British Go Journal No. 11.  March 1970. Page 12.
Every Go player has his own idea of the rules of Go, which is satisfactory for all normal situations. Such is the variety of Go, however, that these rules fail in some abnormal situations.
These may arise in two ways: firstly where the normal rules would lead to an infinite cycle of plays which neither player can escape, and secondly where for either player to play in an undefined position would lose him the situation. Two examples of these situations are well known, one of each category, namely ko and seki. The special rules to cover these are equally well known. But there are other equally necessary special rules.
Diagram 1a ||
Diagram 1b ||
Diagram 1c |
A fairly well-known special situation is bent four in the corner. This is apparently seki but can be turned to ko, at the convenience of the player whose stones are in the corner. Therefore the special rule is that the stones are to be considered unconditionally dead, and are removed from the board at the end of the game.
Diagram 2 |
Another situation that has been seen fairly often in books is Chosei, eternal life, which is a four move cycle. The only possible ruling on this position is a draw. The ambitious may like to try the problem in Diagram 2, which is supposed to require 10 minutes for a player of 2nd or 3rd kyu.
A situation which follows a six move cycle is triple ko, which occurs when there are three ko situations, and neither player is prepared to concede two of them. This is considered an extremely bad omen in Japan; one revolt broke out the day after the ruler had a game drawn by triple ko.
Diagram 3a ||
Diagram 3b |
The last situation involving ko is the ten thousand year ko, which sometimes remains to the end of a game. In this case the special rule states that the player who can must take and fill in the ko to make seki.
Diagram 4 |
A kind of double size ko that can lead to a repetitive situation is Junkanko. The unusual feature of this situation is that the first player has the choice of playing for seki if he wishes, or of continuing round the cycle if otherwise the game is unfavourable to him. Again the only ruling possible is a draw, should the cycle be continued.
Diagram 5a ||
Diagram 5b |
A final example of an anomaly is the torazu sanmoku position, which is an example of the problems that the specialty of the corner can create. For either player to play here is disadvantageous, but the position cannot be called a seki, as White, in the particular positions shown, has a definite advantage. Therefore a fair average is taken. The rule also covers extensions of this position, giving White two more points for each Black stone involved.
I hope I have given some idea of the problems that can arise in trying to formulate consistent rules, which cover all possible situations. I would be very glad to hear from anyone who knows of any other special positions such as these, or of any special rulings made by Go authorities to cover these positions.