proposition: Lemma app_last_r : forall x l1 l2, l1 ++ (l2 & x) = (l1 ++ l2) & x.
proof: Proof. Proof using. intros. rewrite~ <- app_assoc. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation)