Proof with auto with typeclass_instances.
intros Y.
rewrite d_eq; apply ln_beta_DN...
now rewrite <- d_eq.
Qed.

(* Specifications: *)
Lemma Fexp_d: (0 < F2R d)%R -> Fexp d =fexp (ln_beta beta x).
Proof with auto with typeclass_instances.
Lemma Fexp_d: (0 < F2R d)%R -> Fexp d =fexp (ln_beta beta x).
Proof with auto with typeclass_instances.