proposition: Lemma binds_one_1 : binds x a (y ~ b) -> x = y.
proof: Proof. clear. intros H. inversion H as [HEq | HIn]. inversion HEq; intuition. inversion HIn. 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