Definition Pphi_pow :=
   let mkpow x p :=
      match p with xH => x | _ => rpow x (Cp_phi (Npos p)) end in
   let mkopp_pow x p := ropp (mkpow x p)  in
   let mkmult_pow r x p := rmul r (mkpow x p) in
    Pphi_avoid mkpow mkopp_pow mkmult_pow.

Lemma ring_rw_pow_correct : forall n lH l, interp_PElist l lH -> forall lmp, mk_monpol_list lH = lmp -> forall pe npe, norm_subst n lmp pe = npe -> PEeval l pe == Pphi_pow l npe.