apply Rnd_DN_pt_unicity with (generic_format beta fexp) x...
apply round_DN_pt...
Qed.

(* Specifications: *)
Lemma u_eq: F2R u= round beta fexp Zceil x.
Proof with auto with typeclass_instances.
Lemma u_eq: F2R u= round beta fexp Zceil x.
Proof with auto with typeclass_instances.