proposition: Lemma prefix_concat: forall xs ys zs, prefix xs ys -> prefix xs (ys ++ zs).
proof: Proof. Proof using. unfold prefix. introv (ws&?). subst ys. exists (ws ++ zs). rew_list. eauto. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation LibList)