proposition: Lemma app_cons_r : forall x l1 l2, l1 ++ (x::l2) = (l1 & x) ++ l2.
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)