author  wenzelm 
Fri, 28 Sep 2012 23:40:48 +0200  
changeset 49653  03bc7afe8814 
parent 48125  602dc0215954 
child 49654  366d8b41ca17 
permissions  rwrr 
41959  1 
(* Title: HOL/Multivariate_Analysis/Path_Connected.thy 
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Author: Robert Himmelmann, TU Muenchen 
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*) 

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header {* Continuous paths and pathconnected sets *} 

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theory Path_Connected 

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imports Convex_Euclidean_Space 
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begin 
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subsection {* Paths. *} 

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definition path :: "(real \<Rightarrow> 'a::topological_space) \<Rightarrow> bool" 
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where "path g \<longleftrightarrow> continuous_on {0 .. 1} g" 
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definition pathstart :: "(real \<Rightarrow> 'a::topological_space) \<Rightarrow> 'a" 
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where "pathstart g = g 0" 
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definition pathfinish :: "(real \<Rightarrow> 'a::topological_space) \<Rightarrow> 'a" 
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where "pathfinish g = g 1" 
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definition path_image :: "(real \<Rightarrow> 'a::topological_space) \<Rightarrow> 'a set" 
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where "path_image g = g ` {0 .. 1}" 
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definition reversepath :: "(real \<Rightarrow> 'a::topological_space) \<Rightarrow> (real \<Rightarrow> 'a)" 
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where "reversepath g = (\<lambda>x. g(1  x))" 
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definition joinpaths :: "(real \<Rightarrow> 'a::topological_space) \<Rightarrow> (real \<Rightarrow> 'a) \<Rightarrow> (real \<Rightarrow> 'a)" 
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(infixr "+++" 75) 
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where "g1 +++ g2 = (\<lambda>x. if x \<le> 1/2 then g1 (2 * x) else g2 (2 * x  1))" 

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definition simple_path :: "(real \<Rightarrow> 'a::topological_space) \<Rightarrow> bool" 
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where "simple_path g \<longleftrightarrow> 
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(\<forall>x\<in>{0..1}. \<forall>y\<in>{0..1}. g x = g y \<longrightarrow> x = y \<or> x = 0 \<and> y = 1 \<or> x = 1 \<and> y = 0)" 
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definition injective_path :: "(real \<Rightarrow> 'a::topological_space) \<Rightarrow> bool" 
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where "injective_path g \<longleftrightarrow> (\<forall>x\<in>{0..1}. \<forall>y\<in>{0..1}. g x = g y \<longrightarrow> x = y)" 
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subsection {* Some lemmas about these concepts. *} 
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lemma injective_imp_simple_path: "injective_path g \<Longrightarrow> simple_path g" 
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unfolding injective_path_def simple_path_def by auto 
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lemma path_image_nonempty: "path_image g \<noteq> {}" 

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unfolding path_image_def image_is_empty interval_eq_empty by auto 

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lemma pathstart_in_path_image[intro]: "(pathstart g) \<in> path_image g" 

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unfolding pathstart_def path_image_def by auto 

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lemma pathfinish_in_path_image[intro]: "(pathfinish g) \<in> path_image g" 

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unfolding pathfinish_def path_image_def by auto 

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lemma connected_path_image[intro]: "path g \<Longrightarrow> connected(path_image g)" 

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unfolding path_def path_image_def 

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apply (erule connected_continuous_image) 

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apply (rule convex_connected, rule convex_real_interval) 
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done 

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lemma compact_path_image[intro]: "path g \<Longrightarrow> compact(path_image g)" 

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unfolding path_def path_image_def 

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by (erule compact_continuous_image, rule compact_interval) 
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lemma reversepath_reversepath[simp]: "reversepath(reversepath g) = g" 

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unfolding reversepath_def by auto 

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lemma pathstart_reversepath[simp]: "pathstart(reversepath g) = pathfinish g" 

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unfolding pathstart_def reversepath_def pathfinish_def by auto 

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lemma pathfinish_reversepath[simp]: "pathfinish(reversepath g) = pathstart g" 

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unfolding pathstart_def reversepath_def pathfinish_def by auto 

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lemma pathstart_join[simp]: "pathstart (g1 +++ g2) = pathstart g1" 
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unfolding pathstart_def joinpaths_def pathfinish_def by auto 
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lemma pathfinish_join[simp]: "pathfinish (g1 +++ g2) = pathfinish g2" 
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unfolding pathstart_def joinpaths_def pathfinish_def by auto 
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lemma path_image_reversepath[simp]: "path_image(reversepath g) = path_image g" 
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proof  

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have *: "\<And>g. path_image(reversepath g) \<subseteq> path_image g" 

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unfolding path_image_def subset_eq reversepath_def Ball_def image_iff 

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apply(rule,rule,erule bexE) 

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apply(rule_tac x="1  xa" in bexI) 

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apply auto 

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done 

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show ?thesis 

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using *[of g] *[of "reversepath g"] 

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unfolding reversepath_reversepath by auto 

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qed 

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lemma path_reversepath[simp]: "path (reversepath g) \<longleftrightarrow> path g" 
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proof  

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have *: "\<And>g. path g \<Longrightarrow> path (reversepath g)" 

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unfolding path_def reversepath_def 

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apply (rule continuous_on_compose[unfolded o_def, of _ "\<lambda>x. 1  x"]) 

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apply (intro continuous_on_intros) 

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apply (rule continuous_on_subset[of "{0..1}"], assumption) 

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apply auto 

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done 

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show ?thesis 

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using *[of "reversepath g"] *[of g] 

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unfolding reversepath_reversepath 

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by (rule iffI) 

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qed 

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lemmas reversepath_simps = 

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path_reversepath path_image_reversepath pathstart_reversepath pathfinish_reversepath 

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lemma path_join[simp]: 
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assumes "pathfinish g1 = pathstart g2" 

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shows "path (g1 +++ g2) \<longleftrightarrow> path g1 \<and> path g2" 

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unfolding path_def pathfinish_def pathstart_def 

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apply rule defer 

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apply(erule conjE) 

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proof  

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assume as: "continuous_on {0..1} (g1 +++ g2)" 

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have *: "g1 = (\<lambda>x. g1 (2 *\<^sub>R x)) \<circ> (\<lambda>x. (1/2) *\<^sub>R x)" 

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"g2 = (\<lambda>x. g2 (2 *\<^sub>R x  1)) \<circ> (\<lambda>x. (1/2) *\<^sub>R (x + 1))" 

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unfolding o_def by (auto simp add: add_divide_distrib) 
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have "op *\<^sub>R (1 / 2) ` {0::real..1} \<subseteq> {0..1}" 
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"(\<lambda>x. (1 / 2) *\<^sub>R (x + 1)) ` {(0::real)..1} \<subseteq> {0..1}" 

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by auto 
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then show "continuous_on {0..1} g1 \<and> continuous_on {0..1} g2" 
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apply  

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apply rule 

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apply (subst *) defer 

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apply (subst *) 

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apply (rule_tac[!] continuous_on_compose) 

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apply (intro continuous_on_intros) defer 
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apply (intro continuous_on_intros) 
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apply (rule_tac[!] continuous_on_eq[of _ "g1 +++ g2"]) defer prefer 3 
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apply (rule_tac[12] continuous_on_subset[of "{0 .. 1}"]) 

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apply (rule as, assumption, rule as, assumption) 

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apply rule defer 

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apply rule 

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proof  

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fix x 

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assume "x \<in> op *\<^sub>R (1 / 2) ` {0::real..1}" 

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hence "x \<le> 1 / 2" unfolding image_iff by auto 
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thus "(g1 +++ g2) x = g1 (2 *\<^sub>R x)" unfolding joinpaths_def by auto 
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next 

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fix x 

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assume "x \<in> (\<lambda>x. (1 / 2) *\<^sub>R (x + 1)) ` {0::real..1}" 

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hence "x \<ge> 1 / 2" unfolding image_iff by auto 
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thus "(g1 +++ g2) x = g2 (2 *\<^sub>R x  1)" 
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proof (cases "x = 1 / 2") 

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case True 

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hence "x = (1/2) *\<^sub>R 1" by auto 

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thus ?thesis 

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unfolding joinpaths_def 

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using assms[unfolded pathstart_def pathfinish_def] 

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by (auto simp add: mult_ac) 

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qed (auto simp add:le_less joinpaths_def) 

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qed 

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next 

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assume as:"continuous_on {0..1} g1" "continuous_on {0..1} g2" 

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have *: "{0 .. 1::real} = {0.. (1/2)*\<^sub>R 1} \<union> {(1/2) *\<^sub>R 1 .. 1}" by auto 

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have **: "op *\<^sub>R 2 ` {0..(1 / 2) *\<^sub>R 1} = {0..1::real}" 

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apply (rule set_eqI, rule) 

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unfolding image_iff 

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defer 

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apply (rule_tac x="(1/2)*\<^sub>R x" in bexI) 

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apply auto 

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done 

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have ***: "(\<lambda>x. 2 *\<^sub>R x  1) ` {(1 / 2) *\<^sub>R 1..1} = {0..1::real}" 

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apply (auto simp add: image_def) 
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apply (rule_tac x="(x + 1) / 2" in bexI) 

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apply (auto simp add: add_divide_distrib) 

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done 

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show "continuous_on {0..1} (g1 +++ g2)" 
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unfolding * 

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apply (rule continuous_on_union) 

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apply (rule closed_real_atLeastAtMost)+ 

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proof  

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show "continuous_on {0..(1 / 2) *\<^sub>R 1} (g1 +++ g2)" 

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apply (rule continuous_on_eq[of _ "\<lambda>x. g1 (2 *\<^sub>R x)"]) defer 

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unfolding o_def[THEN sym] 

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apply (rule continuous_on_compose) 

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apply (intro continuous_on_intros) 

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unfolding ** 

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apply (rule as(1)) 

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unfolding joinpaths_def 

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apply auto 

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done 

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next 

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show "continuous_on {(1/2)*\<^sub>R1..1} (g1 +++ g2)" 

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apply (rule continuous_on_eq[of _ "g2 \<circ> (\<lambda>x. 2 *\<^sub>R x  1)"]) defer 

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apply (rule continuous_on_compose) 

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apply (intro continuous_on_intros) 

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unfolding *** o_def joinpaths_def 

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apply (rule as(2)) 

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using assms[unfolded pathstart_def pathfinish_def] 

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apply (auto simp add: mult_ac) 

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done 

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qed 

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qed 

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lemma path_image_join_subset: "path_image(g1 +++ g2) \<subseteq> (path_image g1 \<union> path_image g2)" 
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proof 

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fix x 

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assume "x \<in> path_image (g1 +++ g2)" 

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then obtain y where y:"y\<in>{0..1}" "x = (if y \<le> 1 / 2 then g1 (2 *\<^sub>R y) else g2 (2 *\<^sub>R y  1))" 
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unfolding path_image_def image_iff joinpaths_def by auto 

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thus "x \<in> path_image g1 \<union> path_image g2" 
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apply (cases "y \<le> 1/2") 

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apply (rule_tac UnI1) defer 

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apply (rule_tac UnI2) 

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unfolding y(2) path_image_def 

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using y(1) 

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apply (auto intro!: imageI) 

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done 

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qed 

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lemma subset_path_image_join: 

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assumes "path_image g1 \<subseteq> s" "path_image g2 \<subseteq> s" 
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shows "path_image(g1 +++ g2) \<subseteq> s" 

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using path_image_join_subset[of g1 g2] and assms by auto 
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lemma path_image_join: 

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assumes "path g1" "path g2" "pathfinish g1 = pathstart g2" 

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shows "path_image(g1 +++ g2) = (path_image g1) \<union> (path_image g2)" 

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apply (rule, rule path_image_join_subset, rule) 
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unfolding Un_iff 

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proof (erule disjE) 

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fix x 

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assume "x \<in> path_image g1" 

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then obtain y where y: "y\<in>{0..1}" "x = g1 y" 

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unfolding path_image_def image_iff by auto 

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thus "x \<in> path_image (g1 +++ g2)" 

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unfolding joinpaths_def path_image_def image_iff 

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apply (rule_tac x="(1/2) *\<^sub>R y" in bexI) 

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apply auto 

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done 

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next 

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fix x 

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assume "x \<in> path_image g2" 

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then obtain y where y: "y\<in>{0..1}" "x = g2 y" 

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unfolding path_image_def image_iff by auto 

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then show "x \<in> path_image (g1 +++ g2)" 

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unfolding joinpaths_def path_image_def image_iff 

