Simplified Core Rules of Play

"core rules of play" describe legal strategy during each game and definition of its winner. Everything else is called "tournament rules". In particular, compensation, counting procedures, or time management belong to tournament rules. Here we do not confuse the simplified core rules by already adding any such tournament extensions.

The common simplified rules are used by every simplified ruleset.

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Common Simplified Rules

General

• Two players play the game with stones on a board.
• One player uses black stones, the other white.
• The board is a grid of 19 horizontal and 19 vertical lines forming 361 intersections.
• Two intersections are adjacent if they have a line but no intersection between them.
• Two intersections with either black, white, or no stones on them are connected if they are adjacent or if there is a chain of adjacent intersections of their type between them.
• A region consists of an intersection and any intersections connected to it.

Move

• A move is either a play of an own stone on an empty intersection, or a pass.
• A play causing stones' regions to be without any adjacent empty intersections removes those stones. Removing opposing regions takes precedence over removing own regions.

Phases - Common Rules

• The game consists of the following phases in order: 1) alternation, 2) agreement removals, 3) disagreement alternation, 4) winning.
• In the phase alternation the Black player starts alternation.
• In the phase alternation the players move alternately.
• The phase alternation ends with a succession of two passes.
• During the phase agreement removals the players may either agree or disagree on removal of stones.
• If during the phase agreement removals the players agree on removal of stones, then those stones are removed, then the phase disagreement alternation is skipped, and then the phase winning follows.
• The winner is given during the phase winning due to the favourable score difference of the Black player and the White player.

No Recreation

• A play of a stone may not recreate any earlier distribution of black and white stones on the board. This refers to the distribution just after the play and any consequent removals.

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Simplified Ing / New Zealand Rules

Phases

• The phases alternation, agreement removals, and disagreement alternation are a contest of skill. The phase winning is not a contest of skill.
• If during the phase agreement removals the players disagree on removal of stones, then none are removed, then the phase agreement removals ends, then the phase disagreement alternation continues from the phase alternation, then the phase disagreement alternation ends with a succession of two passes, and then the phase winning starts.

Score

• Each player's score is the sum of numbers of intersections a) with his stones on and b) of empty regions only adjacent to intersections with his stones on.

Simplified Chinese Rules

No Suicide

• A play is prohibited if it would require removal of an own region.

Phases

• The phases alternation, agreement removals, and disagreement alternation are a contest of skill. The phase winning is not a contest of skill.
• If during the phase agreement removals the players disagree on removal of stones, then none are removed, then the phase agreement removals ends, then the phase disagreement alternation continues from the phase alternation, then the phase disagreement alternation ends with a succession of two passes, and then the phase winning starts.

Score

• Each player's score is the sum of numbers of intersections a) with his stones on and b) of empty regions only adjacent to intersections with his stones on.

Simplified Japanese / Korean Rules

No Suicide

• A play is prohibited if it would require removal of an own region.

Phases

• The phases alternation and agreement removals are a contest of skill. The phase disagreement alternation and winning are not a contest of skill.
• If during the phase agreement removals the players disagree on removal of stones, then during the phase disagreement alternation all those stones are removed from the board that have not but could have been removed during wise continued alternation during the phase alternation, then the phase winning follows.
• During the phase disagreement alternation imagined wise alternation is done hypothetically only and treated as if it would be cost-free to play more or fewer stones than the opponent.

Exceptions

• Seki is a state of an intersection called so wisely. During the phase disagreement alternation exceptionally stones from intersections in seki are not removed. During the phase winning exceptionally intersections in seki do not belong to a player's score.
• During the phase disagreement alternation exceptionally no recreation of the distribution of black and white stones on the board is also treated wisely to avoid any usage of so called ko threats.

Score

• Stones removed during the phases alternation, agreement removals, or disagreement alternation are kept as prisoners.
• Each player's score is the sum of numbers of a) intersections of empty regions only adjacent to intersections with his stones on and b) prisoners of opposing colour.

Simplified AGA / French Rules

No Suicide

• A play is prohibited if it would require removal of an own region.

Phases

• The phases alternation, agreement removals, and disagreement alternation are a contest of skill. The phase winning is not a contest of skill.
• If during the phase agreement removals the players disagree on removal of stones, then none are removed, then the phase agreement removals ends, then the phase disagreement alternation continues from the phase alternation, then the phase disagreement alternation ends with a succession of two passes, and then the phase winning starts.

Score

• Exceptionally the phase alternation ends with an extra pass of the White player if he has not passed as the last player.
• Stones removed during the phases alternation, agreement removals, or disagreement alternation are kept as prisoners.
• Each time a player passes he adds an own stone to the prisoners.
• Each player's score is given as one of the following sums of numbers: 1) Intersections a) with his stones on and b) of empty regions only adjacent to intersections with his stones on. 2) a) Intersections of empty regions only adjacent to intersections with his stones on and b) prisoners of opposing colour.

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Commentary

• Strategically the game of Go is very similar under all rulesets.
• The practical strategic difference between suicide or no suicide is too rare to be relevant.
• The practical strategic differences between a current ruleset and its simplification are rare.
• The exceptions with the greatest practical relevance are all found in current Japanese / Korean rulesets: a) no value of one excess dame intersection in an even game with one odd seki and 5.5 or 7.5 compensation points, b) asymmetrical sekis, c) long cycles. All these are scarcely or even rarely of any significant importance for winning the game.

Simplified Ing / New Zealand Rules

• Suicide is allowed.
• Ko is simplified as positional superko. Neither of the two passes ending the phase alternation can be ko threat for continued alternation in the phase disagreement alternation because the superko rule is positional and because the same player can play next on the board that could play next on the board just before the two passes.
• Any disputes about removals can be played out as a competition of skill. Therefore a referee cannot override the players' will to do so if at least one of them likes.

Simplified Chinese Rules

• Suicide is prohibited.
• Ko is simplified as positional superko. Neither of the two passes ending the phase alternation can be ko threat for continued alternation in the phase disagreement removals because the superko rule is positional and because the same player can play next on the board that could play next on the board just before the two passes.
• Any disputes about removals can be played out as a competition of skill. Therefore a referee cannot override the players' will to do so if at least one of them likes.

Simplified Japanese / Korean Rules

• Suicide is prohibited.
• Sekis only rarely make a difference when they are asymmetrical.
• Cycles longer than two moves do not have any exceptional treatment because such would make a difference only rarely.
• There is no confirmation phase. The players are supposed to occupy dame, teire, and intersections related to removals from seki already during the phase alternation.
• The phase agreement removals is not part of original Japanese / Korean rules but included for consistency with other rulesets and frequent informal practice among non-Asian amateurs.
• Since different numbers of plays are not compensated, during the phase removals plays must be assumed cost-free.
• Theoretically it would be possible but extremely ugly and an overkill to provide greater precision for seki or for treatment of no recreation during the phase removals.

Simplified AGA / French Rules

• Suicide is prohibited.
• Ko is simplified as positional superko. Neither of the two passes ending the phase alternation can be ko threat for continued alternation in the phase disagreement removals because the superko rule is positional and because the same player can play next on the board that could play next on the board just before the two passes.
• Any disputes about removals can be played out as a competition of skill. Therefore a referee cannot override the players' will to do so if at least one of them likes.
• The combination of letting the White player pass last and of spending one prisoner per pass permits equivalence of two ways of defining the winner. Strategically the game behaves as if the winner is given due to stones on the board plus empty regions.