intros f' k l cvf eps ep; destruct (cvf eps ep) as [N Pn].
exists N; intros n nN; apply Pn; auto with arith.
Qed.
(* Growing property is preserved after shifting the indices (one way only) *)

(* Specifications: *)
Lemma Un_growing_shift :
forall k un, Un_growing un -> Un_growing (fun n => un (n + k)%nat).