Proof with auto with typeclass_instances.
intros x.
apply relative_error_le_conversion...
apply Rlt_le.
apply Rmult_lt_0_compat.
apply Rinv_0_lt_compat.
now apply (Z2R_lt 0 2).
apply bpow_gt_0.
now apply relative_error_N_FLX.
Qed.

Theorem relative_error_N_FLX_round :
forall x,
(Rabs (round beta (FLX_exp prec) (Znearest choice) x - x) <= /2 * bpow (-prec + 1) * Rabs (round beta (FLX_exp prec) (Znearest choice) x))%R.