author paulson Tue May 01 23:25:00 2018 +0100 (12 months ago) changeset 68062 ee88c0fccbae parent 68060 3931ed905e93 child 68063 539048827fe8
simplified some messy proofs
```     1.1 --- a/src/HOL/Analysis/Cartesian_Euclidean_Space.thy	Tue May 01 16:42:14 2018 +0200
1.2 +++ b/src/HOL/Analysis/Cartesian_Euclidean_Space.thy	Tue May 01 23:25:00 2018 +0100
1.3 @@ -1956,7 +1956,7 @@
1.4    done
1.5
1.6  lemma bounded_linear_component_cart[intro]: "bounded_linear (\<lambda>x::real^'n. x \$ k)"
1.7 -  apply (rule bounded_linearI[where K=1])
1.8 +  apply (rule bounded_linear_intro[where K=1])
1.9    using component_le_norm_cart[of _ k] unfolding real_norm_def by auto
1.10
1.11  lemma interval_split_cart:
```
```     2.1 --- a/src/HOL/Analysis/Linear_Algebra.thy	Tue May 01 16:42:14 2018 +0200
2.2 +++ b/src/HOL/Analysis/Linear_Algebra.thy	Tue May 01 23:25:00 2018 +0100
2.3 @@ -27,13 +27,6 @@
2.4    show "f (s *\<^sub>R v) = s *\<^sub>R (f v)" by (rule f.scaleR)
2.5  qed
2.6
2.7 -lemma bounded_linearI:
2.8 -  assumes "\<And>x y. f (x + y) = f x + f y"
2.9 -    and "\<And>r x. f (r *\<^sub>R x) = r *\<^sub>R f x"
2.10 -    and "\<And>x. norm (f x) \<le> norm x * K"
2.11 -  shows "bounded_linear f"
2.12 -  using assms by (rule bounded_linear_intro) (* FIXME: duplicate *)
2.13 -
2.14  subsection \<open>A generic notion of "hull" (convex, affine, conic hull and closure).\<close>
2.15
2.16  definition%important hull :: "('a set \<Rightarrow> bool) \<Rightarrow> 'a set \<Rightarrow> 'a set"  (infixl "hull" 75)
2.17 @@ -2514,35 +2507,27 @@
2.18      and fx: "f x = 0"
2.19    shows "x = 0"
2.20    using fB ifB fi xsB fx
2.21 -proof (induct arbitrary: x rule: finite_induct[OF fB])
2.22 -  case 1
2.23 +proof (induction B arbitrary: x rule: finite_induct)
2.24 +  case empty
2.25    then show ?case by auto
2.26  next
2.27 -  case (2 a b x)
2.28 -  have fb: "finite b" using "2.prems" by simp
2.29 +  case (insert a b x)
2.30    have th0: "f ` b \<subseteq> f ` (insert a b)"
2.31 -    apply (rule image_mono)
2.32 -    apply blast
2.33 -    done
2.34 -  from independent_mono[ OF "2.prems"(2) th0]
2.35 -  have ifb: "independent (f ` b)"  .
2.36 +    by (simp add: subset_insertI)
2.37 +  have ifb: "independent (f ` b)"
2.38 +    using independent_mono insert.prems(1) th0 by blast
2.39    have fib: "inj_on f b"
2.40 -    apply (rule subset_inj_on [OF "2.prems"(3)])
2.41 -    apply blast
2.42 -    done
2.43 -  from span_breakdown[of a "insert a b", simplified, OF "2.prems"(4)]
2.44 +    using insert.prems(2) by blast
2.45 +  from span_breakdown[of a "insert a b", simplified, OF insert.prems(3)]
2.46    obtain k where k: "x - k*\<^sub>R a \<in> span (b - {a})"
2.47      by blast
2.48    have "f (x - k*\<^sub>R a) \<in> span (f ` b)"
2.49      unfolding span_linear_image[OF lf]
2.50 -    apply (rule imageI)
2.51 -    using k span_mono[of "b - {a}" b]
2.52 -    apply blast
2.53 -    done
2.54 +    using "insert.hyps"(2) k by auto
2.55    then have "f x - k*\<^sub>R f a \<in> span (f ` b)"
2.56      by (simp add: linear_diff[OF lf] linear_cmul[OF lf])
2.57    then have th: "-k *\<^sub>R f a \<in> span (f ` b)"
2.58 -    using "2.prems"(5) by simp
