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src/HOL/Library/Permutation.thy

author | wenzelm |

Tue, 27 Aug 2013 22:40:39 +0200 | |

changeset 53238 | 01ef0a103fc9 |

parent 51542 | 738598beeb26 |

child 55584 | a879f14b6f95 |

permissions | -rw-r--r-- |

tuned proofs;

(* Title: HOL/Library/Permutation.thy Author: Lawrence C Paulson and Thomas M Rasmussen and Norbert Voelker *) header {* Permutations *} theory Permutation imports Multiset begin inductive perm :: "'a list \<Rightarrow> 'a list \<Rightarrow> bool" ("_ <~~> _" [50, 50] 50) (* FIXME proper infix, without ambiguity!? *) where Nil [intro!]: "[] <~~> []" | swap [intro!]: "y # x # l <~~> x # y # l" | Cons [intro!]: "xs <~~> ys \<Longrightarrow> z # xs <~~> z # ys" | trans [intro]: "xs <~~> ys \<Longrightarrow> ys <~~> zs \<Longrightarrow> xs <~~> zs" lemma perm_refl [iff]: "l <~~> l" by (induct l) auto subsection {* Some examples of rule induction on permutations *} lemma xperm_empty_imp: "[] <~~> ys \<Longrightarrow> ys = []" by (induct xs == "[]::'a list" ys pred: perm) simp_all text {* \medskip This more general theorem is easier to understand! *} lemma perm_length: "xs <~~> ys \<Longrightarrow> length xs = length ys" by (induct pred: perm) simp_all lemma perm_empty_imp: "[] <~~> xs \<Longrightarrow> xs = []" by (drule perm_length) auto lemma perm_sym: "xs <~~> ys \<Longrightarrow> ys <~~> xs" by (induct pred: perm) auto subsection {* Ways of making new permutations *} text {* We can insert the head anywhere in the list. *} lemma perm_append_Cons: "a # xs @ ys <~~> xs @ a # ys" by (induct xs) auto lemma perm_append_swap: "xs @ ys <~~> ys @ xs" apply (induct xs) apply simp_all apply (blast intro: perm_append_Cons) done lemma perm_append_single: "a # xs <~~> xs @ [a]" by (rule perm.trans [OF _ perm_append_swap]) simp lemma perm_rev: "rev xs <~~> xs" apply (induct xs) apply simp_all apply (blast intro!: perm_append_single intro: perm_sym) done lemma perm_append1: "xs <~~> ys \<Longrightarrow> l @ xs <~~> l @ ys" by (induct l) auto lemma perm_append2: "xs <~~> ys \<Longrightarrow> xs @ l <~~> ys @ l" by (blast intro!: perm_append_swap perm_append1) subsection {* Further results *} lemma perm_empty [iff]: "([] <~~> xs) = (xs = [])" by (blast intro: perm_empty_imp) lemma perm_empty2 [iff]: "(xs <~~> []) = (xs = [])" apply auto apply (erule perm_sym [THEN perm_empty_imp]) done lemma perm_sing_imp: "ys <~~> xs \<Longrightarrow> xs = [y] \<Longrightarrow> ys = [y]" by (induct pred: perm) auto lemma perm_sing_eq [iff]: "(ys <~~> [y]) = (ys = [y])" by (blast intro: perm_sing_imp) lemma perm_sing_eq2 [iff]: "([y] <~~> ys) = (ys = [y])" by (blast dest: perm_sym) subsection {* Removing elements *} lemma perm_remove: "x \<in> set ys \<Longrightarrow> ys <~~> x # remove1 x ys" by (induct ys) auto text {* \medskip Congruence rule *} lemma perm_remove_perm: "xs <~~> ys \<Longrightarrow> remove1 z xs <~~> remove1 z ys" by (induct pred: perm) auto lemma remove_hd [simp]: "remove1 z (z # xs) = xs" by auto lemma cons_perm_imp_perm: "z # xs <~~> z # ys \<Longrightarrow> xs <~~> ys" by (drule_tac z = z in perm_remove_perm) auto lemma cons_perm_eq [iff]: "(z#xs <~~> z#ys) = (xs <~~> ys)" by (blast intro: cons_perm_imp_perm) lemma append_perm_imp_perm: "zs @ xs <~~> zs @ ys \<Longrightarrow> xs <~~> ys" by (induct zs arbitrary: xs ys rule: rev_induct) auto lemma perm_append1_eq [iff]: "(zs @ xs <~~> zs @ ys) = (xs <~~> ys)" by (blast intro: append_perm_imp_perm perm_append1) lemma perm_append2_eq [iff]: "(xs @ zs <~~> ys @ zs) = (xs <~~> ys)" apply (safe intro!: perm_append2) apply (rule append_perm_imp_perm) apply (rule perm_append_swap [THEN perm.trans]) -- {* the previous step helps this @{text blast} call succeed quickly *} apply (blast intro: perm_append_swap) done lemma multiset_of_eq_perm: "(multiset_of xs = multiset_of ys) = (xs <~~> ys) " apply (rule iffI) apply (erule_tac [2] perm.induct, simp_all add: union_ac) apply (erule rev_mp, rule_tac x=ys in spec) apply (induct_tac xs, auto) apply (erule_tac x = "remove1 a x" in allE, drule sym, simp) apply (subgoal_tac "a \<in> set x") apply (drule_tac z = a in perm.Cons) apply (erule perm.trans, rule perm_sym, erule perm_remove) apply (drule_tac f=set_of in arg_cong, simp) done lemma multiset_of_le_perm_append: "multiset_of xs \<le> multiset_of ys \<longleftrightarrow> (\<exists>zs. xs @ zs <~~> ys)" apply (auto simp: multiset_of_eq_perm[THEN sym] mset_le_exists_conv) apply (insert surj_multiset_of, drule surjD) apply (blast intro: sym)+ done lemma perm_set_eq: "xs <~~> ys \<Longrightarrow> set xs = set ys" by (metis multiset_of_eq_perm multiset_of_eq_setD) lemma perm_distinct_iff: "xs <~~> ys \<Longrightarrow> distinct xs = distinct ys" apply (induct pred: perm) apply simp_all apply fastforce apply (metis perm_set_eq) done lemma eq_set_perm_remdups: "set xs = set ys \<Longrightarrow> remdups xs <~~> remdups ys" apply (induct xs arbitrary: ys rule: length_induct) apply (case_tac "remdups xs") apply simp_all apply (subgoal_tac "a \<in> set (remdups ys)") prefer 2 apply (metis set.simps(2) insert_iff set_remdups) apply (drule split_list) apply(elim exE conjE) apply (drule_tac x=list in spec) apply(erule impE) prefer 2 apply (drule_tac x="ysa@zs" in spec) apply(erule impE) prefer 2 apply simp apply (subgoal_tac "a # list <~~> a # ysa @ zs") apply (metis Cons_eq_appendI perm_append_Cons trans) apply (metis Cons Cons_eq_appendI distinct.simps(2) distinct_remdups distinct_remdups_id perm_append_swap perm_distinct_iff) apply (subgoal_tac "set (a#list) = set (ysa@a#zs) & distinct (a#list) & distinct (ysa@a#zs)") apply (fastforce simp add: insert_ident) apply (metis distinct_remdups set_remdups) apply (subgoal_tac "length (remdups xs) < Suc (length xs)") apply simp apply (subgoal_tac "length (remdups xs) \<le> length xs") apply simp apply (rule length_remdups_leq) done lemma perm_remdups_iff_eq_set: "remdups x <~~> remdups y \<longleftrightarrow> (set x = set y)" by (metis List.set_remdups perm_set_eq eq_set_perm_remdups) lemma permutation_Ex_bij: assumes "xs <~~> ys" shows "\<exists>f. bij_betw f {..<length xs} {..<length ys} \<and> (\<forall>i<length xs. xs ! i = ys ! (f i))" using assms proof induct case Nil then show ?case unfolding bij_betw_def by simp next case (swap y x l) show ?case proof (intro exI[of _ "Fun.swap 0 1 id"] conjI allI impI) show "bij_betw (Fun.swap 0 1 id) {..<length (y # x # l)} {..<length (x # y # l)}" by (auto simp: bij_betw_def) fix i assume "i < length(y#x#l)" show "(y # x # l) ! i = (x # y # l) ! (Fun.swap 0 1 id) i" by (cases i) (auto simp: Fun.swap_def gr0_conv_Suc) qed next case (Cons xs ys z) then obtain f where bij: "bij_betw f {..<length xs} {..<length ys}" and perm: "\<forall>i<length xs. xs ! i = ys ! (f i)" by blast let ?f = "\<lambda>i. case i of Suc n \<Rightarrow> Suc (f n) | 0 \<Rightarrow> 0" show ?case proof (intro exI[of _ ?f] allI conjI impI) have *: "{..<length (z#xs)} = {0} \<union> Suc ` {..<length xs}" "{..<length (z#ys)} = {0} \<union> Suc ` {..<length ys}" by (simp_all add: lessThan_Suc_eq_insert_0) show "bij_betw ?f {..<length (z#xs)} {..<length (z#ys)}" unfolding * proof (rule bij_betw_combine) show "bij_betw ?f (Suc ` {..<length xs}) (Suc ` {..<length ys})" using bij unfolding bij_betw_def by (auto intro!: inj_onI imageI dest: inj_onD simp: image_compose[symmetric] comp_def) qed (auto simp: bij_betw_def) fix i assume "i < length (z#xs)" then show "(z # xs) ! i = (z # ys) ! (?f i)" using perm by (cases i) auto qed next case (trans xs ys zs) then obtain f g where bij: "bij_betw f {..<length xs} {..<length ys}" "bij_betw g {..<length ys} {..<length zs}" and perm: "\<forall>i<length xs. xs ! i = ys ! (f i)" "\<forall>i<length ys. ys ! i = zs ! (g i)" by blast show ?case proof (intro exI[of _ "g \<circ> f"] conjI allI impI) show "bij_betw (g \<circ> f) {..<length xs} {..<length zs}" using bij by (rule bij_betw_trans) fix i assume "i < length xs" with bij have "f i < length ys" unfolding bij_betw_def by force with `i < length xs` show "xs ! i = zs ! (g \<circ> f) i" using trans(1,3)[THEN perm_length] perm by auto qed qed end