2.3.2 Connecting a Final Ko
Historically, this question arose in July 1948 in the first game of a
ten-game match between Go and Iwamoto. The question is whether Black,
who has more ko threats, has to play 1 or 2 in Dia. 2-4. The decision
at the time was that White had won by "one or two points,"
but this unprecedented decision was later modified to state that White
had won by one point, because it was found that the provisional Nihon
Kiin rules then in use said, "When one player has more ko threats,
that player does not have to eliminate a final ko at the end of the
game." Still later the Nihon Kiin enacted its 1949 laws, according
to which, "Reinforcement is required in a position that immediately
becomes a direct ko." If that ruling is followed in the game
between Go and Iwamoto, White wins by two points.
Consider the simpler final-ko question in Dia. 2-5. There are no neutral
points, and Black obviously has more ko threats. If it is White's move,
White will either pass or play inside his own territory. If White plays
inside his own territory then of course he loses a point, so Black can
connect at 1 without suffering a net loss.
What if passing is allowed? This can be divided into two cases: one
in which a pass is regarded as a ko threat, and one in which it is
not. The 1949 Nihon Kiin Laws do not fully cover this point, but their
philosophy is close to the idea that a pass is not a ko threat. I agree
that a pass should not be treated as a ko threat, because if passes are
allowed as ko threats, repetition of the same position will occur.*
If we take this position, then when White passes in Dia. 2-5, if Black
also passes, White still cannot play 1. The game therefore ends and the
point at 1 becomes Black's territory.
- Under the 1989 Japanese Rules of Go, Black needs to reinforce at 1 or 2 in Dia. 2-4, and at 1 in Dia. 2-5