proposition: Lemma map_app : map f1 f2 (E ++ F) = map f1 f2 E ++ map f1 f2 F.
proof: Proof. clear. unfold map. rewrite -> List.map_app. reflexivity. Qed.
imports: Coq.FSets.FSets Coq.Lists.List Coq.Logic.Decidable Metalib.CoqFSetDecide Metalib.CoqListFacts Metalib.LibTactics Metalib.MetatheoryAtom Metalib.LibTactics