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