Definition Fweight (p : float) :=
  (Fnum p + Fexp p * Zpower_nat radix precision)%Z.

Theorem FinductNeg : forall (P : float -> Prop) (p : float), (0 <= p)%R -> Fcanonic radix b p -> P p -> (forall q : float, Fcanonic radix b q -> (0 < q)%R -> (q <= p)%R -> P q -> P (FPred b radix precision q)) -> forall q : float, Fcanonic radix b q -> (0 <= q)%R -> (q <= p)%R -> P q.