(* 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 => 'a list => bool" ("_ <~~> _" [50, 50] 50)
where
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
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 \ 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 \ 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 \# multiset_of ys) = (\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 ==> set xs = set ys"
by (metis multiset_of_eq_perm multiset_of_eq_setD)
lemma perm_distinct_iff: "xs <~~> ys ==> distinct xs = distinct ys"
apply(induct rule:perm.induct)
apply simp_all
apply fastsimp
apply (metis perm_set_eq)
done
end