2.59 +    using insert.prems(4) by simp
2.60    have xsb: "x \<in> span b"
2.61    proof (cases "k = 0")
2.62      case True
2.63 @@ -2551,19 +2536,18 @@
2.64        by blast
2.65    next
2.66      case False
2.67 -    with span_mul[OF th, of "- 1/ k"]
2.68 -    have th1: "f a \<in> span (f ` b)"
2.69 -      by auto
2.70 -    from inj_on_image_set_diff[OF "2.prems"(3), of "insert a b " "{a}", symmetric]
2.71 -    have tha: "f ` insert a b - f ` {a} = f ` (insert a b - {a})" by blast
2.72 -    from "2.prems"(2) [unfolded dependent_def bex_simps(8), rule_format, of "f a"]
2.73 -    have "f a \<notin> span (f ` b)" using tha
2.74 -      using "2.hyps"(2)
2.75 -      "2.prems"(3) by auto
2.76 -    with th1 have False by blast
2.77 +    from inj_on_image_set_diff[OF insert.prems(2), of "insert a b " "{a}", symmetric]
2.78 +    have "f ` insert a b - f ` {a} = f ` (insert a b - {a})" by blast
2.79 +    then have "f a \<notin> span (f ` b)"
2.80 +      using dependent_def insert.hyps(2) insert.prems(1) by fastforce
2.81 +    moreover have "f a \<in> span (f ` b)"
2.82 +      using False span_mul[OF th, of "- 1/ k"] by auto
2.83 +    ultimately have False
2.84 +      by blast
2.85      then show ?thesis by blast
2.86    qed
2.87 -  from "2.hyps"(3)[OF fb ifb fib xsb "2.prems"(5)] show "x = 0" .
2.88 +  show "x = 0"
2.89 +    using ifb fib xsb insert.IH insert.prems(4) by blast
2.90  qed
2.91
2.92  text \<open>Can construct an isomorphism between spaces of same dimension.\<close>
2.93 @@ -2644,9 +2628,8 @@
2.94    let ?P = "{x. \<forall>y\<in> span C. f x y = g x y}"
2.95    from bf bg have sp: "subspace ?P"
2.96      unfolding bilinear_def linear_iff subspace_def bf bg
2.97 -    by (auto simp add: span_0 bilinear_lzero[OF bf] bilinear_lzero[OF bg] span_add Ball_def
2.98 +    by (auto simp add: bilinear_lzero[OF bf] bilinear_lzero[OF bg] span_add
2.99        intro: bilinear_ladd[OF bf])
2.100 -
2.101    have sfg: "\<And>x. x \<in> B \<Longrightarrow> subspace {a. f x a = g x a}"
2.102      apply (auto simp add: subspace_def)
2.103      using bf bg unfolding bilinear_def linear_iff
2.104 @@ -2655,10 +2638,7 @@
2.105      done
2.106    have "\<forall>y\<in> span C. f x y = g x y" if "x \<in> span B" for x
2.107      apply (rule span_induct [OF that sp])
2.108 -    apply (rule ballI)
2.109 -    apply (erule span_induct)
2.110 -    apply (simp_all add: sfg fg)
2.111 -    done
2.112 +    using fg sfg span_induct by blast
2.113    then show ?thesis
2.114      using SB TC assms by auto
2.115  qed
2.116 @@ -2707,11 +2687,8 @@
2.117    (is "?lhs \<longleftrightarrow> ?rhs")
2.118  proof
2.119    assume h: "?lhs"
2.120 -  {
2.121 -    fix x y
2.122 -    assume x: "x \<in> S"
2.123 -    assume y: "y \<in> S"
2.124 -    assume f: "f x = f y"
2.125 +  { fix x y
2.126 +    assume x: "x \<in> S" and y: "y \<in> S" and f: "f x = f y"
2.127      from x fS have S0: "card S \<noteq> 0"
2.128        by auto
2.129      have "x = y"
2.130 @@ -2719,15 +2696,13 @@
2.131        assume xy: "\<not> ?thesis"
2.132        have th: "card S \<le> card (f ` (S - {y}))"
2.133          unfolding c
2.134 -        apply (rule card_mono)
2.135 -        apply (rule finite_imageI)
