Judgment of Nyobutsu (如仏の判決)
Judgment of Nyobutsu is a leading case in Kamakura period concerning the life-and-death judgment in the rules of Igo (board game of capturing territory), admitting a kasho (tentative life) in double ko. This judgment is denied in today's rules including the rule of the Nihon Ki-in (the Japanese Go Association). This form is also called 'gekko no katsu' (life in the moonlight).
It is a problem as to the the life or death of a white stone on the right-hand side, in case there is a double-ko (left-hand side) and a white stone with a me and ko (right-hand side) on the same board shown as the figure.
Theory of partial life-and-death
Despite the double ko, the white stone on the right is in 'death'.
Theory of life-and-death in all stages
The white stone is in 'life' since even if the black stone takes the ko on the right, it has endless kozai at the place of double ko and the white always has a chance to get ko back. It is a problem which theory is correct.
The problem was described in the "Kokon Chomon ju" (A Collection of Tales Heard, Past and Present) as an incident that took place those days. In 1253, during the game of two Buddhist monks Hotan-bo and Gyobu-bo, this form appeared. Hotan-bo insisted that it was alive while Gyobu-bo insisted otherwise, and so the problem was not settled. They asked the then Igo master, Hogan Shunkai of Bichu, and received an answer admitting a kasho in double ko (alive). Then they asked Nyobutsu and received an answer saying that it was not the dead stone in double ko although there was a me (alive). As a result, Hotan-bo was admitted as a winner.
Afterwards, the judgment was passed down as the 'Judgment of Nyobutsu.'
Iemoto (the head family of a school) conference
In 1821, a Confucian scholar in Bingofukuyama Domain, Hachiro OTA, asked about this problem to the four iemoto. Honinbo Genjo, Chitokusenchi YASUI, Insainseki INOUE, Genbi HAYASHI and Inshuku HATTORI held a discussion and Genjo announced their answer denying Nyobutsu. This meant that the interpretation of the rules was reversed.
In Meiji period, many Igo players supported the judgment of Nyobutsu (theory of life-and-death in all stages), but Nihon Ki-in adopted the theory of partial life-and-death when it established the rule in 1949. Under China and Taiwan rules (point system rules), the judgment is death from the standpoint of forbidding repeated movement in the game. When the Nihon Ki-in's rule was revised in 1989, the idea was succeeded through the regulation 'forbidding to take back the same ko in the judgment of life-and-death' after the game is finished.
In 1959, in the second game out of three match series between Seigen GO and Hosai FUJISAWA, Go asked for playing the game under the theory of life-and-death in all stages. Go could make this proposal because he was not a member of the Nihon Ki-in. Since Fujisawa approved this, the game became the case which an exceptional rule was adopted. Some people take the view of this as an action to raise a question about the revision of the then Japan Igo rules with several unreasonable points since there was a trouble in the interpretation of the rules concerning the ko at the end of the game of the preceding the second game out of Honinbo three match series between Go and Kaku TAKAGAWA.