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apply(rule_tac x="(1/2) *\<^sub>R (y + 1)" in bexI) 

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using assms(3)[unfolded pathfinish_def pathstart_def] 

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apply (auto simp add: add_divide_distrib) 

245 
done 

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qed 

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lemma not_in_path_image_join: 

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assumes "x \<notin> path_image g1" "x \<notin> path_image g2" 
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shows "x \<notin> path_image(g1 +++ g2)" 

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using assms and path_image_join_subset[of g1 g2] by auto 
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49653  253 
lemma simple_path_reversepath: 
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assumes "simple_path g" 

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shows "simple_path (reversepath g)" 

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using assms 

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unfolding simple_path_def reversepath_def 

258 
apply  

259 
apply (rule ballI)+ 

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apply (erule_tac x="1x" in ballE, erule_tac x="1y" in ballE) 

261 
apply auto 

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done 

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lemma simple_path_join_loop: 

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assumes "injective_path g1" "injective_path g2" "pathfinish g2 = pathstart g1" 

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"(path_image g1 \<inter> path_image g2) \<subseteq> {pathstart g1,pathstart g2}" 
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shows "simple_path(g1 +++ g2)" 
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unfolding simple_path_def 
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proof ((rule ballI)+, rule impI) 

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let ?g = "g1 +++ g2" 

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note inj = assms(1,2)[unfolded injective_path_def, rule_format] 
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fix x y :: real 
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assume xy: "x \<in> {0..1}" "y \<in> {0..1}" "?g x = ?g y" 

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show "x = y \<or> x = 0 \<and> y = 1 \<or> x = 1 \<and> y = 0" 

275 
proof (case_tac "x \<le> 1/2", case_tac[!] "y \<le> 1/2", unfold not_le) 

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assume as: "x \<le> 1 / 2" "y \<le> 1 / 2" 

277 
hence "g1 (2 *\<^sub>R x) = g1 (2 *\<^sub>R y)" 

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using xy(3) unfolding joinpaths_def by auto 

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moreover 

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have "2 *\<^sub>R x \<in> {0..1}" "2 *\<^sub>R y \<in> {0..1}" using xy(1,2) as 

36583  281 
by auto 
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ultimately 
283 
show ?thesis using inj(1)[of "2*\<^sub>R x" "2*\<^sub>R y"] by auto 

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next 

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assume as:"x > 1 / 2" "y > 1 / 2" 

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hence "g2 (2 *\<^sub>R x  1) = g2 (2 *\<^sub>R y  1)" 

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using xy(3) unfolding joinpaths_def by auto 

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moreover 

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have "2 *\<^sub>R x  1 \<in> {0..1}" "2 *\<^sub>R y  1 \<in> {0..1}" 

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using xy(1,2) as by auto 

291 
ultimately 

292 
show ?thesis using inj(2)[of "2*\<^sub>R x  1" "2*\<^sub>R y  1"] by auto 

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next 

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assume as:"x \<le> 1 / 2" "y > 1 / 2" 

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hence "?g x \<in> path_image g1" "?g y \<in> path_image g2" 

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unfolding path_image_def joinpaths_def 

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using xy(1,2) by auto 
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moreover 
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have "?g y \<noteq> pathstart g2" using as(2) unfolding pathstart_def joinpaths_def 

36583  300 
using inj(2)[of "2 *\<^sub>R y  1" 0] and xy(2) 
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by (auto simp add: field_simps) 

49653  302 
ultimately 
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have *:"?g x = pathstart g1" using assms(4) unfolding xy(3) by auto 

36583  304 
hence "x = 0" unfolding pathstart_def joinpaths_def using as(1) and xy(1) 
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using inj(1)[of "2 *\<^sub>R x" 0] by auto 

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moreover 
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have "y = 1" using * unfolding xy(3) assms(3)[THEN sym] 

36583  308 
unfolding joinpaths_def pathfinish_def using as(2) and xy(2) 
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using inj(2)[of "2 *\<^sub>R y  1" 1] by auto 

310 
ultimately show ?thesis by auto 

49653  311 
next 
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assume as: "x > 1 / 2" "y \<le> 1 / 2" 

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hence "?g x \<in> path_image g2" "?g y \<in> path_image g1" 

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unfolding path_image_def joinpaths_def 

36583  315 
using xy(1,2) by auto 
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moreover 
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have "?g x \<noteq> pathstart g2" using as(1) unfolding pathstart_def joinpaths_def 

36583  318 
using inj(2)[of "2 *\<^sub>R x  1" 0] and xy(1) 
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by (auto simp add: field_simps) 

49653  320 
ultimately 
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have *: "?g y = pathstart g1" using assms(4) unfolding xy(3) by auto 

36583  322 
hence "y = 0" unfolding pathstart_def joinpaths_def using as(2) and xy(2) 
323 
using inj(1)[of "2 *\<^sub>R y" 0] by auto 

49653  324 
moreover 
325 
have "x = 1" using * unfolding xy(3)[THEN sym] assms(3)[THEN sym] 

36583  326 
unfolding joinpaths_def pathfinish_def using as(1) and xy(1) 
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using inj(2)[of "2 *\<^sub>R x  1" 1] by auto 

49653  328 
ultimately show ?thesis by auto 
329 
qed 

330 
qed 

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lemma injective_path_join: 

333 
assumes "injective_path g1" "injective_path g2" "pathfinish g1 = pathstart g2" 

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"(path_image g1 \<inter> path_image g2) \<subseteq> {pathstart g2}" 
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shows "injective_path(g1 +++ g2)" 
49653  336 
unfolding injective_path_def 
337 
proof (rule, rule, rule) 

338 
let ?g = "g1 +++ g2" 

36583  339 
note inj = assms(1,2)[unfolded injective_path_def, rule_format] 
49653  340 
fix x y 
341 
assume xy: "x \<in> {0..1}" "y \<in> {0..1}" "(g1 +++ g2) x = (g1 +++ g2) y" 

342 
show "x = y" 

343 
proof (cases "x \<le> 1/2", case_tac[!] "y \<le> 1/2", unfold not_le) 

344 
assume "x \<le> 1 / 2" "y \<le> 1 / 2" 

345 
thus ?thesis using inj(1)[of "2*\<^sub>R x" "2*\<^sub>R y"] and xy 

36583  346 
unfolding joinpaths_def by auto 
49653  347 
next 
348 
assume "x > 1 / 2" "y > 1 / 2" 

