intros L p H'.
generalize (redacc_cb L nil); simpl in |- *; auto.
rewrite <- app_nil_end; auto.
Qed.

(* Specifications: *)
Theorem cb_redacc :
forall (L1 L2 : list poly) (p : poly), In p L1 -> cb (redacc L1 L2 ++ L2) p.