Capturing race examples
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.
- More accurately, according to Richard Hunter's theory on counting liberties, this is a fight between two groups that share fewer than two liberties. Since they have the same number of exclusive liberties, the side that starts the fight will win.
The point a is known as 'shared' liberty, since it is a liberty for both Black and White.
When attacking your opponent's group in a capturing race, you should play the shared liberties last. Otherwise, you take away one of your own liberties as well as the opponent's, and give him sente.
In this diagram both groups have five liberties. If Black plays first, he will capture the white group first. However, if Black played a instead of he would suddenly have one liberty fewer than White, after .
Correct play for Black would be e.g. . White should not now respond with , since she cannot win anyway. However, it might make a good ko threat.
The presence of eyes in a capturing race 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 capturing race 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 eyes win semeais.
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 moves, not just on the dame liberties, to capture the group.
In this example, both players have three liberties. However, even with sente, Black cannot win the semeai. Black must play before he can play atari at a, and by that time he is in atari himself. In practical terms, this approach move has given White one extra liberty.
- Morten Pahle (10 kyu)
- Arno Hollosi (1 dan)
- Andre Engels (2 dan)