2.136 -        using fS apply simp
2.137 -        using h xy x y f unfolding subset_eq image_iff
2.138 -        apply auto
2.139 -        apply (case_tac "xa = f x")
2.140 -        apply (rule bexI[where x=x])
2.141 -        apply auto
2.142 -        done
2.143 +      proof (rule card_mono)
2.144 +        show "finite (f ` (S - {y}))"
2.145 +          by (simp add: fS)
2.146 +        show "T \<subseteq> f ` (S - {y})"
2.147 +          using h xy x y f unfolding subset_eq image_iff
2.148 +          by (metis member_remove remove_def)
2.149 +      qed
2.150        also have " \<dots> \<le> card (S - {y})"
2.151          apply (rule card_image_le)
2.152          using fS by simp
2.153 @@ -2740,17 +2715,13 @@
2.154  next
2.155    assume h: ?rhs
2.156    have "f ` S = T"
2.157 -    apply (rule card_subset_eq[OF fT ST])
2.158 -    unfolding card_image[OF h]
2.159 -    apply (rule c)
2.160 -    done
2.161 +    by (simp add: ST c card_image card_subset_eq fT h)
2.162    then show ?lhs by blast
2.163  qed
2.164
2.165  lemma linear_surjective_imp_injective:
2.166    fixes f :: "'a::euclidean_space \<Rightarrow> 'a::euclidean_space"
2.167 -  assumes lf: "linear f"
2.168 -    and sf: "surj f"
2.169 +  assumes lf: "linear f" and sf: "surj f"
2.170    shows "inj f"
2.171  proof -
2.172    let ?U = "UNIV :: 'a set"
2.173 @@ -2759,46 +2730,29 @@
2.174      by blast
2.175    {
2.176      fix x
2.177 -    assume x: "x \<in> span B"
2.178 -    assume fx: "f x = 0"
2.179 +    assume x: "x \<in> span B" and fx: "f x = 0"
2.180      from B(2) have fB: "finite B"
2.181        using independent_bound by auto
2.182 +    have Uspan: "UNIV \<subseteq> span (f ` B)"
2.183 +      by (simp add: B(3) lf sf spanning_surjective_image)
2.184      have fBi: "independent (f ` B)"
2.185 -      apply (rule card_le_dim_spanning[of "f ` B" ?U])
2.186 -      apply blast
2.187 -      using sf B(3)
2.188 -      unfolding span_linear_image[OF lf] surj_def subset_eq image_iff
2.189 -      apply blast
2.190 -      using fB apply blast
2.191 -      unfolding d[symmetric]
2.192 -      apply (rule card_image_le)
2.193 -      apply (rule fB)
2.194 -      done
2.195 +    proof (rule card_le_dim_spanning)
2.196 +      show "card (f ` B) \<le> dim ?U"
2.197 +        using card_image_le d fB by fastforce
2.198 +    qed (use fB Uspan in auto)
2.199      have th0: "dim ?U \<le> card (f ` B)"
2.200 -      apply (rule span_card_ge_dim)
2.201 -      apply blast
2.202 -      unfolding span_linear_image[OF lf]
2.203 -      apply (rule subset_trans[where B = "f ` UNIV"])
2.204 -      using sf unfolding surj_def
2.205 -      apply blast
2.206 -      apply (rule image_mono)
2.207 -      apply (rule B(3))
2.208 -      apply (metis finite_imageI fB)
2.209 -      done
2.210 +      by (rule span_card_ge_dim) (use Uspan fB in auto)
2.211      moreover have "card (f ` B) \<le> card B"
2.212        by (rule card_image_le, rule fB)
2.213      ultimately have th1: "card B = card (f ` B)"
2.214        unfolding d by arith
2.215      have fiB: "inj_on f B"
2.216 -      unfolding surjective_iff_injective_gen[OF fB finite_imageI[OF fB] th1 subset_refl, symmetric]
2.217 -      by blast
2.218 +      by (simp add: eq_card_imp_inj_on fB th1)
