wenzelm@11054: (*  Title:      HOL/Library/Permutation.thy
paulson@15005:     Author:     Lawrence C Paulson and Thomas M Rasmussen and Norbert Voelker
wenzelm@11054: *)
wenzelm@11054: 
wenzelm@14706: header {* Permutations *}
wenzelm@11054: 
paulson@15005: theory Permutation = Multiset:
wenzelm@11054: 
wenzelm@11054: consts
wenzelm@11054:   perm :: "('a list * 'a list) set"
wenzelm@11054: 
wenzelm@11054: syntax
wenzelm@11054:   "_perm" :: "'a list => 'a list => bool"    ("_ <~~> _"  [50, 50] 50)
wenzelm@11054: translations
wenzelm@11054:   "x <~~> y" == "(x, y) \<in> perm"
wenzelm@11054: 
wenzelm@11054: inductive perm
paulson@11153:   intros
paulson@11153:     Nil  [intro!]: "[] <~~> []"
paulson@11153:     swap [intro!]: "y # x # l <~~> x # y # l"
paulson@11153:     Cons [intro!]: "xs <~~> ys ==> z # xs <~~> z # ys"
paulson@11153:     trans [intro]: "xs <~~> ys ==> ys <~~> zs ==> xs <~~> zs"
wenzelm@11054: 
wenzelm@11054: lemma perm_refl [iff]: "l <~~> l"
paulson@15005: by (induct l, auto)
wenzelm@11054: 
wenzelm@11054: 
wenzelm@11054: subsection {* Some examples of rule induction on permutations *}
wenzelm@11054: 
wenzelm@11054: lemma xperm_empty_imp_aux: "xs <~~> ys ==> xs = [] --> ys = []"
wenzelm@11054:     -- {* the form of the premise lets the induction bind @{term xs} and @{term ys} *}
wenzelm@11054:   apply (erule perm.induct)
wenzelm@11054:      apply (simp_all (no_asm_simp))
wenzelm@11054:   done
wenzelm@11054: 
wenzelm@11054: lemma xperm_empty_imp: "[] <~~> ys ==> ys = []"
paulson@15005: by (insert xperm_empty_imp_aux, blast)
wenzelm@11054: 
wenzelm@11054: 
wenzelm@11054: text {*
wenzelm@11054:   \medskip This more general theorem is easier to understand!
wenzelm@11054:   *}
wenzelm@11054: 
wenzelm@11054: lemma perm_length: "xs <~~> ys ==> length xs = length ys"
paulson@15005: by (erule perm.induct, simp_all)
wenzelm@11054: 
wenzelm@11054: lemma perm_empty_imp: "[] <~~> xs ==> xs = []"
paulson@15005: by (drule perm_length, auto)
wenzelm@11054: 
wenzelm@11054: lemma perm_sym: "xs <~~> ys ==> ys <~~> xs"
paulson@15005: by (erule perm.induct, auto)
wenzelm@11054: 
wenzelm@11054: lemma perm_mem [rule_format]: "xs <~~> ys ==> x mem xs --> x mem ys"
paulson@15005: by (erule perm.induct, auto)
wenzelm@11054: 
wenzelm@11054: 
wenzelm@11054: subsection {* Ways of making new permutations *}
wenzelm@11054: 
wenzelm@11054: text {*
wenzelm@11054:   We can insert the head anywhere in the list.
wenzelm@11054: *}
wenzelm@11054: 
wenzelm@11054: lemma perm_append_Cons: "a # xs @ ys <~~> xs @ a # ys"
paulson@15005: by (induct xs, auto)
wenzelm@11054: 
wenzelm@11054: lemma perm_append_swap: "xs @ ys <~~> ys @ xs"
paulson@15005:   apply (induct xs, simp_all)
wenzelm@11054:   apply (blast intro: perm_append_Cons)
wenzelm@11054:   done
wenzelm@11054: 
wenzelm@11054: lemma perm_append_single: "a # xs <~~> xs @ [a]"
wenzelm@11054:   apply (rule perm.trans)
wenzelm@11054:    prefer 2
paulson@15005:    apply (rule perm_append_swap, simp)
wenzelm@11054:   done
wenzelm@11054: 
wenzelm@11054: lemma perm_rev: "rev xs <~~> xs"
paulson@15005:   apply (induct xs, simp_all)
paulson@11153:   apply (blast intro!: perm_append_single intro: perm_sym)
wenzelm@11054:   done
wenzelm@11054: 
wenzelm@11054: lemma perm_append1: "xs <~~> ys ==> l @ xs <~~> l @ ys"
paulson@15005: by (induct l, auto)
wenzelm@11054: 
wenzelm@11054: lemma perm_append2: "xs <~~> ys ==> xs @ l <~~> ys @ l"
paulson@15005: by (blast intro!: perm_append_swap perm_append1)
wenzelm@11054: 
wenzelm@11054: 
wenzelm@11054: subsection {* Further results *}
wenzelm@11054: 
wenzelm@11054: lemma perm_empty [iff]: "([] <~~> xs) = (xs = [])"
paulson@15005: by (blast intro: perm_empty_imp)
wenzelm@11054: 
wenzelm@11054: lemma perm_empty2 [iff]: "(xs <~~> []) = (xs = [])"
wenzelm@11054:   apply auto
wenzelm@11054:   apply (erule perm_sym [THEN perm_empty_imp])
wenzelm@11054:   done
wenzelm@11054: 
wenzelm@11054: lemma perm_sing_imp [rule_format]: "ys <~~> xs ==> xs = [y] --> ys = [y]"
paulson@15005: by (erule perm.induct, auto)
wenzelm@11054: 
wenzelm@11054: lemma perm_sing_eq [iff]: "(ys <~~> [y]) = (ys = [y])"
paulson@15005: by (blast intro: perm_sing_imp)
wenzelm@11054: 
wenzelm@11054: lemma perm_sing_eq2 [iff]: "([y] <~~> ys) = (ys = [y])"
paulson@15005: by (blast dest: perm_sym)
wenzelm@11054: 
wenzelm@11054: 
wenzelm@11054: subsection {* Removing elements *}
wenzelm@11054: 
wenzelm@11054: consts
wenzelm@11054:   remove :: "'a => 'a list => 'a list"
wenzelm@11054: primrec
wenzelm@11054:   "remove x [] = []"
wenzelm@11054:   "remove x (y # ys) = (if x = y then ys else y # remove x ys)"
wenzelm@11054: 
wenzelm@11054: lemma perm_remove: "x \<in> set ys ==> ys <~~> x # remove x ys"
paulson@15005: by (induct ys, auto)
wenzelm@11054: 
wenzelm@11054: lemma remove_commute: "remove x (remove y l) = remove y (remove x l)"
paulson@15005: by (induct l, auto)
wenzelm@11054: 
wenzelm@11054: 
wenzelm@11054: text {* \medskip Congruence rule *}
wenzelm@11054: 
wenzelm@11054: lemma perm_remove_perm: "xs <~~> ys ==> remove z xs <~~> remove z ys"
paulson@15005: by (erule perm.induct, auto)
wenzelm@11054: 
wenzelm@11054: lemma remove_hd [simp]: "remove z (z # xs) = xs"
wenzelm@11054:   apply auto
wenzelm@11054:   done
wenzelm@11054: 
wenzelm@11054: lemma cons_perm_imp_perm: "z # xs <~~> z # ys ==> xs <~~> ys"
paulson@15005: by (drule_tac z = z in perm_remove_perm, auto)
wenzelm@11054: 
wenzelm@11054: lemma cons_perm_eq [iff]: "(z#xs <~~> z#ys) = (xs <~~> ys)"
paulson@15005: by (blast intro: cons_perm_imp_perm)
wenzelm@11054: 
wenzelm@11054: lemma append_perm_imp_perm: "!!xs ys. zs @ xs <~~> zs @ ys ==> xs <~~> ys"
wenzelm@11054:   apply (induct zs rule: rev_induct)
wenzelm@11054:    apply (simp_all (no_asm_use))
wenzelm@11054:   apply blast
wenzelm@11054:   done
wenzelm@11054: 
wenzelm@11054: lemma perm_append1_eq [iff]: "(zs @ xs <~~> zs @ ys) = (xs <~~> ys)"
paulson@15005: by (blast intro: append_perm_imp_perm perm_append1)
wenzelm@11054: 
wenzelm@11054: lemma perm_append2_eq [iff]: "(xs @ zs <~~> ys @ zs) = (xs <~~> ys)"
wenzelm@11054:   apply (safe intro!: perm_append2)
wenzelm@11054:   apply (rule append_perm_imp_perm)
wenzelm@11054:   apply (rule perm_append_swap [THEN perm.trans])
wenzelm@11054:     -- {* the previous step helps this @{text blast} call succeed quickly *}
wenzelm@11054:   apply (blast intro: perm_append_swap)
wenzelm@11054:   done
wenzelm@11054: 
paulson@15005: (****************** Norbert Voelker 17 June 2004 **************) 
paulson@15005: 
paulson@15005: consts 
paulson@15005:   multiset_of :: "'a list \<Rightarrow> 'a multiset"
paulson@15005: primrec
paulson@15005:   "multiset_of [] = {#}"
paulson@15005:   "multiset_of (a # x) = multiset_of x + {# a #}"
paulson@15005: 
paulson@15005: lemma multiset_of_zero_iff[simp]: "(multiset_of x = {#}) = (x = [])"
paulson@15005:   by (induct_tac x, auto) 
paulson@15005: 
paulson@15005: lemma multiset_of_zero_iff_right[simp]: "({#} = multiset_of x) = (x = [])"
paulson@15005:   by (induct_tac x, auto)
paulson@15005: 
paulson@15005: lemma set_of_multiset_of[simp]: "set_of(multiset_of x) = set x"
paulson@15005:  by (induct_tac x, auto) 
paulson@15005: 
paulson@15005: lemma multiset_of_remove[simp]: 
paulson@15005:   "multiset_of (remove a x) = multiset_of x - {#a#}"
paulson@15005:   by (induct_tac x, auto simp: multiset_eq_conv_count_eq) 
paulson@15005: 
paulson@15005: lemma multiset_of_eq_perm:  "(multiset_of xs = multiset_of ys) = (xs <~~> ys) "
paulson@15005:   apply (rule iffI) 
paulson@15005:   apply (erule_tac [2] perm.induct, simp_all add: union_ac) 
paulson@15005:   apply (erule rev_mp, rule_tac x=ys in spec, induct_tac xs, auto) 
paulson@15005:   apply (erule_tac x = "remove a x" in allE, drule sym, simp) 
paulson@15005:   apply (subgoal_tac "a \<in> set x") 
paulson@15005:   apply (drule_tac z=a in perm.Cons) 
paulson@15005:   apply (erule perm.trans, rule perm_sym, erule perm_remove) 
paulson@15005:   apply (drule_tac f=set_of in arg_cong, simp)
paulson@15005:   done
paulson@15005: 
paulson@15005: lemma set_count_multiset_of: "set x = {a. 0 < count (multiset_of x) a}"
paulson@15005:   by (induct_tac x, auto)  
paulson@15005: 
paulson@15005: lemma distinct_count_multiset_of: 
paulson@15005:    "distinct x \<Longrightarrow> count (multiset_of x) a = (if a \<in> set x then 1 else 0)"
paulson@15005:   by (erule rev_mp, induct_tac x, auto) 
paulson@15005: 
paulson@15005: lemma distinct_set_eq_iff_multiset_of_eq: 
paulson@15005:   "\<lbrakk>distinct x; distinct y\<rbrakk> \<Longrightarrow> (set x = set y) = (multiset_of x = multiset_of y)"
paulson@15005:   by (auto simp: multiset_eq_conv_count_eq distinct_count_multiset_of) 
paulson@15005: 
wenzelm@11054: end