1, l2)" in rev_bexI, simp)

  5740   apply (rule_tac x="r1 \<circ> r2" in exI)

  5741   apply (rule conjI, simp add: subseq_def)

  5742   apply (drule_tac f=r2 in LIMSEQ_subseq_LIMSEQ, assumption)

  5743   apply (drule (1) tendsto_Pair) back

  5744   apply (simp add: o_def)

  5745   done

  5746

  5747 lemma compact_Times:

  5748   assumes "compact s" "compact t"

  5749   shows "compact (s \<times> t)"

  5750 proof (rule compactI)

  5751   fix C

  5752   assume C: "\<forall>t\<in>C. open t" "s \<times> t \<subseteq> \<Union>C"

  5753   have "\<forall>x\<in>s. \<exists>a. open a \<and> x \<in> a \<and> (\<exists>d\<subseteq>C. finite d \<and> a \<times> t \<subseteq> \<Union>d)"

  5754   proof

  5755     fix x

  5756     assume "x \<in> s"

  5757     have "\<forall>y\<in>t. \<exists>a b c. c \<in> C \<and> open a \<and> open b \<and> x \<in> a \<and> y \<in> b \<and> a \<times> b \<subseteq> c" (is "\<forall>y\<in>t. ?P y")

  5758     proof

  5759       fix y

  5760       assume "y \<in> t"

  5761       with x \<in> s C obtain c where "c \<in> C" "(x, y) \<in> c" "open c" by auto

  5762       then show "?P y" by (auto elim!: open_prod_elim)

  5763     qed

  5764     then obtain a b c where b: "\<And>y. y \<in> t \<Longrightarrow> open (b y)"

  5765       and c: "\<And>y. y \<in> t \<Longrightarrow> c y \<in> C \<and> open (a y) \<and> open (b y) \<and> x \<in> a y \<and> y \<in> b y \<and> a y \<times> b y \<subseteq> c y"

  5766       by metis

  5767     then have "\<forall>y\<in>t. open (b y)" "t \<subseteq> (\<Union>y\<in>t. b y)" by auto

  5768     from compactE_image[OF compact t this] obtain D where D: "D \<subseteq> t" "finite D" "t \<subseteq> (\<Union>y\<in>D. b y)"

  5769       by auto

  5770     moreover from D c have "(\<Inter>y\<in>D. a y) \<times> t \<subseteq> (\<Union>y\<in>D. c y)"

  5771       by (fastforce simp: subset_eq)

  5772     ultimately show "\<exists>a. open a \<and> x \<in> a \<and> (\<exists>d\<subseteq>C. finite d \<and> a \<times> t \<subseteq> \<Union>d)"

  5773       using c by (intro exI[of _ "cD"] exI[of _ "\<Inter>(aD)"] conjI) (auto intro!: open_INT)

  5774   qed

  5775   then obtain a d where a: "\<forall>x\<in>s. open (a x)" "s \<subseteq> (\<Union>x\<in>s. a x)"

  5776     and d: "\<And>x. x \<in> s \<Longrightarrow> d x \<subseteq> C \<and> finite (d x) \<and> a x \<times> t \<subseteq> \<Union>d x"

  5777     unfolding subset_eq UN_iff by metis

  5778   moreover

  5779   from compactE_image[OF compact s a]

  5780   obtain e where e: "e \<subseteq> s" "finite e" and s: "s \<subseteq> (\<Union>x\<in>e. a x)"

  5781     by auto

  5782   moreover

  5783   {

  5784     from s have "s \<times> t \<subseteq> (\<Union>x\<in>e. a x \<times> t)"

  5785       by auto

  5786     also have "\<dots> \<subseteq> (\<Union>x\<in>e. \<Union>d x)"

  5787       using d e \<subseteq> s by (intro UN_mono) auto

  5788     finally have "s \<times> t \<subseteq> (\<Union>x\<in>e. \<Union>d x)" .

