proposition: Lemma prefix_concat_simplify: forall xs ys1 ys2, prefix ys1 ys2 -> prefix (xs ++ ys1) (xs ++ ys2).
proof: Proof. Proof using. introv (ws&?). subst ys2. exists ws. rew_list. eauto. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation LibList)