A Rule For Seki

British Go Journal No. 12. August 1970. Page 5.

Segoe

This article, by Segoe, may be considered as a follow-up to the articles by Fukuda on counting liberties which have appeared in the last two issues. You will remember that these articles specifically avoided the consideration of situations where ko or seki might arise. This article deals with the latter problem.

Diagram 1

Dia 1 shows a situation in which a white group and a black group are in conflict and without eyes. However, the two groups have two liberties in common. Will one die or will both live in seki?

First, we must count the unshared liberties of the groups. White has 6 and black has 5. Thus the white group is stronger and must live. But is the black group dead?

The following rule will solve our problem. Let the number of unshared liberties of the stronger group be X, and the total number of liberties of the weaker group be Y. (In this example X=6 and Y=7, 5 outside plus the two shared.)

Then

1. If X = Y, the stronger group wins, no matter who plays first.
2. If X = Y-1, the stronger kills if he plays first, but it is seki if the other begins.
3. If X = Y-2, it is seki no matter who begins.

For other cases then the first moves are no threat and can be ignored until one of these rules applies.

So, in the problem which we started, case 2 applies, and the black group will die if White plays first, but live in seki if Black plays first.

Diagram 2

Can you solve Dia 2?