  5789   }

  5790   ultimately show "\<exists>C'\<subseteq>C. finite C' \<and> s \<times> t \<subseteq> \<Union>C'"

  5791     by (intro exI[of _ "(\<Union>x\<in>e. d x)"]) (auto simp add: subset_eq)

  5792 qed

  5793

  5794 text{* Hence some useful properties follow quite easily. *}

  5795

  5796 lemma compact_scaling:

  5797   fixes s :: "'a::real_normed_vector set"

  5798   assumes "compact s"

  5799   shows "compact ((\<lambda>x. c *\<^sub>R x)  s)"

  5800 proof -

  5801   let ?f = "\<lambda>x. scaleR c x"

  5802   have *: "bounded_linear ?f" by (rule bounded_linear_scaleR_right)

  5803   show ?thesis

  5804     using compact_continuous_image[of s ?f] continuous_at_imp_continuous_on[of s ?f]

  5805     using linear_continuous_at[OF *] assms

  5806     by auto

  5807 qed

  5808

  5809 lemma compact_negations:

  5810   fixes s :: "'a::real_normed_vector set"

  5811   assumes "compact s"

  5812   shows "compact ((\<lambda>x. - x)  s)"

  5813   using compact_scaling [OF assms, of "- 1"] by auto

  5814

  5815 lemma compact_sums:

  5816   fixes s t :: "'a::real_normed_vector set"

  5817   assumes "compact s"

  5818     and "compact t"

  5819   shows "compact {x + y | x y. x \<in> s \<and> y \<in> t}"

  5820 proof -

  5821   have *: "{x + y | x y. x \<in> s \<and> y \<in> t} = (\<lambda>z. fst z + snd z)  (s \<times> t)"

  5822     apply auto

  5823     unfolding image_iff

  5824     apply (rule_tac x="(xa, y)" in bexI)

  5825     apply auto

  5826     done

  5827   have "continuous_on (s \<times> t) (\<lambda>z. fst z + snd z)"

  5828     unfolding continuous_on by (rule ballI) (intro tendsto_intros)

  5829   then show ?thesis

  5830     unfolding * using compact_continuous_image compact_Times [OF assms] by auto

  5831 qed

  5832

  5833 lemma compact_differences:

  5834   fixes s t :: "'a::real_normed_vector set"

  5835   assumes "compact s"

  5836     and "compact t"

  5837   shows "compact {x - y | x y. x \<in> s \<and> y \<in> t}"

  5838 proof-

  5839   have "{x - y | x y. x\<in>s \<and> y \<in> t} =  {x + y | x y. x \<in> s \<and> y \<in> (uminus  t)}"

  5840     apply auto

  5841     apply (rule_tac x= xa in exI)

  5842     apply auto

  5843     done

  5844   then show ?thesis

  5845     using compact_sums[OF assms(1) compact_negations[OF assms(2)]] by auto

  5846 qed

  5847

  5848 lemma compact_translation:

  5849   fixes s :: "'a::real_normed_vector set"

  5850   assumes "compact s"

  5851   shows "compact ((\<lambda>x. a + x)  s)"

  5852 proof -

  5853   have "{x + y |x y. x \<in> s \<and> y \<in> {a}} = (\<lambda>x. a + x)  s"

  5854     by auto

  5855   then show ?thesis

  5856     using compact_sums[OF assms compact_sing[of a]] by auto

  5857 qed

  5858

  5859 lemma compact_affinity:

  5860   fixes s :: "'a::real_normed_vector set"

  5861   assumes "compact s"

  5862   shows "compact ((\<lambda>x. a + c *\<^sub>R x)  s)"

  5863 proof -

  5864   have "op + a  op *\<^sub>R c  s = (\<lambda>x. a + c *\<^sub>R x)  s"

  5865     by auto

  5866   then show ?thesis

  5867     using compact_translation[OF compact_scaling[OF assms], of a c] by auto

  5868 qed

  5869

  5870 text {* Hence we get the following. *}

  5871

  5872 lemma compact_sup_maxdistance:

