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src/HOL/Library/Permutation.thy

author | wenzelm |

Wed, 31 Aug 2005 15:46:37 +0200 | |

changeset 17200 | 3a4d03d1a31b |

parent 15140 | 322485b816ac |

child 19380 | b808efaa5828 |

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

tuned presentation;

(* Title: HOL/Library/Permutation.thy Author: Lawrence C Paulson and Thomas M Rasmussen and Norbert Voelker *) header {* Permutations *} theory Permutation imports Multiset begin consts perm :: "('a list * 'a list) set" syntax "_perm" :: "'a list => 'a list => bool" ("_ <~~> _" [50, 50] 50) translations "x <~~> y" == "(x, y) \<in> perm" inductive perm intros Nil [intro!]: "[] <~~> []" swap [intro!]: "y # x # l <~~> x # y # l" Cons [intro!]: "xs <~~> ys ==> z # xs <~~> z # ys" trans [intro]: "xs <~~> ys ==> ys <~~> zs ==> xs <~~> zs" lemma perm_refl [iff]: "l <~~> l" by (induct l) auto subsection {* Some examples of rule induction on permutations *} lemma xperm_empty_imp_aux: "xs <~~> ys ==> xs = [] --> ys = []" -- {*the form of the premise lets the induction bind @{term xs} and @{term ys} *} apply (erule perm.induct) apply (simp_all (no_asm_simp)) done lemma xperm_empty_imp: "[] <~~> ys ==> ys = []" using xperm_empty_imp_aux by blast text {* \medskip This more general theorem is easier to understand! *} lemma perm_length: "xs <~~> ys ==> length xs = length ys" by (erule perm.induct) simp_all lemma perm_empty_imp: "[] <~~> xs ==> xs = []" by (drule perm_length) auto lemma perm_sym: "xs <~~> ys ==> ys <~~> xs" by (erule perm.induct) auto lemma perm_mem [rule_format]: "xs <~~> ys ==> x mem xs --> x mem ys" by (erule perm.induct) 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 ==> l @ xs <~~> l @ ys" by (induct l) auto lemma perm_append2: "xs <~~> ys ==> 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 [rule_format]: "ys <~~> xs ==> xs = [y] --> ys = [y]" by (erule perm.induct) 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 *} consts remove :: "'a => 'a list => 'a list" primrec "remove x [] = []" "remove x (y # ys) = (if x = y then ys else y # remove x ys)" lemma perm_remove: "x \<in> set ys ==> ys <~~> x # remove x ys" by (induct ys) auto lemma remove_commute: "remove x (remove y l) = remove y (remove x l)" by (induct l) auto lemma multiset_of_remove[simp]: "multiset_of (remove a x) = multiset_of x - {#a#}" apply (induct x) apply (auto simp: multiset_eq_conv_count_eq) done text {* \medskip Congruence rule *} lemma perm_remove_perm: "xs <~~> ys ==> remove z xs <~~> remove z ys" by (erule perm.induct) auto lemma remove_hd [simp]: "remove z (z # xs) = xs" by auto lemma cons_perm_imp_perm: "z # xs <~~> z # ys ==> 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: "!!xs ys. zs @ xs <~~> zs @ ys ==> xs <~~> ys" apply (induct zs rule: rev_induct) apply (simp_all (no_asm_use)) apply blast done 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 = "remove 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) = (\<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 end