intros H e.
specialize (H (bpow (e-1))).
rewrite ulp_neq_0 in H.
2: apply Rgt_not_eq, bpow_gt_0.
unfold canonic_exp in H.
rewrite ln_beta_bpow in H.
apply generic_format_bpow_inv' in H...
now replace (e-1+1)%Z with e in H by ring.
Qed.

Lemma ulp_ge_ulp_0: Exp_not_FTZ fexp ->
forall x,  (ulp 0 <= ulp x)%R.