proposition: Lemma prefix_closed_prefix: forall ys : list A, prefix_closed (fun xs => prefix xs ys).
proof: Proof. Proof using. intros. rewrite prefix_closure_singleton. eapply prefix_closure_is_prefix_closed. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation LibList)