intuition.
eapply le_lt_trans.
eapply mult_le_compat.
assert (a <= b).
omega.
eapply H1.
eapply le_refl.
eapply mult_lt_compat_l.
trivial.
omega.
Qed.

Theorem orb_same_eq_if :
forall a b c,
(a = false -> b = c) ->
orb a b = orb a c.