proposition: Lemma mem_last_inv : forall l x y, mem x (l&y) -> (x <> y /\ mem x l) \/ x = y.
proof: Proof. Proof using. introv E. rewrite* mem_last_eq_cases in E. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation)