Notation bpow e := (bpow beta e).(* floating-point format with gradual underflow *)
Definition FLT_format (x : R) :=
  exists f : float beta,
  x = F2R f /\ (Zabs (Fnum f) < Zpower beta prec)%Z /\ (emin <= Fexp f)%Z.Definition FLT_exp e := Zmax (e - prec) emin.(** Properties of the FLT format *)
Global Instance FLT_exp_valid : Valid_exp FLT_exp.

Theorem ulp_FLT_le : forall x, (bpow (emin + prec - 1) <= Rabs x)%R -> (ulp beta FLT_exp x <= Rabs x * bpow (1 - prec))%R.