Default Restriction Rules

  Difficulty: Expert   Keywords: Ko, Rules, Theory

The Default Restriction Rules are a set of model rules restricting kos and specifying game end conditions. The Default Restriction Rules are sometimes a useful tool for people developing and evaluating the various rule sets for go, used for defining ko in general and quite useful for those wanting to make a catalog of the various ko types occurring in them. A regular player does not need to concern oneself with these definitions at all.


The start-position is the current-position or a particular position.

The 1-play-rule prohibits a cycle consisting of 1 play.

The basic-ko-rule prohibits immediate recapture in a basic-ko.

The fixed-ko-rule prohibits a play to leave position A and create position B if an earlier play left position A and created position B.

The 3-pass-rule ends the game in case of 3 successive passes.

The cycle-end-rule ends the game when a) a situational cycle starting at the start-position occurs and b) a recapture in a basic-ko after exactly 2 successive, intervening passes does not occur.

The Default Restriction Rules are the 1-play-rule, the basic-ko-rule, the fixed-ko-rule, the 3pass-rule, the cycle-end-rule.


A play means board-play. The 1-play-rule prohibits suicide of a single stone. A basic-ko consists of two adjacent intersections on that two successive plays could recreate the position.

The Default Restriction Rules were invented by RobertJasiek in 2008-2010.

The Default Restriction Rules are model rules and a tool for defining especially ko-related terms like in the papers [ext] Ko or [ext] Types of Basic Kos.

An early attempt of defining "ko" and "ko stones" in general had been made by Ing Chang-ki in the Ing Ko Rules by phrases like "can be captured cyclically or repeatedly". This approach was a failure because, as RobertJasiek proved mathematically, each stone in each position can be captured in a cycle when no ko rules are in effect yet. It requires some restriction rules to distinguish interesting ko stones from non-ko-stones. The question was which, and it has turned out that the Default Restriction Rules are suitable. They are in particular because they do allow cycles to occur so that the existing cycles can be identified at all. These rules are also sufficiently liberal to model all practically used ko and game end rules well.

Page creation: RobertJasiek.

Default Restriction Rules last edited by tapir on January 18, 2010 - 16:47
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