  5873   fixes s :: "'a::metric_space set"

  5874   assumes "compact s"

  5875     and "s \<noteq> {}"

  5876   shows "\<exists>x\<in>s. \<exists>y\<in>s. \<forall>u\<in>s. \<forall>v\<in>s. dist u v \<le> dist x y"

  5877 proof -

  5878   have "compact (s \<times> s)"

  5879     using compact s by (intro compact_Times)

  5880   moreover have "s \<times> s \<noteq> {}"

  5881     using s \<noteq> {} by auto

  5882   moreover have "continuous_on (s \<times> s) (\<lambda>x. dist (fst x) (snd x))"

  5883     by (intro continuous_at_imp_continuous_on ballI continuous_intros)

  5884   ultimately show ?thesis

  5885     using continuous_attains_sup[of "s \<times> s" "\<lambda>x. dist (fst x) (snd x)"] by auto

  5886 qed

  5887

  5888 text {* We can state this in terms of diameter of a set. *}

  5889

  5890 definition diameter :: "'a::metric_space set \<Rightarrow> real" where

  5891   "diameter S = (if S = {} then 0 else SUP (x,y):S\<times>S. dist x y)"

  5892

  5893 lemma diameter_bounded_bound:

  5894   fixes s :: "'a :: metric_space set"

  5895   assumes s: "bounded s" "x \<in> s" "y \<in> s"

  5896   shows "dist x y \<le> diameter s"

  5897 proof -

  5898   from s obtain z d where z: "\<And>x. x \<in> s \<Longrightarrow> dist z x \<le> d"

  5899     unfolding bounded_def by auto

  5900   have "bdd_above (split dist  (s\<times>s))"

  5901   proof (intro bdd_aboveI, safe)

  5902     fix a b

  5903     assume "a \<in> s" "b \<in> s"

  5904     with z[of a] z[of b] dist_triangle[of a b z]

  5905     show "dist a b \<le> 2 * d"

  5906       by (simp add: dist_commute)

  5907   qed

  5908   moreover have "(x,y) \<in> s\<times>s" using s by auto

  5909   ultimately have "dist x y \<le> (SUP (x,y):s\<times>s. dist x y)"

  5910     by (rule cSUP_upper2) simp

  5911   with x \<in> s show ?thesis

  5912     by (auto simp add: diameter_def)

  5913 qed

  5914

  5915 lemma diameter_lower_bounded:

  5916   fixes s :: "'a :: metric_space set"

  5917   assumes s: "bounded s"

  5918     and d: "0 < d" "d < diameter s"

  5919   shows "\<exists>x\<in>s. \<exists>y\<in>s. d < dist x y"

  5920 proof (rule ccontr)

  5921   assume contr: "\<not> ?thesis"

  5922   moreover have "s \<noteq> {}"

  5923     using d by (auto simp add: diameter_def)

  5924   ultimately have "diameter s \<le> d"

  5925     by (auto simp: not_less diameter_def intro!: cSUP_least)

  5926   with d < diameter s show False by auto

  5927 qed

  5928

  5929 lemma diameter_bounded:

  5930   assumes "bounded s"

  5931   shows "\<forall>x\<in>s. \<forall>y\<in>s. dist x y \<le> diameter s"

  5932     and "\<forall>d>0. d < diameter s \<longrightarrow> (\<exists>x\<in>s. \<exists>y\<in>s. dist x y > d)"

  5933   using diameter_bounded_bound[of s] diameter_lower_bounded[of s] assms

  5934   by auto

  5935

  5936 lemma diameter_compact_attained:

  5937   assumes "compact s"

  5938     and "s \<noteq> {}"

  5939   shows "\<exists>x\<in>s. \<exists>y\<in>s. dist x y = diameter s"

  5940 proof -

  5941   have b: "bounded s" using assms(1)

  5942     by (rule compact_imp_bounded)

  5943   then obtain x y where xys: "x\<in>s" "y\<in>s"

  5944     and xy: "\<forall>u\<in>s. \<forall>v\<in>s. dist u v \<le> dist x y"

  5945     using compact_sup_maxdistance[OF assms] by auto

  5946   then have "diameter s \<le> dist x y"

  5947     unfolding diameter_def

  5948     apply clarsimp

  5949     apply (rule cSUP_least)

  5950     apply fast+

  5951     done

  5952   then show ?thesis

  5953     by (metis b diameter_bounded_bound order_antisym xys)

  5954 qed

  5955

  5956 text {* Related results with closure as the conclusion. *}

  5957

  5958 lemma closed_scaling:

  5959   fixes s :: "'a::real_normed_vector set"

  5960   assumes "closed s"

  5961   shows "closed ((\<lambda>x. c *\<^sub>R x)  s)"

  5962 proof (cases "c = 0")

  5963   case True then show ?thesis

  5964     by (auto simp add: image_constant_conv)

  5965 next

  5966   case False

  5967   from assms have "closed ((\<lambda>x. inverse c *\<^sub>R x) - s)"

  5968     by (simp add: continuous_closed_vimage)

  5969   also have "(\<lambda>x. inverse c *\<^sub>R x) - s = (\<lambda>x. c *\<^sub>R x)  s"

  5970     using c \<noteq> 0 by (auto elim: image_eqI [rotated])

  5971   finally show ?thesis .

  5972 qed

  5973

  5974 lemma closed_negations:

  5975   fixes s :: "'a::real_normed_vector set"

  5976   assumes "closed s"

  5977   shows "closed ((\<lambda>x. -x)  s)"

  5978   using closed_scaling[OF assms, of "- 1"] by simp

  5979

  5980 lemma compact_closed_sums:

  5981   fixes s :: "'a::real_normed_vector set"

  5982   assumes "compact s" and "closed t"

  5983   shows "closed {x + y | x y. x \<in> s \<and> y \<in> t}"

  5984 proof -

  5985   let ?S = "{x + y |x y. x \<in> s \<and> y \<in> t}"

  5986   {

  5987     fix x l

  5988     assume as: "\<forall>n. x n \<in> ?S"  "(x ---> l) sequentially"

  5989     from as(1) obtain f where f: "\<forall>n. x n = fst (f n) + snd (f n)"  "\<forall>n. fst (f n) \<in> s"  "\<forall>n. snd (f n) \<in> t"

  5990       using choice[of "\<lambda>n y. x n = (fst y) + (snd y) \<and> fst y \<in> s \<and> snd y \<in> t"] by auto

  5991     obtain l' r where "l'\<in>s" and r: "subseq r" and lr: "(((\<lambda>n. fst (f n)) \<circ> r) ---> l') sequentially"

  5992       using assms(1)[unfolded compact_def, THEN spec[where x="\<lambda> n. fst (f n)"]] using f(2) by auto

  5993     have "((\<lambda>n. snd (f (r n))) ---> l - l') sequentially"

  5994       using tendsto_diff[OF LIMSEQ_subseq_LIMSEQ[OF as(2) r] lr] and f(1)

  5995       unfolding o_def

  5996       by auto

  5997     then have "l - l' \<in> t"

  5998       using assms(2)[unfolded closed_sequential_limits,

  5999         THEN spec[where x="\<lambda> n. snd (f (r n))"],

  6000         THEN spec[where x="l - l'"]]

  6001       using f(3)

  6002       by auto

  6003     then have "l \<in> ?S"

  6004       using l' \<in> s

  6005       apply auto

  6006       apply (rule_tac x=l' in exI)

  6007       apply (rule_tac x="l - l'" in exI)

  6008       apply auto

  6009       done

  6010   }

  6011   then show ?thesis

  6012     unfolding closed_sequential_limits by fast

  6013 qed

  6014

  6015 lemma closed_compact_sums:

  6016   fixes s t :: "'a::real_normed_vector set"

  6017   assumes "closed s"

  6018     and "c`