intros x y H' H'0; try apply sameExpEq; auto.
apply trans_eq with (y := FtoR y); auto.
apply FshiftCorrect.
generalize H' H'0; case x; case y; simpl in |- *; clear H' H'0 x y.
intros Fnum1 Fexp1 Fnum2 Fexp2 H' H'0; rewrite inj_abs; auto with zarith.
Qed.

Theorem FshiftO : forall x : float, Fshift 0 x = x.
intros x; unfold Fshift in |- *; apply floatEq; simpl in |- *.