Notation bpow e := (bpow beta e).

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