proposition: Lemma mem_last_eq : forall x y l, mem x (l&y) = (mem x l \/ x = y).
proof: Proof. Proof using. intros. rewrite mem_app_eq. rewrite~ mem_one_eq. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation)