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;
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(*  Title:      HOL/Library/Permutation.thy
Author:     Lawrence C Paulson and Thomas M Rasmussen and Norbert Voelker
*)

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
```