349 
thus ?thesis using inj(2)[of "2*\<^sub>R x  1" "2*\<^sub>R y  1"] and xy 

36583  350 
unfolding joinpaths_def by auto 
49653  351 
next 
352 
assume as: "x \<le> 1 / 2" "y > 1 / 2" 

353 
hence "?g x \<in> path_image g1" "?g y \<in> path_image g2" 

354 
unfolding path_image_def joinpaths_def 

36583  355 
using xy(1,2) by auto 
49653  356 
hence "?g x = pathfinish g1" "?g y = pathstart g2" 
357 
using assms(4) unfolding assms(3) xy(3) by auto 

358 
thus ?thesis 

359 
using as and inj(1)[of "2 *\<^sub>R x" 1] inj(2)[of "2 *\<^sub>R y  1" 0] and xy(1,2) 

36583  360 
unfolding pathstart_def pathfinish_def joinpaths_def 
361 
by auto 

49653  362 
next 
363 
assume as:"x > 1 / 2" "y \<le> 1 / 2" 

364 
hence "?g x \<in> path_image g2" "?g y \<in> path_image g1" 

365 
unfolding path_image_def joinpaths_def 

36583  366 
using xy(1,2) by auto 
49653  367 
hence "?g x = pathstart g2" "?g y = pathfinish g1" 
368 
using assms(4) unfolding assms(3) xy(3) by auto 

36583  369 
thus ?thesis using as and inj(2)[of "2 *\<^sub>R x  1" 0] inj(1)[of "2 *\<^sub>R y" 1] and xy(1,2) 
370 
unfolding pathstart_def pathfinish_def joinpaths_def 

49653  371 
by auto 
372 
qed 

373 
qed 

36583  374 

375 
lemmas join_paths_simps = path_join path_image_join pathstart_join pathfinish_join 

376 

49653  377 

36583  378 
subsection {* Reparametrizing a closed curve to start at some chosen point. *} 
379 

380 
definition "shiftpath a (f::real \<Rightarrow> 'a::topological_space) = 

381 
(\<lambda>x. if (a + x) \<le> 1 then f(a + x) else f(a + x  1))" 

382 

383 
lemma pathstart_shiftpath: "a \<le> 1 \<Longrightarrow> pathstart(shiftpath a g) = g a" 

384 
unfolding pathstart_def shiftpath_def by auto 

385 

49653  386 
lemma pathfinish_shiftpath: 
387 
assumes "0 \<le> a" "pathfinish g = pathstart g" 

36583  388 
shows "pathfinish(shiftpath a g) = g a" 
389 
using assms unfolding pathstart_def pathfinish_def shiftpath_def 

390 
by auto 

391 

392 
lemma endpoints_shiftpath: 

393 
assumes "pathfinish g = pathstart g" "a \<in> {0 .. 1}" 

394 
shows "pathfinish(shiftpath a g) = g a" "pathstart(shiftpath a g) = g a" 

395 
using assms by(auto intro!:pathfinish_shiftpath pathstart_shiftpath) 

396 

397 
lemma closed_shiftpath: 

398 
assumes "pathfinish g = pathstart g" "a \<in> {0..1}" 

399 
shows "pathfinish(shiftpath a g) = pathstart(shiftpath a g)" 

400 
using endpoints_shiftpath[OF assms] by auto 

401 

402 
lemma path_shiftpath: 

403 
assumes "path g" "pathfinish g = pathstart g" "a \<in> {0..1}" 

49653  404 
shows "path(shiftpath a g)" 
405 
proof  

406 
have *: "{0 .. 1} = {0 .. 1a} \<union> {1a .. 1}" using assms(3) by auto 

407 
have **: "\<And>x. x + a = 1 \<Longrightarrow> g (x + a  1) = g (x + a)" 

36583  408 
using assms(2)[unfolded pathfinish_def pathstart_def] by auto 
49653  409 
show ?thesis 
410 
unfolding path_def shiftpath_def * 

411 
apply (rule continuous_on_union) 

412 
apply (rule closed_real_atLeastAtMost)+ 

413 
apply (rule continuous_on_eq[of _ "g \<circ> (\<lambda>x. a + x)"]) prefer 3 

414 
apply (rule continuous_on_eq[of _ "g \<circ> (\<lambda>x. a  1 + x)"]) defer prefer 3 

415 
apply (rule continuous_on_intros)+ prefer 2 

416 
apply (rule continuous_on_intros)+ 

417 
apply (rule_tac[12] continuous_on_subset[OF assms(1)[unfolded path_def]]) 

418 
using assms(3) and ** 

419 
apply (auto, auto simp add: field_simps) 

420 
done 

421 
qed 

36583  422 

49653  423 
lemma shiftpath_shiftpath: 
424 
assumes "pathfinish g = pathstart g" "a \<in> {0..1}" "x \<in> {0..1}" 

36583  425 
shows "shiftpath (1  a) (shiftpath a g) x = g x" 
426 
using assms unfolding pathfinish_def pathstart_def shiftpath_def by auto 

427 

428 
lemma path_image_shiftpath: 

429 
assumes "a \<in> {0..1}" "pathfinish g = pathstart g" 

49653  430 
shows "path_image(shiftpath a g) = path_image g" 
431 
proof  

432 
{ fix x 

433 
assume as:"g 1 = g 0" "x \<in> {0..1::real}" " \<forall>y\<in>{0..1} \<inter> {x. \<not> a + x \<le> 1}. g x \<noteq> g (a + y  1)" 

434 
hence "\<exists>y\<in>{0..1} \<inter> {x. a + x \<le> 1}. g x = g (a + y)" 

435 
proof (cases "a \<le> x") 

436 
case False 

437 
thus ?thesis 

438 
apply (rule_tac x="1 + x  a" in bexI) 

36583  439 
using as(1,2) and as(3)[THEN bspec[where x="1 + x  a"]] and assms(1) 
49653  440 
apply (auto simp add: field_simps atomize_not) 
441 
done 

442 
next 

443 
case True 

444 
thus ?thesis using as(12) and assms(1) apply(rule_tac x="x  a" in bexI) 

445 
by(auto simp add: field_simps) 

446 
qed 

447 
} 

448 
thus ?thesis 

449 
using assms unfolding shiftpath_def path_image_def pathfinish_def pathstart_def 

450 
by(auto simp add: image_iff) 

451 
qed 

452 

36583  453 

454 
subsection {* Special case of straightline paths. *} 

455 

49653  456 
definition linepath :: "'a::real_normed_vector \<Rightarrow> 'a \<Rightarrow> real \<Rightarrow> 'a" 
457 
where "linepath a b = (\<lambda>x. (1  x) *\<^sub>R a + x *\<^sub>R b)" 

36583  458 

459 
lemma pathstart_linepath[simp]: "pathstart(linepath a b) = a" 

460 
unfolding pathstart_def linepath_def by auto 

461 

462 
lemma pathfinish_linepath[simp]: "pathfinish(linepath a b) = b" 

463 
unfolding pathfinish_def linepath_def by auto 

464 

465 
lemma continuous_linepath_at[intro]: "continuous (at x) (linepath a b)" 

466 
unfolding linepath_def by (intro continuous_intros) 

467 

468 
lemma continuous_on_linepath[intro]: "continuous_on s (linepath a b)" 

469 
using continuous_linepath_at by(auto intro!: continuous_at_imp_continuous_on) 

470 

471 
lemma path_linepath[intro]: "path(linepath a b)" 

472 
unfolding path_def by(rule continuous_on_linepath) 

473 

474 
lemma path_image_linepath[simp]: "path_image(linepath a b) = (closed_segment a b)" 

49653  475 
unfolding path_image_def segment linepath_def 
476 
apply (rule set_eqI, rule) defer 

477 
unfolding mem_Collect_eq image_iff 

478 
apply(erule exE) 

479 
apply(rule_tac x="u *\<^sub>R 1" in bexI) 

480 
apply auto 

481 
done 

482 

483 
lemma reversepath_linepath[simp]: "reversepath(linepath a b) = linepath b a" 

484 
unfolding reversepath_def linepath_def 

36583  485 
by auto 
486 

487 
lemma injective_path_linepath: 

49653  488 
assumes "a \<noteq> b" 
489 
shows "injective_path (linepath a b)" 

36583  490 
proof  
491 
{ fix x y :: "real" 

492 
assume "x *\<^sub>R b + y *\<^sub>R a = x *\<^sub>R a + y *\<^sub>R b" 

493 
hence "(x  y) *\<^sub>R a = (x  y) *\<^sub>R b" by (simp add: algebra_simps) 

494 
with assms have "x = y" by simp } 

49653  495 
thus ?thesis 
496 
unfolding injective_path_def linepath_def 

497 
by (auto simp add: algebra_simps) 

498 
qed 

36583  499 

49653  500 
lemma simple_path_linepath[intro]: "a \<noteq> b \<Longrightarrow> simple_path(linepath a b)" 
501 
by(auto intro!: injective_imp_simple_path injective_path_linepath) 

502 

36583  503 

504 
subsection {* Bounding a point away from a path. *} 

505 

506 
lemma not_on_path_ball: 

507 
fixes g :: "real \<Rightarrow> 'a::heine_borel" 

508 
assumes "path g" "z \<notin> path_image g" 

49653  509 
shows "\<exists>e > 0. ball z e \<inter> (path_image g) = {}" 
510 
proof  

511 
obtain a where "a \<in> path_image g" "\<forall>y \<in> path_image g. dist z a \<le> dist z y" 

36583  512 
using distance_attains_inf[OF _ path_image_nonempty, of g z] 
513 
using compact_path_image[THEN compact_imp_closed, OF assms(1)] by auto 

49653  514 
thus ?thesis 
515 
apply (rule_tac x="dist z a" in exI) 

516 
using assms(2) 

517 
apply (auto intro!: dist_pos_lt) 

518 
done 

519 
qed 

36583  520 

521 
lemma not_on_path_cball: 

522 
fixes g :: "real \<Rightarrow> 'a::heine_borel" 

523 
assumes "path g" "z \<notin> path_image g" 

49653  524 
shows "\<exists>e>0. cball z e \<inter> (path_image g) = {}" 
525 
proof  

526 
obtain e where "ball z e \<inter> path_image g = {}" "e>0" 

527 
using not_on_path_ball[OF assms] by auto 

36583  528 
moreover have "cball z (e/2) \<subseteq> ball z e" using `e>0` by auto 
49653  529 
ultimately show ?thesis apply(rule_tac x="e/2" in exI) by auto 
530 
qed 

531 

36583  532 

533 
subsection {* Path component, considered as a "joinability" relation (from Tom Hales). *} 

534 

49653  535 
definition "path_component s x y \<longleftrightarrow> 
536 
(\<exists>g. path g \<and> path_image g \<subseteq> s \<and> pathstart g = x \<and> pathfinish g = y)" 

36583  537 

538 
lemmas path_defs = path_def pathstart_def pathfinish_def path_image_def path_component_def 

539 

49653  540 
lemma path_component_mem: 
541 
assumes "path_component s x y" 

542 
shows "x \<in> s" "y \<in> s" 

36583  543 
using assms unfolding path_defs by auto 
544 

49653  545 
lemma path_component_refl: 
546 
assumes "x \<in> s" 

547 
shows "path_component s x x" 

548 
unfolding path_defs 

549 
apply (rule_tac x="\<lambda>u. x" in exI) 

550 
using assms apply (auto intro!:continuous_on_intros) done 

36583  551 

552 
lemma path_component_refl_eq: "path_component s x x \<longleftrightarrow> x \<in> s" 

49653  553 
by (auto intro!: path_component_mem path_component_refl) 
36583  554 

555 
lemma path_component_sym: "path_component s x y \<Longrightarrow> path_component s y x" 

49653  556 
using assms 
557 
unfolding path_component_def 

558 
apply (erule exE) 

559 
apply (rule_tac x="reversepath g" in exI) 

560 
apply auto 

561 
done 

36583  562 

49653  563 
lemma path_component_trans: 
564 
assumes "path_component s x y" "path_component s y z" 

565 
shows "path_component s x z" 

566 
using assms 

567 
unfolding path_component_def 

568 
apply  

569 
apply (erule exE)+ 

570 
apply (rule_tac x="g +++ ga" in exI) 

571 
apply (auto simp add: path_image_join) 

572 
done 

36583  573 

574 
lemma path_component_of_subset: "s \<subseteq> t \<Longrightarrow> path_component s x y \<Longrightarrow> path_component t x y" 

575 
unfolding path_component_def by auto 

576 

49653  577 

36583  578 
subsection {* Can also consider it as a set, as the name suggests. *} 
579 

49653  580 
lemma path_component_set: 
581 
"{y. path_component s x y} = 

582 
{y. (\<exists>g. path g \<and> path_image g \<subseteq> s \<and> pathstart g = x \<and> pathfinish g = y)}" 

583 
apply (rule set_eqI) 

584 
unfolding mem_Collect_eq 

585 
unfolding path_component_def 

586 
apply auto 

587 
done 

36583  588 

44170
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41959
diff
changeset

589 
lemma path_component_subset: "{y. path_component s x y} \<subseteq> s" 
49653  590 
apply (rule, rule path_component_mem(2)) 
591 
apply auto 

592 
done 

36583  593 

44170
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make Multivariate_Analysis work with separate set type
huffman
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diff
changeset

594 
lemma path_component_eq_empty: "{y. path_component s x y} = {} \<longleftrightarrow> x \<notin> s" 
49653  595 
apply rule 
596 
apply (drule equals0D[of _ x]) defer 

597 
apply (rule equals0I) 

598 
unfolding mem_Collect_eq 

599 
apply (drule path_component_mem(1)) 

600 
using path_component_refl 

601 
apply auto 

602 
done 

603 

36583  604 

605 
subsection {* Path connectedness of a space. *} 

606 

49653  607 
definition "path_connected s \<longleftrightarrow> 
608 
(\<forall>x\<in>s. \<forall>y\<in>s. \<exists>g. path g \<and> (path_image g) \<subseteq> s \<and> pathstart g = x \<and> pathfinish g = y)" 

36583  609 

610 
lemma path_connected_component: "path_connected s \<longleftrightarrow> (\<forall>x\<in>s. \<forall>y\<in>s. path_component s x y)" 

611 
unfolding path_connected_def path_component_def by auto 

612 

44170
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41959
diff
changeset

613 
lemma path_connected_component_set: "path_connected s \<longleftrightarrow> (\<forall>x\<in>s. {y. path_component s x y} = s)" 
49653  614 
unfolding path_connected_component 
615 
apply (rule, rule, rule, rule path_component_subset) 

616 
unfolding subset_eq mem_Collect_eq Ball_def 

617 
apply auto 

618 
done 

619 

36583  620 

621 
subsection {* Some useful lemmas about pathconnectedness. *} 

622 

623 
lemma convex_imp_path_connected: 

624 
fixes s :: "'a::real_normed_vector set" 

625 
assumes "convex s" shows "path_connected s" 

49653  626 
unfolding path_connected_def 
627 
apply (rule, rule, rule_tac x = "linepath x y" in exI) 

628 
unfolding path_image_linepath 

629 
using assms [unfolded convex_contains_segment] 

630 
apply auto 

631 
done 

36583  632 

49653  633 
lemma path_connected_imp_connected: 
634 
assumes "path_connected s" 

635 
shows "connected s" 

636 
unfolding connected_def not_ex 

637 
apply (rule, rule, rule ccontr) 

638 
unfolding not_not 

639 
apply (erule conjE)+ 

640 
proof  

641 
fix e1 e2 

642 
assume as: "open e1" "open e2" "s \<subseteq> e1 \<union> e2" "e1 \<inter> e2 \<inter> s = {}" "e1 \<inter> s \<noteq> {}" "e2 \<inter> s \<noteq> {}" 

36583  643 
then obtain x1 x2 where obt:"x1\<in>e1\<inter>s" "x2\<in>e2\<inter>s" by auto 
644 
then obtain g where g:"path g" "path_image g \<subseteq> s" "pathstart g = x1" "pathfinish g = x2" 

645 
using assms[unfolded path_connected_def,rule_format,of x1 x2] by auto 

49653  646 
have *: "connected {0..1::real}" 
647 
by (auto intro!: convex_connected convex_real_interval) 

648 
have "{0..1} \<subseteq> {x \<in> {0..1}. g x \<in> e1} \<union> {x \<in> {0..1}. g x \<in> e2}" 

649 
using as(3) g(2)[unfolded path_defs] by blast 

650 
moreover have "{x \<in> {0..1}. g x \<in> e1} \<inter> {x \<in> {0..1}. g x \<in> e2} = {}" 

651 
using as(4) g(2)[unfolded path_defs] unfolding subset_eq by auto 

652 
moreover have "{x \<in> {0..1}. g x \<in> e1} \<noteq> {} \<and> {x \<in> {0..1}. g x \<in> e2} \<noteq> {}" 

653 
using g(3,4)[unfolded path_defs] using obt 

36583  654 
by (simp add: ex_in_conv [symmetric], metis zero_le_one order_refl) 
49653  655 
ultimately show False 
656 
using *[unfolded connected_local not_ex, rule_format, of "{x\<in>{0..1}. g x \<in> e1}" "{x\<in>{0..1}. g x \<in> e2}"] 

36583  657 
using continuous_open_in_preimage[OF g(1)[unfolded path_def] as(1)] 
49653  658 
using continuous_open_in_preimage[OF g(1)[unfolded path_def] as(2)] 
659 
by auto 

660 
qed 

36583  661 

662 
lemma open_path_component: 

663 
fixes s :: "'a::real_normed_vector set" (*TODO: generalize to metric_space*) 

49653  664 
assumes "open s" 
665 
shows "open {y. path_component s x y}" 

666 
unfolding open_contains_ball 

667 
proof 

668 
fix y 

669 
assume as: "y \<in> {y. path_component s x y}" 

670 
hence "y \<in> s" 

671 
apply  

672 
apply (rule path_component_mem(2)) 

673 
unfolding mem_Collect_eq 

674 
apply auto 

675 
done 

676 
then obtain e where e:"e>0" "ball y e \<subseteq> s" 

677 
using assms[unfolded open_contains_ball] by auto 

678 
show "\<exists>e > 0. ball y e \<subseteq> {y. path_component s x y}" 

679 
apply (rule_tac x=e in exI) 

680 
apply (rule,rule `e>0`, rule) 

681 
unfolding mem_ball mem_Collect_eq 

682 
proof  

683 
fix z 

684 
assume "dist y z < e" 

685 
thus "path_component s x z" 

686 
apply (rule_tac path_component_trans[of _ _ y]) defer 

687 
apply (rule path_component_of_subset[OF e(2)]) 

688 
apply (rule convex_imp_path_connected[OF convex_ball, unfolded path_connected_component, rule_format]) 

689 
using `e>0` as 

690 
apply auto 

691 
done 

692 
qed 

693 
qed 

36583  694 

695 
lemma open_non_path_component: 

696 
fixes s :: "'a::real_normed_vector set" (*TODO: generalize to metric_space*) 

49653  697 
assumes "open s" 
698 
shows "open(s  {y. path_component s x y})" 

699 
unfolding open_contains_ball 

700 
proof 

701 
fix y 

702 
assume as: "y\<in>s  {y. path_component s x y}" 

703 
then obtain e where e:"e>0" "ball y e \<subseteq> s" 

704 
using assms [unfolded open_contains_ball] by auto 

705 
show "\<exists>e>0. ball y e \<subseteq> s  {y. path_component s x y}" 

706 
apply (rule_tac x=e in exI) 

707 
apply (rule, rule `e>0`, rule, rule) defer 

708 
proof (rule ccontr) 

709 
fix z 

710 
assume "z \<in> ball y e" "\<not> z \<notin> {y. path_component s x y}" 

711 
hence "y \<in> {y. path_component s x y}" 

712 
unfolding not_not mem_Collect_eq using `e>0` 

713 
apply  

714 
apply (rule path_component_trans, assumption) 

715 
apply (rule path_component_of_subset[OF e(2)]) 

716 
apply (rule convex_imp_path_connected[OF convex_ball, unfolded path_connected_component, rule_format]) 

717 
apply auto 

718 
done 

719 
thus False using as by auto 

720 
qed (insert e(2), auto) 

721 
qed 

36583  722 

723 
lemma connected_open_path_connected: 

724 
fixes s :: "'a::real_normed_vector set" (*TODO: generalize to metric_space*) 

49653  725 
assumes "open s" "connected s" 
726 
shows "path_connected s" 

727 
unfolding path_connected_component_set 

728 
proof (rule, rule, rule path_component_subset, rule) 

729 
fix x y 

730 
assume "x \<in> s" "y \<in> s" 

731 
show "y \<in> {y. path_component s x y}" 

732 
proof (rule ccontr) 

733 
assume "y \<notin> {y. path_component s x y}" 

734 
moreover 

735 
have "{y. path_component s x y} \<inter> s \<noteq> {}" 

736 
using `x\<in>s` path_component_eq_empty path_component_subset[of s x] by auto 

737 
ultimately 

738 
show False 

739 
using `y\<in>s` open_non_path_component[OF assms(1)] open_path_component[OF assms(1)] 

740 
using assms(2)[unfolded connected_def not_ex, rule_format, of"{y. path_component s x y}" "s  {y. path_component s x y}"] 

741 
by auto 

742 
qed 

743 
qed 

36583  744 

745 
lemma path_connected_continuous_image: 

49653  746 
assumes "continuous_on s f" "path_connected s" 
747 
shows "path_connected (f ` s)" 

748 
unfolding path_connected_def 

749 
proof (rule, rule) 

750 
fix x' y' 

751 
assume "x' \<in> f ` s" "y' \<in> f ` s" 

752 
then obtain x y where xy: "x\<in>s" "y\<in>s" "x' = f x" "y' = f y" by auto 

753 
guess g using assms(2)[unfolded path_connected_def, rule_format, OF xy(1,2)] .. 

36583  754 
thus "\<exists>g. path g \<and> path_image g \<subseteq> f ` s \<and> pathstart g = x' \<and> pathfinish g = y'" 
49653  755 
unfolding xy 
756 
apply (rule_tac x="f \<circ> g" in exI) 

757 
unfolding path_defs 

758 
using assms(1) 

759 
apply (auto intro!: continuous_on_compose continuous_on_subset[of _ _ "g ` {0..1}"]) 

760 
done 

761 
qed 

36583  762 

763 
lemma homeomorphic_path_connectedness: 

764 
"s homeomorphic t \<Longrightarrow> (path_connected s \<longleftrightarrow> path_connected t)" 

49653  765 
unfolding homeomorphic_def homeomorphism_def 
766 
apply (erule exEerule conjE)+ 

767 
apply rule 

768 
apply (drule_tac f=f in path_connected_continuous_image) prefer 3 

769 
apply (drule_tac f=g in path_connected_continuous_image) 

770 
apply auto 

771 
done 

36583  772 

773 
lemma path_connected_empty: "path_connected {}" 

774 
unfolding path_connected_def by auto 

775 

776 
lemma path_connected_singleton: "path_connected {a}" 

777 
unfolding path_connected_def pathstart_def pathfinish_def path_image_def 

778 
apply (clarify, rule_tac x="\<lambda>x. a" in exI, simp add: image_constant_conv) 

779 
apply (simp add: path_def continuous_on_const) 

780 
done 

781 

49653  782 
lemma path_connected_Un: 
783 
assumes "path_connected s" "path_connected t" "s \<inter> t \<noteq> {}" 

784 
shows "path_connected (s \<union> t)" 

785 
unfolding path_connected_component 

786 
proof (rule, rule) 

787 
fix x y 

788 
assume as: "x \<in> s \<union> t" "y \<in> s \<union> t" 

36583  789 
from assms(3) obtain z where "z \<in> s \<inter> t" by auto 
49653  790 
thus "path_component (s \<union> t) x y" 
791 
using as and assms(12)[unfolded path_connected_component] 

792 
apply  

793 
apply (erule_tac[!] UnE)+ 

794 
apply (rule_tac[23] path_component_trans[of _ _ z]) 

795 
apply (auto simp add:path_component_of_subset [OF Un_upper1] path_component_of_subset[OF Un_upper2]) 

796 
done 

797 
qed 

36583  798 

37674
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convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

799 
lemma path_connected_UNION: 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

800 
assumes "\<And>i. i \<in> A \<Longrightarrow> path_connected (S i)" 
49653  801 
and "\<And>i. i \<in> A \<Longrightarrow> z \<in> S i" 
37674
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

802 
shows "path_connected (\<Union>i\<in>A. S i)" 
49653  803 
unfolding path_connected_component 
804 
proof clarify 

37674
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

805 
fix x i y j 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

806 
assume *: "i \<in> A" "x \<in> S i" "j \<in> A" "y \<in> S j" 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

