1998-11-30 last update, 1996-08-26 first day; Robert Jasiek
Copyright: All rights of the author are preserved according to the international law.

The New Ko Rules

Introduction

The New Ko Rules are a successor of the Ing 1991 ko rules and furthermore explain them. They are an improvement, because they abandon methodical flaws and use clear definitions and rules.

The New Ko Rules are the rule set that approximates the Ing 1991 ko rules most closely. Therefore it is long and not easy to understand. For a simple rule set of the prohibition rules class please refer to the Basic Ko Rules.

Every published example referring to the Ing ko rules has the same outcome under the New Ko Rules. Perception of the New Ko Rules is eased by Examples 1 and Examples 2.

The New Ko Rules restrict repeatedly cyclical play. Furthermore the rules simplify many difficult and several ko positions on the board by simplifying move-sequences in them, so that they are treated like a basic ko and prohibited board plays can be rather easily detected in actual play.

The major methodical flaws of the Ing 1991 ko rules that are abandoned in the New Ko Rules are as follows:

Due to the flaws in the Ing ko rules it is natural that the New Ko Rules give a slightly different analysis of ko positions. This is the price for gained precision.

There is much scope for variation of definitions and rules, so that still all examples are treated correctly as under Ing ko rules. Especially allowed move-sequences in disturbing kos or for several kos on the board could be defined in many ways. I have used a variation that approaches my knowledge of Ing ko rules as far as possible and that is not logically contradictionary. Unreasonable features of the Ing ko rules have been abandoned. The borders for sets of rules with ko type definitions as to satisfactionary interpretation of any position are illustrated by borderline examples for the New Ko Rules. Similar looking examples have different ko types. The Ing ko rules try to avoid this problem by not using unequivocal definitions.

To appreciate the New Ko Rules the reader should be aware of the great variety of board positions including ko positions.

Abstract of the New Ko Rules: The reader should be familiar with board play and pass play and start by understanding the fundamental definitions like ko mouth. Ko positions may have a ko coupling or not and correspondingly consist of several or only one ko mouths. Many ko positions vary their state between stable and instable. A distinction between fighting ko and disturbing ko is necessary for the rules. The four rules are basic ko, fighting, disturber, and prohibition. Any go player already has an intuitive knowledge about basic ko. The fighting rule dispenses with so called hot stones. The disturber rule restricts repeatedly cyclical play within one disturbing ko. The prohibition rule does the same for several ko positions on the board.


Definitions for Ko

ko mouth

A ko mouth consists of the marked board points in any of the following shapes, in any equivalent shape, in any equivalent shape with reversed colours, or in any such shape of which a part or parts - but not any marked board point - are cut off by at least one edge of the board. In any shape diagram not marked empty points may be of empty, black, or white colour as long as no illegal position arises.

Notes:

ko string

A ko string is a string in a ko mouth.

Notes:

ko stone

A ko stone is a stone of a ko string.

Note: A normal string shall be a string that is no ko string.

move-sequence

A move-sequence is a non-empty colour-alternating sequence of board plays or pass plays by both players.

ko stone move-sequence

A ko stone move-sequence is a move-sequence of board plays so that only ko stones are played.

ko coupling

Given a ko mouth and its adjacent strings. All of at least two ko mouths with all of the strings and none else being adjacent to each of the ko mouths have them as their ko coupling.

Notes:

ko position

If a ko mouth is adjacent to all strings of a ko coupling and not adjacent to any other string, then the ko position of the ko mouth is the union of the board points of all ko mouths that are adjacent to all strings of the ko coupling and not adjacent to any other string. If a ko mouth is not adjacent to all strings of a ko coupling or adjacent to another string, then the board points of the ko mouth are its ko position.

Note: Any ko position may remain on the board til the end of the game. Thus no theoretical problem can arise as to a way of dissolution of a ko position. Filling in is still possible. The Ing ko rules differently require each ko position to have a so called outcome.

Definitions of Ko Types

stable disturbing life

A ko position of a ko coupling is in a state of stable disturbing life if

Notes:

instable disturbing life

A ko position of a ko coupling is a state of instable disturbing life if the ko position is not in a state of stable disturbing life and a ko stone move in the ko position exists that transforms the ko position into a state of stable disturbing life.

Notes:

single disturbing life

A ko position which is not adjacent to all strings of a ko coupling or is adjacent to another string is a single disturbing life if - with each adjacent string to the ko position having as an assumption at least one breath not in the ko mouth - on it a ko stone move-sequence of infinite length could not be played or if it is a ko mouth that consists of 4 board points in a row and has not had on it two ko strings after a move.

Notes:

disturbing life

A ko position that is in one of the states stable disturbing life or instable disturbing life or that is a single disturbing life is a disturbing life.

stable disturbing death

A ko position of a ko coupling is a state of stable disturbing death if

Notes:

instable disturbing death

A ko position of a ko coupling is a state of instable disturbing death if

Note: The strings of the ko coupling, that have the breaths of the ko position, are called dead in disturbing death. They temporarily seem to escape removal.

single disturbing death

A ko position consisting of exactly two board points is a single disturbing death if in the cases of a ko stone of one respectively the other colour in the ko mouth all adjacent strings to the ko stone could have after a move of the player of these strings at least two breaths respectively at most one breath provided that the move would neither capture the ko stone nor reduce the breaths of at least one of these strings.

Notes:

disturbing death

A ko position is a disturbing death if it is a single disturbing death or in one of the states stable disturbing death or instable disturbing death.

disturbing ko

Disturbing life or disturbing death.

Note: A distinction of disturbing life and disturbing death generally ensures in a disturbing life ko threats for both players and in a disturbing death a problem-free removal of so called dead strings.

fighting ko

A fighting ko is a ko position that is no disturbing ko.

Notes:

disturbing a disturbing ko

A player is disturbing a disturbing ko if

Notes:

Rules

Basic Ko

A single ko stone that has captured a single ko stone may not be recaptured immediately.

Note: A recapture must be preceded by at least one board play or pass play of at least one player.

Fighting

If in a fighting ko a ko stone is played, then the opponent's next move may not play a ko stone in it.

Notes:

Disturber

During a ko stone move-sequence in a disturbing ko a player becomes the disturber of the disturbing ko by disturbing it first. As soon as the ko position of the disturbing ko with the stones on it has been repeated since the moment just before the occurance of the current disturber, he is not allowed to disturb the disturbing ko. With the end of the ko stone move-sequence in the disturbing ko a disturber ceases to exist. If the disturber is not allowed to disturb the disturbing ko and the ko stone move-sequence in the disturbing ko continues and leads to a disturbing move by the other player, then the disturber ceases to exist and the other player becomes the disturber.

Notes:

Prohibition

From all board positions with the same set of board points of all ko positions and with the same configuration of stones on the board without the set each player may only once play a ko stone in each fighting ko, become disturber of each disturbing ko, or otherwise play a stone on each board point. As an exception for all such board positions the first played ko stone in a fighting ko is ignored.

Notes:


Acknowledgement

I would like to thank all persons who have verbally or in writing discussed go rules. Without their - including many of you - great efforts this page would not have been possible.

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