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Old Semeai
Path: GiveMeLiberties · Prev: EyesThatLoseLiberties · Next: RaceToCaptureInTheCorner
Keywords: Tactics
Temporarily moved here from semeai
Here, both black and white need to avoid capture of their own groups. Since they both have the same number of liberties, whoever has sente will be able to win.
'a' is known as 'shared' liberty, since it is a liberty for both black and white. When attacking your opponents group in a semeai, you should play the shared liberties last. Otherwise, you take away one of your own liberties as well as the opponents, and then give him sente afterwards. In this diagram both groups have 5 liberties. If black plays first, he will capture the white group first. However, if Black played 'a' instead of 1 he would suddenly have one liberty less than white after white 2. Correct play for black would be e.g. black 1. White should not respond with white 2, since he cannot win anyway. However, it does make a good ko threat.
The presence of eyes in a semeai complicate matters somewhat. In this position, at first glance black seems to have more liberties than white (6 against 5). Nevertheless, black cannot win the semeai even if he plays first. Why this is the case, and how one should correct the count so as to count a semeai like this correctly can be read in EyesWinSemeais. Another complicating factor is that when there are big eyes (four spaces or more), the number of liberties also is higher than a naive count would suggest. See Four Is Five And Five Is Eight And Six Is Twelve or counting liberties for this effect.
Although you can easily count external liberties, sometimes it is necessary to play more than just on the liberties to capture the group. In this example, both players have 3 liberties. However, even with sente, black cannot win the semeai. Black must play 3 before he can play atari at 'a', and by that time he is in atari himself. In practice this approach move has given white one extra liberty. authors:
Path: GiveMeLiberties · Prev: EyesThatLoseLiberties · Next: RaceToCaptureInTheCorner This is a copy of the living page "Old Semeai" at Sensei's Library. ![]() |