: ( 330)
It is not correct for Black to continue with occupying shared liberties.

:
White's group has five liberties now.

If Black had played at , he could occupy a further two outside liberties of White's group, at , and , before White played , forcing Black to connect at . White's group would be reduced to only four liberties.

:
Black does not have any valid ko-threat any more.

White's centre group has four liberties, so Black cannot give atari at on the upper edge. The suicidal atari of in the hanezeki is not available, too, because Black's connected group on the lower edge has only four liberties left.