proposition: Lemma binds_app_iff : binds x a (E ++ F) <-> binds x a E \/ binds x a F.
proof: Proof. clear. unfold binds. rewrite in_app_iff. split; auto. Qed.
imports: Coq.FSets.FSets Coq.Lists.List Coq.Logic.Decidable Coq.Strings.String String Metalib.CoqFSetDecide Metalib.CoqListFacts Metalib.LibTactics Metalib.CoqFSetInterface Coq.Classes.Equivalence Coq.Classes.EquivDec Metalib.CoqEqDec