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