approach play

Those necessary proponent moves that approach opponent stones in order to attack them. In the diagram, Black must not answer white 1 with A. This move would not alter the black group's liberties and White would be able to kill these stones, thus rescuing the marked white stones and killing the marked black stones into the bargain. This is a semeai. The marked stones are in a temporary seki. Although neither White nor Black can kill the other by filling the shared liberties lest they die first, since the black group has one eye and the white has none, as long as Black's outside stones remain uncaptured, Black can win the contest by occupying the white group's outside liberty at B first. However, playing directly at B would merely result in capture of the one black stone. Black must first play an approach move at C. Because of this necessary extra move, Black needs four turns to take off the white stones. Since White also needs precisely four turns to remove the lower unmarked group, Black must not tarry. He must play C straight away.