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2.3.3 Questions of Reinforcement (2)

The 1949 Nihon Kiin Laws state that one reinforcing moves is required in the top left of Dia. 2-8, and no reinforcing move is required in the bottom left, but this too is explained by means of a precedent. The phrase "direct ko," if not actually ambiguous, can be easily misinterpreted, and the ruling is unnatural.

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Dia. 2-8

White has more ko threats in Dia. 2-9-1. Does he have to add reinforcements at 2, 3, and 4 in Dia. 2-9-2? If a pass is not recognized as a ko threat, these reinforcements are unnecessary and White wins by one point, as you may verify.

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Dia. 2-9-1 Dia. 2-9-2

Many people may feel dissatisfied about this. It has been suggested that the final pass should be admitted as a ko threat. Another way is to allow recreation of a former position (by capturing a ko) after two consecutive passes. This leads to the proposal that the game should end with three consecutive passes. The purpose is to avoid anomalies just prior to the end of the game (to use Shimada's expression), but if you leave life and death undefined, the occurrences in question are not necessarily anomalous. Dia. 2-10-1 shows another one. Black has no way to capture the white group in the bottom left. After White 1, Black 2, and White 3, Black can only pass. White also passes. If you do not admit exceptions to the rule that a pass is not a ko threat, the game ends as in Dia. 2-10-2 and the bottom left white group stays on the board (is alive).

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Dia. 2-10-1 Dia. 2-10-2

If exceptions are admitted after two consecutive passes, further unusual positions can occur. We will return to these when we come to the subject of ko and its generalization.*

*
Under the 1989 Japanese Rules of Go, Black needs to reinforce at both 1 and 2 in Dia. 2-6. After Dia. 2-7-3 White must make two further moves to capture all the black stones in the bottom right corner. White 2, 3, and 4 in Dia. 2-9-2 are also necessary. The white group in the bottom left of Dia. 2-10-2 is dead.
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