2.219      from linear_indep_image_lemma[OF lf fB fBi fiB x] fx
2.220      have "x = 0" by blast
2.221    }
2.222    then show ?thesis
2.223 -    unfolding linear_injective_0[OF lf]
2.224 -    using B(3)
2.225 -    by blast
2.226 +    unfolding linear_injective_0[OF lf] using B(3) by blast
2.227  qed
2.228
2.229  text \<open>Hence either is enough for isomorphism.\<close>
2.230 @@ -2854,9 +2808,7 @@
2.231      assume lf: "linear f" "linear f'"
2.232      assume f: "f \<circ> f' = id"
2.233      from f have sf: "surj f"
2.234 -      apply (auto simp add: o_def id_def surj_def)
2.235 -      apply metis
2.236 -      done
2.237 +      by (auto simp add: o_def id_def surj_def) metis
2.238      from linear_surjective_isomorphism[OF lf(1) sf] lf f
2.239      have "f' \<circ> f = id"
2.240        unfolding fun_eq_iff o_def id_def by metis
2.241 @@ -2874,18 +2826,13 @@
2.242    shows "linear g"
2.243  proof -
2.244    from gf have fi: "inj f"
2.245 -    apply (auto simp add: inj_on_def o_def id_def fun_eq_iff)
2.246 -    apply metis
2.247 -    done
2.248 +    by (auto simp add: inj_on_def o_def id_def fun_eq_iff) metis
2.249    from linear_injective_isomorphism[OF lf fi]
2.250 -  obtain h :: "'a \<Rightarrow> 'a" where h: "linear h" "\<forall>x. h (f x) = x" "\<forall>x. f (h x) = x"
2.251 +  obtain h :: "'a \<Rightarrow> 'a" where "linear h" and h: "\<forall>x. h (f x) = x" "\<forall>x. f (h x) = x"
2.252      by blast
2.253    have "h = g"
2.254 -    apply (rule ext) using gf h(2,3)
2.255 -    apply (simp add: o_def id_def fun_eq_iff)
2.256 -    apply metis
2.257 -    done
2.258 -  with h(1) show ?thesis by blast
2.259 +    by (metis gf h isomorphism_expand left_right_inverse_eq)
2.260 +  with \<open>linear h\<close> show ?thesis by blast
2.261  qed
2.262
2.263  lemma inj_linear_imp_inv_linear:
2.264 @@ -2944,28 +2891,21 @@
2.265    by (simp add: infnorm_eq_0)
2.266
2.267  lemma infnorm_neg: "infnorm (- x) = infnorm x"
2.268 -  unfolding infnorm_def
2.269 -  apply (rule cong[of "Sup" "Sup"])
2.270 -  apply blast
2.271 -  apply auto
2.272 -  done
2.273 +  unfolding infnorm_def by simp
2.274
2.275  lemma infnorm_sub: "infnorm (x - y) = infnorm (y - x)"
2.276 -proof -
2.277 -  have "y - x = - (x - y)" by simp
2.278 -  then show ?thesis
2.279 -    by (metis infnorm_neg)
2.280 -qed
2.281 -
2.282 -lemma real_abs_sub_infnorm: "\<bar>infnorm x - infnorm y\<bar> \<le> infnorm (x - y)"
2.283 +  by (metis infnorm_neg minus_diff_eq)
2.284 +
2.285 +lemma absdiff_infnorm: "\<bar>infnorm x - infnorm y\<bar> \<le> infnorm (x - y)"
2.286  proof -
2.287 -  have th: "\<And>(nx::real) n ny. nx \<le> n + ny \<Longrightarrow> ny \<le> n + nx \<Longrightarrow> \<bar>nx - ny\<bar> \<le> n"
2.288 +  have *: "\<And>(nx::real) n ny. nx \<le> n + ny \<Longrightarrow> ny \<le> n + nx \<Longrightarrow> \<bar>nx - ny\<bar> \<le> n"
2.289      by arith
2.290 -  from infnorm_triangle[of "x - y" " y"] infnorm_triangle[of "x - y" "-x"]
2.291 -  have ths: "infnorm x \<le> infnorm (x - y) + infnorm y"
2.292 -    "infnorm y \<le> infnorm (x - y) + infnorm x"
2.293 -    by (simp_all add: field_simps infnorm_neg)
2.294 -  from th[OF ths] show ?thesis .
