1998-12-01 last update, 1996-06-15 first day, Robert Jasiek

Comparison of Ko Rules

Three sets of ko rules are compared:
1 - Japanese Nihon Kiin 1989,
2 - Ing 1991,
3 - Tromp-Taylor 1996.

Their main features are:
1 - generally only single ko stones possible,
2 - two types of ko: fighting ko and disturbing ko,
3 - super-ko rule.

History:

• 1 - The Japanese ko rules have only evolved slightly. 1949 the oral rules were written down with minor changes. 1989 a set of rules has been created, that is more precisely and appears to be rather logical. It succeeded in absorbing all precedents.
• 2 - In the second half of this century Taiwan introduced its own rules, that included a super-ko rule. A change to a distinction of ko types was meant to improve the rules.
• 3 - Maybe the Ikeda rules could be regarded as ancestor of modern sets of rules like New Zealand and AGA rules. Tromp-Taylor rules are evolved from New Zealand rules.

Rules:

1 Japanese:

They consist of 3 ko rules:

• a) "A shape in which the players can alternatively capture and recapture one opposing stone is called a 'ko'. A player whose stone has been captured in a ko cannot recapture in that ko on the next move." (single ko stone rule)
• b) "When the same whole board position is repeated during a game, if the players agree, the game ends without result." (other repeatition than single ko stone rule, e. g. triple ko)
• c) "In the confirmation of life and death after the game stops (...), recapturing in the same ko is prohibited. A player whose stone has been captured in a ko may, however, capture in that ko again after passing once for that particular ko capture." (confirmation-phase pass for recapture ko rule; valid for determining life and death in confirmation phase and for determining result)

2 Ing:

There are fighting ko and disturbing ko. Life and death are not settled or settled, respectively. In fighting ko immediate recapture of any 'hot' ko stone is prohibited. In disturbing ko it is allowed to play through a cycle until the ko position is repeated for the first time.

In practice 3 cases occur:

• a) fighting ko: e. g. - single ko stone, - eternal life, - triple ko (3 ko breaths).
• b) disturbing life: e. g. - double ko seki, - quadrupel ko, - quintupel ko. Each side has at least two eye breaths. The ko breaths are paired and balanced. (As soon as there are enough eyes this is always the case.)
• c) disturbing death: The strings of one side cannot get two real breaths. They are dead and can be taken off the board before the end of the game.

3 Tromp-Taylor:

"A turn is (...) a move that does not repeat a position."

Thus repetition of a whole board position is forbidden.

Evaluation:

1 Japanese:

Advantages:

• + Japanese tradition is preserved
• + games without result are possible, so that memory of Nobunaga's death is preserved
• + game records are not blotted by superfluous encores

Disadvantages:

• - 3 ko rules are necessary
• - detailed commentary on the rules is required
• - proof of logical correctness cannot be given
• - tradition is overemphasized
• - games may end without result and are to be replayed
• - no beginner understands the end of a game

2 Ing:

Advantages:

• + the rules reflect high level go skill
• + no games without result
• + long cyclical sequences occur less often

Disadvantages:

• - high level go skill is needed to understand the rules
• - positions might occur that cannot be analized by the rules within resonable time
• - an important purpose of the rules, i. e. to avoid all long cyclical sequences, is not achieved
• - an important purpose of the rules, i. e. to allow maximal variety, is prohibited by rules of disturbing ko
• - an important purpose of the rules, i. e. no special rulings, is avoided by 2 ko types
• - 2 basic types of ko are necessary
• - many terms must be introduced
• - detailed commentary on the rules is required
• - the rules lack of definitions, that could be mathematically treated
• - the rules are incomplete
• - the rules cannot be learned easily

3 Tromp-Taylor

Advantages:

• + simple and easy to understand
• + logically correct

Disadvantages:

• - long cyclical sequences might occur

Conclusions:

1 Japanese:

They favour tradition instead of simplicity and logic.

2 Ing:

They favour reflection of go skill instead of simplicity and logic.

3 Tromp-Taylor:

They are simple and logical. They do not have serious disadvantages.

Summary:

Rules ought to be simple and logical. The only ko rule to satisfy these features is the super-ko rule. Its only disadvantage is the possibilty of long cyclical sequences in case of several ko stones. Either one forbids them by ruling "no outcome", or one leaves them for go skill.

Afterwords:

Tradition has produced many special board positions with desires for their treatment. Rules were constructed so as to consider those desires. The super-ko rule may give different results from traditional rules. However, its simplicity and logic destinates it to be part of a standard set of rules for the whole world. It can be easily used by computers as well.