Definition Fnormalize (p : float) :=
  match Z_zerop (Fnum p) with
  | left _ => Float 0 (- dExp b)
  | right _ =>
      Fshift radix
        (min (precision - Fdigit radix p) (Zabs_nat (dExp b + Fexp p))) p
  end.

Theorem FcanonicPpred : forall x : Z, (- dExp b <= x)%Z -> Fcanonic (Float (pPred (vNum b)) x).