proposition: Lemma app_cons A (x : A) xs ys : (x :: xs) ++ ys = x :: (xs ++ ys).
proof: Proof. reflexivity. Qed.
imports: Coq.ZArith.ZArith Coq.Lists.List Coq.Setoids.Setoid Coq.Classes.Morphisms Coq.QArith.QArith_base Coq.QArith.Qreduction Coq.QArith.Qround