2.295 +  show ?thesis
2.296 +  proof (rule *)
2.297 +    from infnorm_triangle[of "x - y" " y"] infnorm_triangle[of "x - y" "-x"]
2.298 +    show "infnorm x \<le> infnorm (x - y) + infnorm y" "infnorm y \<le> infnorm (x - y) + infnorm x"
2.299 +      by (simp_all add: field_simps infnorm_neg)
2.300 +  qed
2.301  qed
2.302
2.303  lemma real_abs_infnorm: "\<bar>infnorm x\<bar> = infnorm x"
2.304 @@ -2980,8 +2920,7 @@
2.305    unfolding infnorm_Max
2.306  proof (safe intro!: Max_eqI)
2.307    let ?B = "(\<lambda>i. \<bar>x \<bullet> i\<bar>) ` Basis"
2.308 -  {
2.309 -    fix b :: 'a
2.310 +  { fix b :: 'a
2.311      assume "b \<in> Basis"
2.312      then show "\<bar>a *\<^sub>R x \<bullet> b\<bar> \<le> \<bar>a\<bar> * Max ?B"
2.313        by (simp add: abs_mult mult_left_mono)
2.314 @@ -3007,27 +2946,17 @@
2.315  lemma norm_le_infnorm:
2.316    fixes x :: "'a::euclidean_space"
2.317    shows "norm x \<le> sqrt DIM('a) * infnorm x"
2.318 -proof -
2.319 -  let ?d = "DIM('a)"
2.320 -  have "real ?d \<ge> 0"
2.321 -    by simp
2.322 -  then have d2: "(sqrt (real ?d))\<^sup>2 = real ?d"
2.323 -    by (auto intro: real_sqrt_pow2)
2.324 -  have th: "sqrt (real ?d) * infnorm x \<ge> 0"
2.325 +  unfolding norm_eq_sqrt_inner id_def
2.326 +proof (rule real_le_lsqrt[OF inner_ge_zero])
2.327 +  show "sqrt DIM('a) * infnorm x \<ge> 0"
2.328      by (simp add: zero_le_mult_iff infnorm_pos_le)
2.329 -  have th1: "x \<bullet> x \<le> (sqrt (real ?d) * infnorm x)\<^sup>2"
2.330 -    unfolding power_mult_distrib d2
2.331 -    apply (subst euclidean_inner)
2.332 -    apply (subst power2_abs[symmetric])
2.333 -    apply (rule order_trans[OF sum_bounded_above[where K="\<bar>infnorm x\<bar>\<^sup>2"]])
2.334 -    apply (auto simp add: power2_eq_square[symmetric])
2.335 -    apply (subst power2_abs[symmetric])
2.336 -    apply (rule power_mono)
2.337 -    apply (auto simp: infnorm_Max)
2.338 -    done
2.339 -  from real_le_lsqrt[OF inner_ge_zero th th1]
2.340 -  show ?thesis
2.341 -    unfolding norm_eq_sqrt_inner id_def .
2.342 +  have "x \<bullet> x \<le> (\<Sum>b\<in>Basis. x \<bullet> b * (x \<bullet> b))"
2.343 +    by (metis euclidean_inner order_refl)
2.344 +  also have "... \<le> DIM('a) * \<bar>infnorm x\<bar>\<^sup>2"
2.345 +    by (rule sum_bounded_above) (metis Basis_le_infnorm abs_le_square_iff power2_eq_square real_abs_infnorm)
2.346 +  also have "... \<le> (sqrt DIM('a) * infnorm x)\<^sup>2"
2.347 +    by (simp add: power_mult_distrib)
2.348 +  finally show "x \<bullet> x \<le> (sqrt DIM('a) * infnorm x)\<^sup>2" .
2.349  qed
2.350
2.351  lemma tendsto_infnorm [tendsto_intros]:
2.352 @@ -3037,46 +2966,30 @@
2.353    fix r :: real
2.354    assume "r > 0"
2.355    then show "\<exists>s>0. \<forall>x. x \<noteq> a \<and> norm (x - a) < s \<longrightarrow> norm (infnorm x - infnorm a) < r"
2.356 -    by (metis real_norm_def le_less_trans real_abs_sub_infnorm infnorm_le_norm)
2.357 +    by (metis real_norm_def le_less_trans absdiff_infnorm infnorm_le_norm)
2.358  qed
2.359
2.360  text \<open>Equality in Cauchy-Schwarz and triangle inequalities.\<close>
2.361
2.362  lemma norm_cauchy_schwarz_eq: "x \<bullet> y = norm x * norm y \<longleftrightarrow> norm x *\<^sub>R y = norm y *\<^sub>R x"
2.363    (is "?lhs \<longleftrightarrow> ?rhs")
2.364 -proof -
2.365 -  {
2.366 -    assume h: "x = 0"
2.367 -    then have ?thesis by simp
2.368 -  }
2.369 -  moreover
2.370 -  {
2.371 -    assume h: "y = 0"
2.372 -    then have ?thesis by simp
2.373 -  }
2.374 -  moreover
2.375 -  {
2.376 -    assume x: "x \<noteq> 0" and y: "y \<noteq> 0"
2.377 -    from inner_eq_zero_iff[of "norm y *\<^sub>R x - norm x *\<^sub>R y"]
2.378 -    have "?rhs \<longleftrightarrow>
2.379 +proof (cases "x=0")
2.380 +  case True
2.381 +  then show ?thesis
2.382 +    by auto
2.383 +next
2.384 +  case False
2.385 +  from inner_eq_zero_iff[of "norm y *\<^sub>R x - norm x *\<^sub>R y"]
2.386 +  have "?rhs \<longleftrightarrow>
2.387        (norm y * (norm y * norm x * norm x - norm x * (x \<bullet> y)) -
2.388          norm x * (norm y * (y \<bullet> x) - norm x * norm y * norm y) =  0)"
2.389 -      using x y
2.390 -      unfolding inner_simps
2.391 -      unfolding power2_norm_eq_inner[symmetric] power2_eq_square right_minus_eq
2.392 -      apply (simp add: inner_commute)
2.393 -      apply (simp add: field_simps)
2.394 -      apply metis
2.395 -      done
2.396 -    also have "\<dots> \<longleftrightarrow> (2 * norm x * norm y * (norm x * norm y - x \<bullet> y) = 0)" using x y
2.397 -      by (simp add: field_simps inner_commute)
2.398 -    also have "\<dots> \<longleftrightarrow> ?lhs" using x y
2.399 -      apply simp
2.400 -      apply metis
2.401 -      done
2.402 -    finally have ?thesis by blast
2.403 -  }
2.404 -  ultimately show ?thesis by blast
2.405 +    using False unfolding inner_simps
2.406 +    by (auto simp add: power2_norm_eq_inner[symmetric] power2_eq_square inner_commute field_simps)
2.407 +  also have "\<dots> \<longleftrightarrow> (2 * norm x * norm y * (norm x * norm y - x \<bullet> y) = 0)"
2.408 +    using False  by (simp add: field_simps inner_commute)
2.409 +  also have "\<dots> \<longleftrightarrow> ?lhs"
2.410 +    using False by auto
2.411 +  finally show ?thesis by metis
2.412  qed
2.413
2.414  lemma norm_cauchy_schwarz_abs_eq:
2.415 @@ -3088,7 +3001,7 @@
2.416      by arith
2.417    have "?rhs \<longleftrightarrow> norm x *\<^sub>R y = norm y *\<^sub>R x \<or> norm (- x) *\<^sub>R y = norm y *\<^sub>R (- x)"
2.418      by simp
2.419 -  also have "\<dots> \<longleftrightarrow>(x \<bullet> y = norm x * norm y \<or> (- x) \<bullet> y = norm x * norm y)"
2.420 +  also have "\<dots> \<longleftrightarrow> (x \<bullet> y = norm x * norm y \<or> (- x) \<bullet> y = norm x * norm y)"
2.421      unfolding norm_cauchy_schwarz_eq[symmetric]
2.422      unfolding norm_minus_cancel norm_scaleR ..
2.423    also have "\<dots> \<longleftrightarrow> ?lhs"
2.424 @@ -3100,33 +3013,21 @@
2.425  lemma norm_triangle_eq:
2.426    fixes x y :: "'a::real_inner"
2.427    shows "norm (x + y) = norm x + norm y \<longleftrightarrow> norm x *\<^sub>R y = norm y *\<^sub>R x"
2.428 -proof -
2.429 -  {
2.430 -    assume x: "x = 0 \<or> y = 0"
2.431 -    then have ?thesis
2.432 -      by (cases "x = 0") simp_all
2.433 -  }
2.434 -  moreover
2.435 -  {
2.436 -    assume x: "x \<noteq> 0" and y: "y \<noteq> 0"
2.437 -    then have "norm x \<noteq> 0" "norm y \<noteq> 0"
2.438 -      by simp_all
2.439 -    then have n: "norm x > 0" "norm y > 0"
2.440 -      using norm_ge_zero[of x] norm_ge_zero[of y] by arith+
2.441 -    have th: "\<And>(a::real) b c. a + b + c \<noteq> 0 \<Longrightarrow> a = b + c \<longleftrightarrow> a\<^sup>2 = (b + c)\<^sup>2"
2.442 -      by algebra
2.443 -    have "norm (x + y) = norm x + norm y \<longleftrightarrow> (norm (x + y))\<^sup>2 = (norm x + norm y)\<^sup>2"
2.444 -      apply (rule th)
2.445 -      using n norm_ge_zero[of "x + y"]
2.446 -      apply arith
2.447 -      done
2.448 -    also have "\<dots> \<longleftrightarrow> norm x *\<^sub>R y = norm y *\<^sub>R x"
2.449 -      unfolding norm_cauchy_schwarz_eq[symmetric]
2.450 -      unfolding power2_norm_eq_inner inner_simps
2.451 -      by (simp add: power2_norm_eq_inner[symmetric] power2_eq_square inner_commute field_simps)
2.452 -    finally have ?thesis .
2.453 -  }
2.454 -  ultimately show ?thesis by blast
2.455 +proof (cases "x = 0 \<or> y = 0")
2.456 +  case True
2.457 +  then show ?thesis
2.458 +    by force
2.459 +next
2.460 +  case False
2.461 +  then have n: "norm x > 0" "norm y > 0"
2.462 +    by auto
2.463 +  have "norm (x + y) = norm x + norm y \<longleftrightarrow> (norm (x + y))\<^sup>2 = (norm x + norm y)\<^sup>2"
2.464 +    by simp
2.465 +  also have "\<dots> \<longleftrightarrow> norm x *\<^sub>R y = norm y *\<^sub>R x"
2.466 +    unfolding norm_cauchy_schwarz_eq[symmetric]
2.467 +    unfolding power2_norm_eq_inner inner_simps
2.468 +    by (simp add: power2_norm_eq_inner[symmetric] power2_eq_square inner_commute field_simps)
2.469 +  finally show ?thesis .
2.470  qed
2.471
2.472
2.473 @@ -3185,81 +3086,67 @@
2.474  lemma collinear_2 [iff]: "collinear {x, y}"
2.475    apply (simp add: collinear_def)
2.476    apply (rule exI[where x="x - y"])
2.477 -  apply auto
2.478 -  apply (rule exI[where x=1], simp)
2.479 -  apply (rule exI[where x="- 1"], simp)
2.480 -  done
2.481 +  by (metis minus_diff_eq scaleR_left.minus scaleR_one)
2.482
2.483  lemma collinear_lemma: "collinear {0, x, y} \<longleftrightarrow> x = 0 \<or> y = 0 \<or> (\<exists>c. y = c *\<^sub>R x)"
2.484    (is "?lhs \<longleftrightarrow> ?rhs")
2.485 -proof -
2.486 -  {
2.487 -    assume "x = 0 \<or> y = 0"
2.488 -    then have ?thesis
2.489 -      by (cases "x = 0") (simp_all add: collinear_2 insert_commute)
2.490 -  }
2.491 -  moreover
2.492 -  {
2.493 -    assume x: "x \<noteq> 0" and y: "y \<noteq> 0"
2.494 -    have ?thesis
2.495 -    proof
2.496 -      assume h: "?lhs"
2.497 -      then obtain u where u: "\<forall> x\<in> {0,x,y}. \<forall>y\<in> {0,x,y}. \<exists>c. x - y = c *\<^sub>R u"
2.498 -        unfolding collinear_def by blast
2.499 -      from u[rule_format, of x 0] u[rule_format, of y 0]
2.500 -      obtain cx and cy where
2.501 -        cx: "x = cx *\<^sub>R u" and cy: "y = cy *\<^sub>R u"
2.502 -        by auto
2.503 -      from cx x have cx0: "cx \<noteq> 0" by auto
2.504 -      from cy y have cy0: "cy \<noteq> 0" by auto
2.505 -      let ?d = "cy / cx"
2.506 -      from cx cy cx0 have "y = ?d *\<^sub>R x"
2.507 -        by simp
2.508 -      then show ?rhs using x y by blast
2.509 -    next
2.510 -      assume h: "?rhs"
2.511 -      then obtain c where c: "y = c *\<^sub>R x"
2.512 -        using x y by blast
2.513 -      show ?lhs
2.514 -        unfolding collinear_def c
2.515 -        apply (rule exI[where x=x])
2.516 -        apply auto
2.517 -        apply (rule exI[where x="- 1"], simp)
2.518 -        apply (rule exI[where x= "-c"], simp)
2.519 +proof (cases "x = 0 \<or> y = 0")
2.520 +  case True
2.521 +  then show ?thesis
2.522 +    by (auto simp: insert_commute)
2.523 +next
2.524 +  case False
2.525 +  show ?thesis
2.526 +  proof
2.527 +    assume h: "?lhs"
2.528 +    then obtain u where u: "\<forall> x\<in> {0,x,y}. \<forall>y\<in> {0,x,y}. \<exists>c. x - y = c *\<^sub>R u"
2.529 +      unfolding collinear_def by blast
2.530 +    from u[rule_format, of x 0] u[rule_format, of y 0]
2.531 +    obtain cx and cy where
