Proof with auto with typeclass_instances.
intros x Hx.
apply relative_error with (emin + prec - 1)%Z...
apply relative_error_FLT_aux.
Qed.

Theorem relative_error_FLT_F2R_emin :
forall m, let x := F2R (Float beta m emin) in
(x <> 0)%R ->
(Rabs (round beta (FLT_exp emin prec) rnd x - x) < bpow (-prec + 1) * Rabs x)%R.