|Kurotaki Masanori||Kono Mitsuki||1989-01-28||sgf||(insei)|
|Rin Kaiho||Komatsu Hideki||1993-09-02||sgf|
|Takizawa Yuta||Tanaka Yasunori||2003-09-28||sgf||(amateur)|
|Uchida Shuhei||O Meien||2009-09-14||sgf|
|An Sungjoon||Choi Cheolhan||2013-06-29||sgf|
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Here Black 4 is forced, for if White plays there, Black is dead. After White 7 the situation is the same as after White 3. A repetition with period 4.
But Black 2 was a mistake, and he should have connected instead:
with or .
A different situation, involving an additional ko. The Black group on the left doesn't have eyes, and Black has to kill White before he is killed himself. White can sacrifice two stones as a ko threat, and then Black can sacrifice two stones as a ko threat, and the situation repeats (with period 6). On the other hand, instead of 5 at B1, Black could have played 5 at B4:
and since White has no threats, Black would have won. (No threats, that is to say, no threats other than a pass. There are no further points, and Black is 0.5 points ahead. If this is the end of the game, and the remaining four White stones are just declared dead, he wins. If Black actually captures the four White stones, he loses by 0.5 point. So the precise rules about the end of a game play a role here.)
After Black 7 the situation is the same as after Black 1 (period 6 again). Also here both players sacrifice two stones as ko threats.
Precisely the same situation as in the first example. It also occurred in a 2003-09-28 amateur game.
A mirrored version occurred in a 2007-12-28 amateur game: