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: 
nipkow@15131: theory Permutation
wenzelm@51542: imports Multiset
nipkow@15131: begin
wenzelm@11054: 
wenzelm@53238: inductive perm :: "'a list \<Rightarrow> 'a list \<Rightarrow> bool"  ("_ <~~> _"  [50, 50] 50)  (* FIXME proper infix, without ambiguity!? *)
wenzelm@53238: where
wenzelm@53238:   Nil [intro!]: "[] <~~> []"
wenzelm@53238: | swap [intro!]: "y # x # l <~~> x # y # l"
wenzelm@53238: | Cons [intro!]: "xs <~~> ys \<Longrightarrow> z # xs <~~> z # ys"
wenzelm@53238: | trans [intro]: "xs <~~> ys \<Longrightarrow> ys <~~> zs \<Longrightarrow> xs <~~> zs"
wenzelm@11054: 
wenzelm@11054: lemma perm_refl [iff]: "l <~~> l"
wenzelm@17200:   by (induct l) auto
wenzelm@11054: 
wenzelm@11054: 
wenzelm@11054: subsection {* Some examples of rule induction on permutations *}
wenzelm@11054: 
wenzelm@53238: lemma xperm_empty_imp: "[] <~~> ys \<Longrightarrow> ys = []"
wenzelm@56796:   by (induct xs == "[] :: 'a list" ys pred: perm) simp_all
wenzelm@11054: 
wenzelm@11054: 
wenzelm@56796: text {* \medskip This more general theorem is easier to understand! *}
wenzelm@11054: 
wenzelm@53238: lemma perm_length: "xs <~~> ys \<Longrightarrow> length xs = length ys"
wenzelm@25379:   by (induct pred: perm) simp_all
wenzelm@11054: 
wenzelm@53238: lemma perm_empty_imp: "[] <~~> xs \<Longrightarrow> xs = []"
wenzelm@17200:   by (drule perm_length) auto
wenzelm@11054: 
wenzelm@53238: lemma perm_sym: "xs <~~> ys \<Longrightarrow> ys <~~> xs"
wenzelm@25379:   by (induct pred: perm) auto
wenzelm@11054: 
wenzelm@11054: 
wenzelm@11054: subsection {* Ways of making new permutations *}
wenzelm@11054: 
wenzelm@56796: text {* We can insert the head anywhere in the list. *}
wenzelm@11054: 
wenzelm@11054: lemma perm_append_Cons: "a # xs @ ys <~~> xs @ a # ys"
wenzelm@17200:   by (induct xs) auto
wenzelm@11054: 
wenzelm@11054: lemma perm_append_swap: "xs @ ys <~~> ys @ xs"
wenzelm@17200:   apply (induct xs)
wenzelm@17200:     apply 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@17200:   by (rule perm.trans [OF _ perm_append_swap]) simp
wenzelm@11054: 
wenzelm@11054: lemma perm_rev: "rev xs <~~> xs"
wenzelm@17200:   apply (induct xs)
wenzelm@17200:    apply simp_all
paulson@11153:   apply (blast intro!: perm_append_single intro: perm_sym)
wenzelm@11054:   done
wenzelm@11054: 
wenzelm@53238: lemma perm_append1: "xs <~~> ys \<Longrightarrow> l @ xs <~~> l @ ys"
wenzelm@17200:   by (induct l) auto
wenzelm@11054: 
wenzelm@53238: lemma perm_append2: "xs <~~> ys \<Longrightarrow> xs @ l <~~> ys @ l"
wenzelm@17200:   by (blast intro!: perm_append_swap perm_append1)
wenzelm@11054: 
wenzelm@11054: 
wenzelm@11054: subsection {* Further results *}
wenzelm@11054: 
wenzelm@56796: lemma perm_empty [iff]: "[] <~~> xs \<longleftrightarrow> xs = []"
wenzelm@17200:   by (blast intro: perm_empty_imp)
wenzelm@11054: 
