Notation bpow e := (bpow beta e).

Lemma error_N_FLT_aux : forall x, (0 < x)%R -> exists eps, exists eta, (Rabs eps <= /2 * bpow (-prec + 1))%R /\ (Rabs eta <= /2 * bpow (emin))%R /\ (eps*eta=0)%R /\ round beta (FLT_exp emin prec) (Znearest choice) x = (x * (1 + eps) + eta)%R.