Proof with auto with typeclass_instances.
intros x Gx.
apply generic_format_abs_inv.
apply generic_format_abs in Gx.
revert rnd valid_rnd x Gx.
refine (round_abs_abs _ (fun x y => generic_format fexp1 x -> generic_format fexp1 y) _).
intros rnd valid_rnd x [Hx|Hx] Gx.
(* x > 0 *)
generalize (ln_beta_generic_gt _ x (Rgt_not_eq _ _ Hx) Gx).
unfold canonic_exp.
destruct (ln_beta beta x) as (ex,Ex) ; simpl.
specialize (Ex (Rgt_not_eq _ _ Hx)).
intros He'.
rewrite Rabs_pos_eq in Ex by now apply Rlt_le.
destruct (Zle_or_lt ex (fexp2 ex)) as [He|He].
(* - x near 0 for fexp2 *)
destruct (round_bounded_small_pos fexp2 rnd x ex He Ex) as [Hr|Hr].
rewrite Hr.
apply generic_format_0.
rewrite Hr.
apply generic_format_bpow'...
apply Zlt_le_weak.
apply valid_exp_large with ex...
(* - x large for fexp2 *)
destruct (Zle_or_lt (canonic_exp fexp2 x) (canonic_exp fexp1 x)) as [He''|He''].
(* - - round fexp2 x is representable for fexp1 *)
rewrite round_generic...
rewrite Gx.
apply generic_format_F2R.
fold (round fexp1 Ztrunc x).
intros Zx.
unfold canonic_exp at 1.
rewrite ln_beta_round_ZR...
contradict Zx.
apply F2R_eq_0_reg with (1 := Zx).
(* - - round fexp2 x has too many digits for fexp1 *)
destruct (round_bounded_large_pos fexp2 rnd x ex He Ex) as (Hr1,[Hr2|Hr2]).
apply generic_format_F2R.
intros Zx.
fold (round fexp2 rnd x).
unfold canonic_exp at 1.
rewrite ln_beta_unique_pos with (1 := conj Hr1 Hr2).
rewrite <- ln_beta_unique_pos with (1 := Ex).
now apply Zlt_le_weak.
rewrite Hr2.
apply generic_format_bpow'...
now apply Zlt_le_weak.
(* x = 0 *)
rewrite <- Hx, round_0...
apply generic_format_0.
Qed.
End Inclusion.
End Generic.
Notation ZnearestA := (Znearest (Zle_bool 0)).
Section rndNA_opp.

Lemma round_NA_opp :
forall beta : radix,
forall (fexp : Z -> Z),
forall x,
(round beta fexp ZnearestA (- x) = - round beta fexp ZnearestA x)%R.