wenzelm@56796: lemma perm_empty2 [iff]: "xs <~~> [] \<longleftrightarrow> xs = []"
wenzelm@11054:   apply auto
wenzelm@11054:   apply (erule perm_sym [THEN perm_empty_imp])
wenzelm@11054:   done
wenzelm@11054: 
wenzelm@53238: lemma perm_sing_imp: "ys <~~> xs \<Longrightarrow> xs = [y] \<Longrightarrow> ys = [y]"
wenzelm@25379:   by (induct pred: perm) auto
wenzelm@11054: 
wenzelm@56796: lemma perm_sing_eq [iff]: "ys <~~> [y] \<longleftrightarrow> ys = [y]"
wenzelm@17200:   by (blast intro: perm_sing_imp)
wenzelm@11054: 
wenzelm@56796: lemma perm_sing_eq2 [iff]: "[y] <~~> ys \<longleftrightarrow> ys = [y]"
wenzelm@17200:   by (blast dest: perm_sym)
wenzelm@11054: 
wenzelm@11054: 
wenzelm@11054: subsection {* Removing elements *}
wenzelm@11054: 
wenzelm@53238: lemma perm_remove: "x \<in> set ys \<Longrightarrow> ys <~~> x # remove1 x ys"
wenzelm@17200:   by (induct ys) auto
wenzelm@11054: 
wenzelm@11054: 
wenzelm@11054: text {* \medskip Congruence rule *}
wenzelm@11054: 
wenzelm@53238: lemma perm_remove_perm: "xs <~~> ys \<Longrightarrow> remove1 z xs <~~> remove1 z ys"
wenzelm@25379:   by (induct pred: perm) auto
wenzelm@11054: 
nipkow@36903: lemma remove_hd [simp]: "remove1 z (z # xs) = xs"
paulson@15072:   by auto
wenzelm@11054: 
wenzelm@53238: lemma cons_perm_imp_perm: "z # xs <~~> z # ys \<Longrightarrow> xs <~~> ys"
wenzelm@17200:   by (drule_tac z = z in perm_remove_perm) auto
wenzelm@11054: 
wenzelm@56796: lemma cons_perm_eq [iff]: "z#xs <~~> z#ys \<longleftrightarrow> xs <~~> ys"
wenzelm@17200:   by (blast intro: cons_perm_imp_perm)
wenzelm@11054: 
wenzelm@53238: lemma append_perm_imp_perm: "zs @ xs <~~> zs @ ys \<Longrightarrow> xs <~~> ys"
wenzelm@53238:   by (induct zs arbitrary: xs ys rule: rev_induct) auto
wenzelm@11054: 
wenzelm@56796: lemma perm_append1_eq [iff]: "zs @ xs <~~> zs @ ys \<longleftrightarrow> xs <~~> ys"
wenzelm@17200:   by (blast intro: append_perm_imp_perm perm_append1)
wenzelm@11054: 
wenzelm@56796: lemma perm_append2_eq [iff]: "xs @ zs <~~> ys @ zs \<longleftrightarrow> 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: 
wenzelm@56796: lemma multiset_of_eq_perm: "multiset_of xs = multiset_of ys \<longleftrightarrow> xs <~~> ys"
wenzelm@17200:   apply (rule iffI)
wenzelm@56796:   apply (erule_tac [2] perm.induct)
wenzelm@56796:   apply (simp_all add: union_ac)
wenzelm@56796:   apply (erule rev_mp)
wenzelm@56796:   apply (rule_tac x=ys in spec)
wenzelm@56796:   apply (induct_tac xs)
wenzelm@56796:   apply auto
wenzelm@56796:   apply (erule_tac x = "remove1 a x" in allE)
wenzelm@56796:   apply (drule sym)
wenzelm@56796:   apply simp
wenzelm@17200:   apply (subgoal_tac "a \<in> set x")
wenzelm@53238:   apply (drule_tac z = a in perm.Cons)
wenzelm@56796:   apply (erule perm.trans)
wenzelm@56796:   apply (rule perm_sym)
wenzelm@56796:   apply (erule perm_remove)
wenzelm@56796:   apply (drule_tac f=set_of in arg_cong)
wenzelm@56796:   apply simp
