src/HOL/Library/More_List.thy
changeset 40949 1d46d893d682
parent 39921 45f95e4de831
child 40951 6c35a88d8f61
     1.1 --- a/src/HOL/Library/More_List.thy	Fri Dec 03 22:08:14 2010 +0100
     1.2 +++ b/src/HOL/Library/More_List.thy	Fri Dec 03 22:34:20 2010 +0100
     1.3 @@ -3,7 +3,7 @@
     1.4  header {* Operations on lists beyond the standard List theory *}
     1.5  
     1.6  theory More_List
     1.7 -imports Main
     1.8 +imports Main Multiset
     1.9  begin
    1.10  
    1.11  hide_const (open) Finite_Set.fold
    1.12 @@ -78,10 +78,32 @@
    1.13    "fold g (map f xs) = fold (g o f) xs"
    1.14    by (induct xs) simp_all
    1.15  
    1.16 +lemma fold_remove1_split:
    1.17 +  assumes f: "\<And>x y. x \<in> set xs \<Longrightarrow> y \<in> set xs \<Longrightarrow> f x \<circ> f y = f y \<circ> f x"
    1.18 +    and x: "x \<in> set xs"
    1.19 +  shows "fold f xs = fold f (remove1 x xs) \<circ> f x"
    1.20 +  using assms by (induct xs) (auto simp add: o_assoc [symmetric])
    1.21 +
    1.22 +lemma fold_multiset_equiv:
    1.23 +  assumes f: "\<And>x y. x \<in># multiset_of xs \<Longrightarrow> y \<in># multiset_of xs \<Longrightarrow> f x \<circ> f y = f y \<circ> f x"
    1.24 +    and equiv: "multiset_of xs = multiset_of ys"
    1.25 +  shows "fold f xs = fold f ys"
    1.26 +using f equiv [symmetric] proof (induct xs arbitrary: ys)
    1.27 +  case Nil then show ?case by simp
    1.28 +next
    1.29 +  case (Cons x xs)
    1.30 +  have "\<And>x y. x \<in> set ys \<Longrightarrow> y \<in> set ys \<Longrightarrow> f x \<circ> f y = f y \<circ> f x" 
    1.31 +    by (rule Cons.prems(1)) (simp_all add: mem_set_multiset_eq Cons.prems(2))
    1.32 +  moreover from Cons.prems have "x \<in> set ys" by (simp add: mem_set_multiset_eq)
    1.33 +  ultimately have "fold f ys = fold f (remove1 x ys) \<circ> f x" by (fact fold_remove1_split)
    1.34 +  moreover from Cons.prems have "fold f xs = fold f (remove1 x ys)" by (auto intro: Cons.hyps)
    1.35 +  ultimately show ?case by simp
    1.36 +qed
    1.37 +
    1.38  lemma fold_rev:
    1.39    assumes "\<And>x y. x \<in> set xs \<Longrightarrow> y \<in> set xs \<Longrightarrow> f y \<circ> f x = f x \<circ> f y"
    1.40    shows "fold f (rev xs) = fold f xs"
    1.41 -  using assms by (induct xs) (simp_all del: o_apply add: fold_commute)
    1.42 +  by (rule fold_multiset_equiv, rule assms) (simp_all add: in_multiset_in_set)
    1.43  
    1.44  lemma foldr_fold:
    1.45    assumes "\<And>x y. x \<in> set xs \<Longrightarrow> y \<in> set xs \<Longrightarrow> f y \<circ> f x = f x \<circ> f y"