I think most of us Europeans are used to Japanese rules, but don’t know the hidden rulings and the reasons behind them. (I won’t bother introducing the basic rules because you probably know them.)
Japanese rules are the epitome of territory scoring. As such, playing in you own territory (even after dame) loses points. This comes with the inherent problem of not being able to solve life-and-death disputes, after the end of the game, elegantly without losing points.
In this post I am citing from The Go Player’s Almanac (Richard Bozulich 1992: 230-242), chapter “The Japanese Rules” compiled by James Davies, to back up what I learned at the EGF referee’s workshop at EGC 2017.
In case of disputes
What happens if players do not agree on the life-and-death of stones? Article 9 (end of the game), 3. states:
“If a player requests resumption of a stopped game, his opponent must oblige and has the right to play first.” (Almanac 1992: 230)
This seems reasonable enough, but in certain cases (like the simple example below), no side would want the opponent to play first. In this case, Japanese rules solve it thusly: “Suppose both players would lose if their opponent played ‘a’, so neither requests resumption of the game. Then […] both players lose.” (Almanac 1992: 237)
Bent Four ruled dead
This version of the rule book does not explicitly mention Bent Four. It is ruled dead nonetheless because Article 7 (life and death), 2. says:
“In the confirmation of life and death after the game stops in Article 9, recapturing in the same ko is prohibited. A player […] may, however, capture in that ko again after passing once for that particular ko capture.” (Almanac 1992: 230)
To explain this, below is the shape that occurs when White is proving Black’s Bent Four dead.After White takes at A, Black’s only ko threat is to pass. “Even if [Black] has unlimited ko threats (in a double-ko seki for example), he cannot use them to recapture a ko.” (Almanac 1992: 234)
So after Black has passed, White can take all the stones off the board. (Unless White forgets to take, after which the rules allow Black to recapture the ko and White then has to pass.)
By extension, Black is alive in this very similar yet completely different shape.If the game ends without White actually fighting the approach-move ko, White’s stone is dead and Black is alive without adding a move at A (and thus saves a point). (ibidem)If White wants to kill, White has to take at 1, and Black passes because rules. Then White continues at 3. Now it is legal for Black to recapture at A because Black has passed once. So after Black A, White has to pass and Black captures the white stones.
You probably knew before that Bent Four is dead, but not why. This is thanks to the extra rule that prohibits any ko threats except passing in the after-game stage.
That’s enough on dead groups.
You should know approximately what a seki is, but not the details in Japanese rules. According to Article 8 (territory), “Stones which are alive but possess dame are said to be in seki“. This section also holds the definition of territory to be “Eye points surrounded by stones that are alive but not in seki”. (Almanac 1992: 230)
This means, nobody has territory in the diagramme below.Both White’s corner and Black’s two-eyed group are indisputably alive, but they are in seki because of the shared dame at A. So the territories don’t count.
Here I should mention that, if you are planning on using this knowledge to cheat in a tournament game in Europe, this fortunately does not work 🙂
European tournaments do not use the super hardcore Japanese rules per se, but the EGF General Tournament Rules under which territory scoring is one of the options, albeit the most popular one. They are not as exact as other rule books, but founded on common sense and sportsmanship. Cheating is bad.
That said, the following position is a seki with points (?) which I find somewhat contradictory in the Japanese rules:Whoever plays at A first will get a worse result than having the opponent play there. It is somehow determined that White has 3 points in this position if nobody resolves it until the end of the game.
This extends to similar positions such as this one.So if White is smart, here White will take at A instead of accepting the 3 points.