paulson@15005:   done
paulson@15005: 
wenzelm@53238: lemma multiset_of_le_perm_append: "multiset_of xs \<le> multiset_of ys \<longleftrightarrow> (\<exists>zs. xs @ zs <~~> ys)"
wenzelm@17200:   apply (auto simp: multiset_of_eq_perm[THEN sym] mset_le_exists_conv)
wenzelm@56796:   apply (insert surj_multiset_of)
wenzelm@56796:   apply (drule surjD)
paulson@15072:   apply (blast intro: sym)+
paulson@15072:   done
paulson@15005: 
wenzelm@53238: lemma perm_set_eq: "xs <~~> ys \<Longrightarrow> set xs = set ys"
wenzelm@25379:   by (metis multiset_of_eq_perm multiset_of_eq_setD)
nipkow@25277: 
wenzelm@53238: lemma perm_distinct_iff: "xs <~~> ys \<Longrightarrow> distinct xs = distinct ys"
wenzelm@25379:   apply (induct pred: perm)
wenzelm@25379:      apply simp_all
nipkow@44890:    apply fastforce
wenzelm@25379:   apply (metis perm_set_eq)
wenzelm@25379:   done
nipkow@25277: 
wenzelm@53238: lemma eq_set_perm_remdups: "set xs = set ys \<Longrightarrow> remdups xs <~~> remdups ys"
wenzelm@25379:   apply (induct xs arbitrary: ys rule: length_induct)
wenzelm@53238:   apply (case_tac "remdups xs")
wenzelm@53238:    apply simp_all
wenzelm@53238:   apply (subgoal_tac "a \<in> set (remdups ys)")
blanchet@57816:    prefer 2 apply (metis list.set(2) insert_iff set_remdups)
wenzelm@56796:   apply (drule split_list) apply (elim exE conjE)
wenzelm@56796:   apply (drule_tac x = list in spec) apply (erule impE) prefer 2
wenzelm@56796:    apply (drule_tac x = "ysa @ zs" in spec) apply (erule impE) prefer 2
wenzelm@25379:     apply simp
wenzelm@53238:     apply (subgoal_tac "a # list <~~> a # ysa @ zs")
wenzelm@25379:      apply (metis Cons_eq_appendI perm_append_Cons trans)
haftmann@40122:     apply (metis Cons Cons_eq_appendI distinct.simps(2)
wenzelm@25379:       distinct_remdups distinct_remdups_id perm_append_swap perm_distinct_iff)
wenzelm@56796:    apply (subgoal_tac "set (a # list) =
wenzelm@56796:       set (ysa @ a # zs) \<and> distinct (a # list) \<and> distinct (ysa @ a # zs)")
nipkow@44890:     apply (fastforce simp add: insert_ident)
wenzelm@25379:    apply (metis distinct_remdups set_remdups)
haftmann@30742:    apply (subgoal_tac "length (remdups xs) < Suc (length xs)")
haftmann@30742:    apply simp
haftmann@30742:    apply (subgoal_tac "length (remdups xs) \<le> length xs")
haftmann@30742:    apply simp
haftmann@30742:    apply (rule length_remdups_leq)
wenzelm@25379:   done
nipkow@25287: 
wenzelm@56796: lemma perm_remdups_iff_eq_set: "remdups x <~~> remdups y \<longleftrightarrow> set x = set y"
wenzelm@25379:   by (metis List.set_remdups perm_set_eq eq_set_perm_remdups)
nipkow@25287: 
hoelzl@39075: lemma permutation_Ex_bij:
hoelzl@39075:   assumes "xs <~~> ys"
hoelzl@39075:   shows "\<exists>f. bij_betw f {..<length xs} {..<length ys} \<and> (\<forall>i<length xs. xs ! i = ys ! (f i))"
wenzelm@56796:   using assms
wenzelm@56796: proof induct
wenzelm@53238:   case Nil
