Proof with auto with typeclass_instances.
intros choice u v Fu H.
rewrite <- (Ropp_involutive v).
rewrite round_N_opp.
rewrite <- (Ropp_involutive u).
apply Ropp_le_contravar.
apply round_N_le_midp.
now apply generic_format_opp.
apply Ropp_lt_cancel.
rewrite Ropp_involutive.
apply Rle_lt_trans with (2:=H).
unfold pred.
right; field.
Qed.

Lemma round_N_eq_DN: forall choice x,
let d:=round beta fexp Zfloor x in
let u:=round beta fexp Zceil x in
(x<(d+u)/2)%R ->
round beta fexp (Znearest choice) x = d.