Proof with auto with typeclass_instances.
intros e He x (Hx1,[Hx2|Hx2]).
apply generic_inclusion_ln_beta.
now rewrite ln_beta_unique with (1 := conj Hx1 Hx2).
intros Fx.
apply generic_format_abs_inv.
rewrite Hx2.
apply generic_format_bpow'...
apply Zle_trans with (1 := He).
apply generic_format_bpow_inv...
rewrite <- Hx2.
now apply generic_format_abs.
Qed.

Theorem generic_inclusion_le_ge :
forall e1 e2,
(e1 < e2)%Z ->
( forall e, (e1 < e <= e2)%Z -> (fexp2 e <= fexp1 e)%Z ) ->
forall x,
(bpow e1 <= Rabs x <= bpow e2)%R ->
generic_format fexp1 x ->
generic_format fexp2 x.