wenzelm@56796:   then show ?case
wenzelm@56796:     unfolding bij_betw_def by simp
hoelzl@39075: next
hoelzl@39075:   case (swap y x l)
hoelzl@39075:   show ?case
hoelzl@39075:   proof (intro exI[of _ "Fun.swap 0 1 id"] conjI allI impI)
hoelzl@39075:     show "bij_betw (Fun.swap 0 1 id) {..<length (y # x # l)} {..<length (x # y # l)}"
bulwahn@50037:       by (auto simp: bij_betw_def)
wenzelm@53238:     fix i
wenzelm@56796:     assume "i < length (y # x # l)"
hoelzl@39075:     show "(y # x # l) ! i = (x # y # l) ! (Fun.swap 0 1 id) i"
hoelzl@39075:       by (cases i) (auto simp: Fun.swap_def gr0_conv_Suc)
hoelzl@39075:   qed
hoelzl@39075: next
hoelzl@39075:   case (Cons xs ys z)
wenzelm@56796:   then obtain f where bij: "bij_betw f {..<length xs} {..<length ys}"
wenzelm@56796:     and perm: "\<forall>i<length xs. xs ! i = ys ! (f i)"
wenzelm@56796:     by blast
wenzelm@53238:   let ?f = "\<lambda>i. case i of Suc n \<Rightarrow> Suc (f n) | 0 \<Rightarrow> 0"
hoelzl@39075:   show ?case
hoelzl@39075:   proof (intro exI[of _ ?f] allI conjI impI)
hoelzl@39075:     have *: "{..<length (z#xs)} = {0} \<union> Suc ` {..<length xs}"
hoelzl@39075:             "{..<length (z#ys)} = {0} \<union> Suc ` {..<length ys}"
hoelzl@39078:       by (simp_all add: lessThan_Suc_eq_insert_0)
wenzelm@53238:     show "bij_betw ?f {..<length (z#xs)} {..<length (z#ys)}"
wenzelm@53238:       unfolding *
hoelzl@39075:     proof (rule bij_betw_combine)
hoelzl@39075:       show "bij_betw ?f (Suc ` {..<length xs}) (Suc ` {..<length ys})"
hoelzl@39075:         using bij unfolding bij_betw_def
haftmann@56154:         by (auto intro!: inj_onI imageI dest: inj_onD simp: image_comp comp_def)
hoelzl@39075:     qed (auto simp: bij_betw_def)
wenzelm@53238:     fix i
wenzelm@56796:     assume "i < length (z # xs)"
hoelzl@39075:     then show "(z # xs) ! i = (z # ys) ! (?f i)"
hoelzl@39075:       using perm by (cases i) auto
hoelzl@39075:   qed
hoelzl@39075: next
hoelzl@39075:   case (trans xs ys zs)
wenzelm@56796:   then obtain f g
wenzelm@56796:     where bij: "bij_betw f {..<length xs} {..<length ys}" "bij_betw g {..<length ys} {..<length zs}"
wenzelm@56796:     and perm: "\<forall>i<length xs. xs ! i = ys ! (f i)" "\<forall>i<length ys. ys ! i = zs ! (g i)"
wenzelm@56796:     by blast
hoelzl@39075:   show ?case
wenzelm@53238:   proof (intro exI[of _ "g \<circ> f"] conjI allI impI)
hoelzl@39075:     show "bij_betw (g \<circ> f) {..<length xs} {..<length zs}"
hoelzl@39075:       using bij by (rule bij_betw_trans)
wenzelm@56796:     fix i
wenzelm@56796:     assume "i < length xs"
wenzelm@56796:     with bij have "f i < length ys"
wenzelm@56796:       unfolding bij_betw_def by force
hoelzl@39075:     with `i < length xs` show "xs ! i = zs ! (g \<circ> f) i"
wenzelm@53238:       using trans(1,3)[THEN perm_length] perm by auto
hoelzl@39075:   qed
hoelzl@39075: qed
hoelzl@39075: 
wenzelm@11054: end