807 
hence "path_component (S i) x z" and "path_component (S j) z y" 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

808 
using assms by (simp_all add: path_connected_component) 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

809 
hence "path_component (\<Union>i\<in>A. S i) x z" and "path_component (\<Union>i\<in>A. S i) z y" 
48125
602dc0215954
tuned proofs  prefer direct "rotated" instead of oldstyle COMP;
wenzelm
parents:
44647
diff
changeset

810 
using *(1,3) by (auto elim!: path_component_of_subset [rotated]) 
37674
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

811 
thus "path_component (\<Union>i\<in>A. S i) x y" 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

812 
by (rule path_component_trans) 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

813 
qed 
36583  814 

49653  815 

37674
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

816 
subsection {* sphere is pathconnected. *} 
37489
44e42d392c6e
Introduce a type class for euclidean spaces, port most lemmas from real^'n to this type class.
hoelzl
parents:
36583
diff
changeset

817 

36583  818 
lemma path_connected_punctured_universe: 
37674
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

819 
assumes "2 \<le> DIM('a::euclidean_space)" 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

820 
shows "path_connected((UNIV::'a::euclidean_space set)  {a})" 
49653  821 
proof  
37674
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

822 
let ?A = "{x::'a. \<exists>i\<in>{..<DIM('a)}. x $$ i < a $$ i}" 
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convert theorem path_connected_sphere to euclidean_space class
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parents:
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diff
changeset

823 
let ?B = "{x::'a. \<exists>i\<in>{..<DIM('a)}. a $$ i < x $$ i}" 
36583  824 

49653  825 
have A: "path_connected ?A" 
826 
unfolding Collect_bex_eq 

37674
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

827 
proof (rule path_connected_UNION) 
49653  828 
fix i 
829 
assume "i \<in> {..<DIM('a)}" 

37674
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convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

830 
thus "(\<chi>\<chi> i. a $$ i  1) \<in> {x::'a. x $$ i < a $$ i}" by simp 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

831 
show "path_connected {x. x $$ i < a $$ i}" unfolding euclidean_component_def 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

832 
by (rule convex_imp_path_connected [OF convex_halfspace_lt]) 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

833 
qed 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

834 
have B: "path_connected ?B" unfolding Collect_bex_eq 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

835 
proof (rule path_connected_UNION) 
49653  836 
fix i 
837 
assume "i \<in> {..<DIM('a)}" 

37674
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

838 
thus "(\<chi>\<chi> i. a $$ i + 1) \<in> {x::'a. a $$ i < x $$ i}" by simp 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

839 
show "path_connected {x. a $$ i < x $$ i}" unfolding euclidean_component_def 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

840 
by (rule convex_imp_path_connected [OF convex_halfspace_gt]) 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

841 
qed 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

842 
from assms have "1 < DIM('a)" by auto 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

843 
hence "a + basis 0  basis 1 \<in> ?A \<inter> ?B" by auto 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

844 
hence "?A \<inter> ?B \<noteq> {}" by fast 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

845 
with A B have "path_connected (?A \<union> ?B)" 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

846 
by (rule path_connected_Un) 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

847 
also have "?A \<union> ?B = {x. \<exists>i\<in>{..<DIM('a)}. x $$ i \<noteq> a $$ i}" 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

848 
unfolding neq_iff bex_disj_distrib Collect_disj_eq .. 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

849 
also have "\<dots> = {x. x \<noteq> a}" 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

850 
unfolding Bex_def euclidean_eq [where 'a='a] by simp 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

851 
also have "\<dots> = UNIV  {a}" by auto 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

852 
finally show ?thesis . 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

853 
qed 
36583  854 

37674
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

855 
lemma path_connected_sphere: 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
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parents:
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diff
changeset

856 
assumes "2 \<le> DIM('a::euclidean_space)" 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

857 
shows "path_connected {x::'a::euclidean_space. norm(x  a) = r}" 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

858 
proof (rule linorder_cases [of r 0]) 
49653  859 
assume "r < 0" 
860 
hence "{x::'a. norm(x  a) = r} = {}" by auto 

37674
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

861 
thus ?thesis using path_connected_empty by simp 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

862 
next 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

863 
assume "r = 0" 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
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diff
changeset

864 
thus ?thesis using path_connected_singleton by simp 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

865 
next 
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

866 
assume r: "0 < r" 
49653  867 
hence *: "{x::'a. norm(x  a) = r} = (\<lambda>x. a + r *\<^sub>R x) ` {x. norm x = 1}" 
868 
apply  

869 
apply (rule set_eqI, rule) 

870 
unfolding image_iff 

871 
apply (rule_tac x="(1/r) *\<^sub>R (x  a)" in bexI) 

872 
unfolding mem_Collect_eq norm_scaleR 

873 
apply (auto simp add: scaleR_right_diff_distrib) 

874 
done 

875 
have **: "{x::'a. norm x = 1} = (\<lambda>x. (1/norm x) *\<^sub>R x) ` (UNIV  {0})" 

876 
apply (rule set_eqI,rule) 

877 
unfolding image_iff 

878 
apply (rule_tac x=x in bexI) 

879 
unfolding mem_Collect_eq 

880 
apply (auto split:split_if_asm) 

881 
done 

44647
e4de7750cdeb
modernize lemmas about 'continuous' and 'continuous_on';
huffman
parents:
44531
diff
changeset

882 
have "continuous_on (UNIV  {0}) (\<lambda>x::'a. 1 / norm x)" 
e4de7750cdeb
modernize lemmas about 'continuous' and 'continuous_on';
huffman
parents:
44531
diff
changeset

883 
unfolding field_divide_inverse by (simp add: continuous_on_intros) 
36583  884 
thus ?thesis unfolding * ** using path_connected_punctured_universe[OF assms] 
49653  885 
by (auto intro!: path_connected_continuous_image continuous_on_intros) 
37674
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

886 
qed 
36583  887 

37674
f86de9c00c47
convert theorem path_connected_sphere to euclidean_space class
huffman
parents:
37489
diff
changeset

888 
lemma connected_sphere: "2 \<le> DIM('a::euclidean_space) \<Longrightarrow> connected {x::'a. norm(x  a) = r}" 
36583  889 
using path_connected_sphere path_connected_imp_connected by auto 
890 

891 
end 