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Superko
    Keywords: Ko, Rules

The superko rule says that it is forbidden to repeat a previous situation. There are two versions of this: 'positional superko', where it is forbidden to repeat a board position, and 'situational superko', where it is only forbidden to repeat a board position with the same player to move.[1] Many rulesets have some form of superko rule (e.g., AGA rules and New Zealand rules), but other rulesets do not (e.g., Japanese rules, Korean rules and Ing rules).

See also: [ext] http://home.snafu.de/jasiek/superko.html


DavidPeklak : Everybody says situations where this rule has to be applied hardly occur, but one occurred in one of my games recently, although I started playing Go only four months ago...

[Diagram]
Diag.: Superko

The situation seemed to be seki. Probably attempting to kill the black group, White played at a. Black had to capture by playing at b. Now White played at the marked stone again, which gave the original seki position again. This move would have been forbidden if the positional superko rule applies. In that case, Black could have played there after White elsewhere and kill the white stones. I think this is a nice example other than the triple ko situation.



You are right. Situations like these are quite common. Although the superko rule is often quoted when talking about double or triple kos, it can be applied in many other circumstances as well.

In this case, White has gained nothing. He loses sente, and after the sequence he has lost two stones, wheras Black has only lost one. A net loss of sente and a point - not very good :^)

However, the white move at a is an example of an unremovable ko threat - there is nothing Black can do to stop White from using it as a ko threat.

--MortenPahle


[1] BillSpight: There are also versions of the superko rule that take passes into account, such as the earliest superko rule proposed, by Yasunaga Hajime in an article in Kido in 1929.

''Article 7: The repetition of the same pattern shall be prohibited unless the right to an alternate move is disregarded.''

Quoted at [ext] http://www.goban.demon.co.uk/go/shimada/intro.html

In modern terms, "disregarding the right to an alternate play" means passing. When a pass lifts a ko or superko ban, this is sometimes called "pass for ko threat". There are different versions of the superko rule in which an intervening pass allows a repetition. Yasunaga's seems to say that any intervening pass lifts the restriction on repetition, but it may mean a pass by the player who makes the repetition. The interaction with passes can pose problems with ending the game, but not taking passes into account can lead to strange results. My home page, when I get it up, will have a discussion, and my solution to the problem, based on Combinatorial Game Theory.

Meanwhile, here is my solution:

  A board play may not repeat a previous whole board position
  unless a pass has intervened since the last time that position
  occurred.
  Play stops when the same player passes a second time in the
  same board position.

Yasunaga proposed a three-consecutive-pass rule, which is how my solution will usually work. Ing uses a four-pass rule.



This is a copy of the living page "Superko" at Sensei's Library.
(C) the Authors, published under the OpenContent License V1.0.