author  bulwahn 
Thu, 08 Nov 2012 20:02:41 +0100  
changeset 50037  f2a32197a33a 
parent 44890  22f665a2e91c 
child 51542  738598beeb26 
permissions  rwrr 
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(* Title: HOL/Library/Permutation.thy 
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Author: Lawrence C Paulson and Thomas M Rasmussen and Norbert Voelker 
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*) 
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header {* Permutations *} 
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theory Permutation 
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imports Main Multiset 
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begin 
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inductive 
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perm :: "'a list => 'a list => bool" ("_ <~~> _" [50, 50] 50) 

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where 

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Nil [intro!]: "[] <~~> []" 
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 swap [intro!]: "y # x # l <~~> x # y # l" 
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 Cons [intro!]: "xs <~~> ys ==> z # xs <~~> z # ys" 

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 trans [intro]: "xs <~~> ys ==> ys <~~> zs ==> xs <~~> zs" 

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lemma perm_refl [iff]: "l <~~> l" 

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by (induct l) auto 
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subsection {* Some examples of rule induction on permutations *} 

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lemma xperm_empty_imp: "[] <~~> ys ==> ys = []" 

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by (induct xs == "[]::'a list" ys pred: perm) simp_all 
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text {* 

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\medskip This more general theorem is easier to understand! 

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*} 

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lemma perm_length: "xs <~~> ys ==> length xs = length ys" 

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by (induct pred: perm) simp_all 
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lemma perm_empty_imp: "[] <~~> xs ==> xs = []" 

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by (drule perm_length) auto 
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lemma perm_sym: "xs <~~> ys ==> ys <~~> xs" 

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by (induct pred: perm) auto 
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subsection {* Ways of making new permutations *} 

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text {* 

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We can insert the head anywhere in the list. 

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*} 

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lemma perm_append_Cons: "a # xs @ ys <~~> xs @ a # ys" 

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by (induct xs) auto 
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lemma perm_append_swap: "xs @ ys <~~> ys @ xs" 

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apply (induct xs) 
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apply simp_all 

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apply (blast intro: perm_append_Cons) 
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done 

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lemma perm_append_single: "a # xs <~~> xs @ [a]" 

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by (rule perm.trans [OF _ perm_append_swap]) simp 
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lemma perm_rev: "rev xs <~~> xs" 

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apply (induct xs) 
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apply simp_all 

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apply (blast intro!: perm_append_single intro: perm_sym) 
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done 
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lemma perm_append1: "xs <~~> ys ==> l @ xs <~~> l @ ys" 

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by (induct l) auto 
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lemma perm_append2: "xs <~~> ys ==> xs @ l <~~> ys @ l" 

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by (blast intro!: perm_append_swap perm_append1) 
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subsection {* Further results *} 

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lemma perm_empty [iff]: "([] <~~> xs) = (xs = [])" 

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by (blast intro: perm_empty_imp) 
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lemma perm_empty2 [iff]: "(xs <~~> []) = (xs = [])" 

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apply auto 

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apply (erule perm_sym [THEN perm_empty_imp]) 

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done 

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lemma perm_sing_imp: "ys <~~> xs ==> xs = [y] ==> ys = [y]" 
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by (induct pred: perm) auto 

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lemma perm_sing_eq [iff]: "(ys <~~> [y]) = (ys = [y])" 

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by (blast intro: perm_sing_imp) 
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lemma perm_sing_eq2 [iff]: "([y] <~~> ys) = (ys = [y])" 

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by (blast dest: perm_sym) 
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subsection {* Removing elements *} 

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lemma perm_remove: "x \<in> set ys ==> ys <~~> x # remove1 x ys" 
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by (induct ys) auto 
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text {* \medskip Congruence rule *} 

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lemma perm_remove_perm: "xs <~~> ys ==> remove1 z xs <~~> remove1 z ys" 
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by (induct pred: perm) auto 
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lemma remove_hd [simp]: "remove1 z (z # xs) = xs" 
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by auto 
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lemma cons_perm_imp_perm: "z # xs <~~> z # ys ==> xs <~~> ys" 

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by (drule_tac z = z in perm_remove_perm) auto 
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lemma cons_perm_eq [iff]: "(z#xs <~~> z#ys) = (xs <~~> ys)" 

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by (blast intro: cons_perm_imp_perm) 
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lemma append_perm_imp_perm: "zs @ xs <~~> zs @ ys ==> xs <~~> ys" 
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apply (induct zs arbitrary: xs ys rule: rev_induct) 

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apply (simp_all (no_asm_use)) 
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apply blast 

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done 

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lemma perm_append1_eq [iff]: "(zs @ xs <~~> zs @ ys) = (xs <~~> ys)" 

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by (blast intro: append_perm_imp_perm perm_append1) 
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lemma perm_append2_eq [iff]: "(xs @ zs <~~> ys @ zs) = (xs <~~> ys)" 

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apply (safe intro!: perm_append2) 

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apply (rule append_perm_imp_perm) 

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apply (rule perm_append_swap [THEN perm.trans]) 

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 {* the previous step helps this @{text blast} call succeed quickly *} 

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apply (blast intro: perm_append_swap) 

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done 

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lemma multiset_of_eq_perm: "(multiset_of xs = multiset_of ys) = (xs <~~> ys) " 
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apply (rule iffI) 
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apply (erule_tac [2] perm.induct, simp_all add: union_ac) 

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apply (erule rev_mp, rule_tac x=ys in spec) 

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apply (induct_tac xs, auto) 

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apply (erule_tac x = "remove1 a x" in allE, drule sym, simp) 
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apply (subgoal_tac "a \<in> set x") 
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apply (drule_tac z=a in perm.Cons) 

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apply (erule perm.trans, rule perm_sym, erule perm_remove) 

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apply (drule_tac f=set_of in arg_cong, simp) 
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done 

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lemma multiset_of_le_perm_append: 
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"multiset_of xs \<le> multiset_of ys \<longleftrightarrow> (\<exists>zs. xs @ zs <~~> ys)" 
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apply (auto simp: multiset_of_eq_perm[THEN sym] mset_le_exists_conv) 
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apply (insert surj_multiset_of, drule surjD) 
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apply (blast intro: sym)+ 

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done 

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lemma perm_set_eq: "xs <~~> ys ==> set xs = set ys" 
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by (metis multiset_of_eq_perm multiset_of_eq_setD) 
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lemma perm_distinct_iff: "xs <~~> ys ==> distinct xs = distinct ys" 

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apply (induct pred: perm) 
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apply simp_all 

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apply fastforce 
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apply (metis perm_set_eq) 
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done 

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lemma eq_set_perm_remdups: "set xs = set ys ==> remdups xs <~~> remdups ys" 
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apply (induct xs arbitrary: ys rule: length_induct) 
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apply (case_tac "remdups xs", simp, simp) 

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apply (subgoal_tac "a : set (remdups ys)") 

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prefer 2 apply (metis set.simps(2) insert_iff set_remdups) 

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apply (drule split_list) apply(elim exE conjE) 

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apply (drule_tac x=list in spec) apply(erule impE) prefer 2 

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apply (drule_tac x="ysa@zs" in spec) apply(erule impE) prefer 2 

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apply simp 

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apply (subgoal_tac "a#list <~~> a#ysa@zs") 

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apply (metis Cons_eq_appendI perm_append_Cons trans) 

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apply (metis Cons Cons_eq_appendI distinct.simps(2) 
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distinct_remdups distinct_remdups_id perm_append_swap perm_distinct_iff) 
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apply (subgoal_tac "set (a#list) = set (ysa@a#zs) & distinct (a#list) & distinct (ysa@a#zs)") 

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apply (fastforce simp add: insert_ident) 
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apply (metis distinct_remdups set_remdups) 
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apply (subgoal_tac "length (remdups xs) < Suc (length xs)") 
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apply simp 

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apply (subgoal_tac "length (remdups xs) \<le> length xs") 

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apply simp 

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apply (rule length_remdups_leq) 

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done 
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lemma perm_remdups_iff_eq_set: "remdups x <~~> remdups y = (set x = set y)" 

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by (metis List.set_remdups perm_set_eq eq_set_perm_remdups) 
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lemma permutation_Ex_bij: 
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assumes "xs <~~> ys" 

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shows "\<exists>f. bij_betw f {..<length xs} {..<length ys} \<and> (\<forall>i<length xs. xs ! i = ys ! (f i))" 

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using assms proof induct 

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case Nil then show ?case unfolding bij_betw_def by simp 

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next 

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case (swap y x l) 

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show ?case 

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proof (intro exI[of _ "Fun.swap 0 1 id"] conjI allI impI) 

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show "bij_betw (Fun.swap 0 1 id) {..<length (y # x # l)} {..<length (x # y # l)}" 

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by (auto simp: bij_betw_def) 
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fix i assume "i < length(y#x#l)" 
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show "(y # x # l) ! i = (x # y # l) ! (Fun.swap 0 1 id) i" 

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by (cases i) (auto simp: Fun.swap_def gr0_conv_Suc) 

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qed 

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next 

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case (Cons xs ys z) 

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then obtain f where bij: "bij_betw f {..<length xs} {..<length ys}" and 

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perm: "\<forall>i<length xs. xs ! i = ys ! (f i)" by blast 

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let "?f i" = "case i of Suc n \<Rightarrow> Suc (f n)  0 \<Rightarrow> 0" 

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show ?case 

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proof (intro exI[of _ ?f] allI conjI impI) 

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have *: "{..<length (z#xs)} = {0} \<union> Suc ` {..<length xs}" 

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"{..<length (z#ys)} = {0} \<union> Suc ` {..<length ys}" 

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by (simp_all add: lessThan_Suc_eq_insert_0) 
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show "bij_betw ?f {..<length (z#xs)} {..<length (z#ys)}" unfolding * 
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proof (rule bij_betw_combine) 

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show "bij_betw ?f (Suc ` {..<length xs}) (Suc ` {..<length ys})" 

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using bij unfolding bij_betw_def 

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by (auto intro!: inj_onI imageI dest: inj_onD simp: image_compose[symmetric] comp_def) 

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qed (auto simp: bij_betw_def) 

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fix i assume "i < length (z#xs)" 

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then show "(z # xs) ! i = (z # ys) ! (?f i)" 

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using perm by (cases i) auto 

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qed 

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next 

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case (trans xs ys zs) 

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then obtain f g where 

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bij: "bij_betw f {..<length xs} {..<length ys}" "bij_betw g {..<length ys} {..<length zs}" and 

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perm: "\<forall>i<length xs. xs ! i = ys ! (f i)" "\<forall>i<length ys. ys ! i = zs ! (g i)" by blast 

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show ?case 

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proof (intro exI[of _ "g\<circ>f"] conjI allI impI) 

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show "bij_betw (g \<circ> f) {..<length xs} {..<length zs}" 

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using bij by (rule bij_betw_trans) 

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fix i assume "i < length xs" 

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with bij have "f i < length ys" unfolding bij_betw_def by force 

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with `i < length xs` show "xs ! i = zs ! (g \<circ> f) i" 

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using trans(1,3)[THEN perm_length] perm by force 

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qed 

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qed 

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end 