Definition Fsubnormal (p : float) :=
  Fbounded b p /\
  Fexp p = (- dExp b)%Z /\ (Zabs (radix * Fnum p) < Zpos (vNum b))%Z.

Theorem FsubnormalFexp : forall p : float, Fsubnormal p -> Fexp p = (- dExp b)%Z.