proposition: Lemma binds_app_3 : binds x a F -> binds x a (E ++ F).
proof: Proof. clear. unfold binds. rewrite in_app_iff. 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