Superko

    Keywords: Ko, Rules

Superko rules prohibit recurrences of an earlier board position under certain circumstances. The recurrence of such positions could be caused by long cycles, such as triple ko, eternal life or round-robin ko.

Table of contents Table of diagrams
Seki

Forms of superko rules

Superko rules come in various forms, depending on when they forbid recreating a board position; factors include:

  • on whose turn the position was previously created;
  • whether players have passed, immediately before or at some intervening time;[1]
  • the type of move recreating the position (see Chinese Superko below).

The main variants in use of the superko rule and other rules on repetitions are:

Superko rule variants
Name of variant Meaning Used in Comments
Positional Superko Forbids a board play to repeat a board position Chinese rules (in theory)
Tromp-Taylor Rules
See Positional Superko / Example
Chinese Superko A play may not repeat a board position by means of basic ko or sending two, returning one Chinese rules (in practice) This, according to the sixth meeting of the International Go Rules Forum,
is what the Chinese rules were intended to specify.
Situational Superko Forbids a board play to repeat a board position with the same player to move (regardless of how it previously arose) AGA rules
New Zealand rules
Natural Situational Superko Forbids a player’s board play to repeat a board position that they created with an earlier board play BGA [ext] Rules 2009

Note that it could allow an immediate ko recapture if the first capture was preceded by a pass.
BGA rules combine this with the basic ko rule to forbid immediate ko recapture.
According to Terry Benson, AGA rules were meant to use Natural Situational Superko, but everybody else interprets them with Situational Superko.

No result If a board position is repeated, the game has “no result” Japanese rules
Korean rules
This usually means the game must be replayed.
Long cycle rule Repetition of a board position ends the game. Computer Olympiad rules (PJT: ¿used with basic ko rule?
The game result depends only on the number of stones captured by either since the first occurrence of the position.

The following variants have been used in theoretical discussions:

Example

The most commonly used example why a superko rule is necessary is triple ko. See below for a more simple case that also illustrates the rule:

[Diagram]
Seki  

This situation is a seki in the corner. Assume Black just passed, so that this position has occurred with either side to play. If White plays at a, Black plays b. With a superko rule in place, White cannot retake at white+circle, so Black can take the corner. Of course, this comes from a White initial mistake, but see Rules Beast 1 for a case where White breaks the seki and wins the fight...


See also

Test cases

Related rules

  • Fixed ko rule: repeated positions may occur but you are not allowed to make the same move in them.
  • Short cycle rules?: The result depends on the number of moves between the repeats. If there are 3 or fewer moves between the repeats the game is a loss for the player who makes the repeat. If there are more moves between the repeats the game is a draw.
  • Long cycle seki rule: The groups involved in a long cycle are treated as alive in seki
  • Colour-blind superko: Ignore the colours, suggested as a ko-rule for multi-colour go.

Further information

Discussions


Notes

[1] Bill Spight: 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.
([ext] http://harryfearnley.com/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, for my solution, see Spight Rules.

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


Superko last edited by PJTraill on March 24, 2019 - 02:03
RecentChanges · StartingPoints · About
Edit page ·Search · Related · Page info · Latest diff
[Welcome to Sensei's Library!]
RecentChanges
StartingPoints
About
RandomPage
Search position
Page history
Latest page diff
Partner sites:
Go Teaching Ladder
Goproblems.com
Login / Prefs
Tools
Sensei's Library