intros p H' H'0.
rewrite <- (Ropp_involutive p); unfold FtoRradix in |- *;
repeat rewrite Fopp_correct.
apply Ropp_le_contravar; rewrite <- Fopp_correct.
apply FnormalLtFirstNormalPos.
apply FnormalFop; auto.
replace 0%R with (-0)%R; unfold FtoRradix in |- *; try rewrite Fopp_correct;
auto with real.
Qed.

Theorem FsubnormalDigit :
forall p : float, Fsubnormal p -> Fdigit radix p < precision.