intros p H; unfold Fulp in |- *.
rewrite FcanonicFnormalizeEq; auto with arith.
unfold FtoRradix, FtoR in |- *; simpl in |- *; ring.
Qed.

Theorem FSuccUlpPos :
forall x : float,
Fcanonic radix b x ->
(0 <= x)%R -> Fminus radix (FSucc b radix precision x) x = Fulp x :>R.