proposition: Lemma shiftl_ldiff : forall a b n, (ldiff a b) << n == ldiff (a << n) (b << n).
proof: Proof. intros. bitwise. now rewrite !shiftl_spec, ldiff_spec. Qed.
imports: Bool ZAxioms ZMulOrder ZPow ZDivFloor ZSgnAbs ZParity NZLog