intros x y H'; red in |- *.
apply Rplus_lt_reg_r with (r := (- y)%R).
repeat rewrite (Rplus_comm (- y)).
rewrite Rplus_opp_r.
change (x - y < 0)%R in |- *.
rewrite <- Fdiff_correct.
replace 0%R with (powerRZ radix (Zmin (Fexp x) (Fexp y)) * 0)%R;
auto with real arith.
rewrite (Rmult_comm (Fdiff x y)).
apply Rmult_lt_compat_l; auto with real zarith.
replace 0%R with (IZR 0); auto with real arith.
apply Rlt_IZR; red in |- *.
generalize H'; unfold Flt_bool, Fcompare in |- *.
case (Fdiff x y ?= 0)%Z; auto; intros; try discriminate.
Qed.

Theorem Flt_bool_correct_r :
forall x y : float, Flt x y -> Flt_bool x y = true.