( 978)

(Referenced by 232; 251; 329; 1019)

White did not play at , but at , and Black inserted the Hanezeki Exchange of / . The Punishment Semeai Liberty Level has been reduced by one, and is seven now. Black's group has six liberties (3 * c, 2 * b, k), one less than before, so nothing has changed here (with respect to the relationship of the Main Semeai). Therefore, Black must not connect the hanezeki's tail here, because White's centre group still has five liberties (2 * w, 3 * c); Black will have to re-capture the ko, and so White will win the semeai with Black's connected group on the lower edge.

:
Black has two ko-threats in the hanezeki, one more than before; the second one us suicidal. Black should use the atari in the hanezeki as a ko-threat just now, instead of connecting the hanezeki's tail. Here, only ko-threats are useful that threaten to torpedo White's capturing of the hanezeki's tail.

:
However, reduces Black's liberties below the Punishment Semeai Liberty Level. Please note that White's centre group has five liberties, so Black cannot use the atari of on the upper edge as a ko-threat.

:
White's centre group has four liberties left (2 * w, 2 * c). Therefore, neither , nor (after White has captured in the hanezeki, and Black has re-captured the ko, White needs only four moves at the t-points to capture Black's connected group) will work as a valid ko-threat.

:
Again, Black needed one external ko-threat ( in the diagram; he does not have any in the problem) to win the ko-fight.

Ko: ;

:
If White played at 18 (she would win the semeai with Black's connected group, if Black played the atari of as a ko-threat), would become a valid ko-threat (White's centre group has only three liberties left); these two options are miai.

:
Black wins the semeai in the centre by one move.