intros b p; case (Z_le_gt_dec (Zpos (vNum b)) (Zabs (Fnum p)));
intros H'.
right; red in |- *; intros H'3; Contradict H'; auto with float zarith.
case (Z_le_gt_dec (- dExp b) (Fexp p)); intros H'1.
left; repeat split; auto with zarith.
right; red in |- *; intros H'3; Contradict H'1; auto with float zarith.
Qed.

Theorem FzeroisZero : forall b : Fbound, Fzero (- dExp b) = 0%R :>R.
intros b; unfold FtoRradix, FtoR in |- *; simpl in |- *; auto with real.