2.532 +      cx: "x = cx *\<^sub>R u" and cy: "y = cy *\<^sub>R u"
2.533 +      by auto
2.534 +    from cx cy False have cx0: "cx \<noteq> 0" and cy0: "cy \<noteq> 0" by auto
2.535 +    let ?d = "cy / cx"
2.536 +    from cx cy cx0 have "y = ?d *\<^sub>R x"
2.537 +      by simp
2.538 +    then show ?rhs using False by blast
2.539 +  next
2.540 +    assume h: "?rhs"
2.541 +    then obtain c where c: "y = c *\<^sub>R x"
2.542 +      using False by blast
2.543 +    show ?lhs
2.544 +      unfolding collinear_def c
2.545 +      apply (rule exI[where x=x])
2.546 +      apply auto
2.547 +          apply (rule exI[where x="- 1"], simp)
2.548 +         apply (rule exI[where x= "-c"], simp)
2.549          apply (rule exI[where x=1], simp)
2.550 -        apply (rule exI[where x="1 - c"], simp add: scaleR_left_diff_distrib)
2.551 -        apply (rule exI[where x="c - 1"], simp add: scaleR_left_diff_distrib)
2.552 -        done
2.553 -    qed
2.554 -  }
2.555 -  ultimately show ?thesis by blast
2.556 +       apply (rule exI[where x="1 - c"], simp add: scaleR_left_diff_distrib)
2.557 +      apply (rule exI[where x="c - 1"], simp add: scaleR_left_diff_distrib)
2.558 +      done
2.559 +  qed
2.560  qed
2.561
2.562  lemma norm_cauchy_schwarz_equal: "\<bar>x \<bullet> y\<bar> = norm x * norm y \<longleftrightarrow> collinear {0, x, y}"
2.563 -  unfolding norm_cauchy_schwarz_abs_eq
2.564 -  apply (cases "x=0", simp_all)
2.565 -  apply (cases "y=0", simp_all add: insert_commute)
2.566 -  unfolding collinear_lemma
2.567 -  apply simp
2.568 -  apply (subgoal_tac "norm x \<noteq> 0")
2.569 -  apply (subgoal_tac "norm y \<noteq> 0")
2.570 -  apply (rule iffI)
2.571 -  apply (cases "norm x *\<^sub>R y = norm y *\<^sub>R x")
2.572 -  apply (rule exI[where x="(1/norm x) * norm y"])
2.573 -  apply (drule sym)
2.574 -  unfolding scaleR_scaleR[symmetric]
2.575 -  apply (simp add: field_simps)
2.576 -  apply (rule exI[where x="(1/norm x) * - norm y"])
2.577 -  apply clarify
2.578 -  apply (drule sym)
2.579 -  unfolding scaleR_scaleR[symmetric]
2.580 -  apply (simp add: field_simps)
2.581 -  apply (erule exE)
2.582 -  apply (erule ssubst)
2.583 -  unfolding scaleR_scaleR
2.584 -  unfolding norm_scaleR
2.585 -  apply (subgoal_tac "norm x * c = \<bar>c\<bar> * norm x \<or> norm x * c = - \<bar>c\<bar> * norm x")
2.586 -  apply (auto simp add: field_simps)
2.587 -  done
2.588 +proof (cases "x=0")
2.589 +  case True
2.590 +  then show ?thesis
2.591 +    by (auto simp: insert_commute)
2.592 +next
2.593 +  case False
2.594 +  then have nnz: "norm x \<noteq> 0"
2.595 +    by auto
2.596 +  show ?thesis
2.597 +  proof
2.598 +    assume "\<bar>x \<bullet> y\<bar> = norm x * norm y"
2.599 +    then show "collinear {0, x, y}"
2.600 +      unfolding norm_cauchy_schwarz_abs_eq collinear_lemma
2.601 +      by (meson eq_vector_fraction_iff nnz)
2.602 +  next
2.603 +    assume "collinear {0, x, y}"
2.604 +    with False show "\<bar>x \<bullet> y\<bar> = norm x * norm y"
2.605 +      unfolding norm_cauchy_schwarz_abs_eq collinear_lemma  by (auto simp: abs_if)
2.606 +  qed
2.607 +qed
2.608
2.609  end
```