proposition: Lemma prefix_reflexive: forall xs, prefix xs xs.
proof: Proof. Proof using. intros. exists (@nil A). eapply app_nil_r. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation LibList)