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Molasses Ko
Path: SecondCourseOnKo   · Prev: RogueKo   · Next: PinwheelKo
  Difficulty: Advanced   Keywords: Life & Death, Ko, Shape, Rules

The Molasses Ko is a strange construct, which behaves differently under different rules and might slow the game down to 20% of the normal pace by making it mandatory to exchange four moves after every regular move.

[Diagram]
Molasses ko (Black to play)

Assuming that there are no ko threats big enough, this situation will repeat as long as there are valid moves on the board.

What is a ko threat? Depending on your definition, every tenuki or pass could be called a ko threat[1]. More generally, one speaks of restriction threats. If passes are involved or threatened to be involved, then one calls the particular restriction fights pass fights. --RobertJasiek

After the moves a-b-c-d the original situation is reversed (next diagram):

[Diagram]
Black plays elsewhere

It's still Black's turn, and he uses it to make an ordinary move somewhere else. If that move was not a huge ko threat, White must reset the position (next diagram):


[Diagram]
White continues (5 elsewhere)

After 1 to 4 it's White's turn to move, and she will play elsewhere. (for example, White could answer the move Black made after a-b-c-d in the first diagram.)

Now the local situation is exactly the same as it was in the first diagram, and the cycle repeats.



Omitting the exchange

Both players must make this exchange after every move played elsewhere, or his/her stones are captured.

[Diagram]
Black omits the exchange after White played elsewhere and loses his stones

If Black omits the exchange, White can play 1. Now the situation is a real ko, and as was stated above, there are no ko threats big enough, so the black stones are lost.



Status?

What is the status of the groups involved in a molasses ko? I really have no idea whatsoever :-) My first guess would be seki, since neither player can capture the other.

On the other hand, it could be a no-result, since after either of the players passes, the other will take this ko. This will of course depend on the wording of the ko rules used.

If superko rules are used, the game will be decided by "who has most valid moves" (since you always have to play elsewhere or lose). Number of valid moves can be counted by adding up every distinct eye, and then subtracting 2 for every separate group.

Bill: It's more complicated than that. See No Pass Go.

In this situation, the effect of komi is nullified, since the counting system reverts to stone counting scoring. :-)

Go figure :-)


[1] Bill Spight: I see Robert's point. If a play removes the restriction against taking a ko, then it carries the threat to take the ko. In that case, any board play, and, according to some rules, any pass is a ko threat. However, such a definition is so broad as to be meaningless. The threat in a ko threat is to make a profit somewhere other than the ko if the opponent does not respond, not the threat to take the ko.
Sometimes certain plays which are not, properly speaking, ko threats, perform a function of a ko threat. I call these virtual, or tertiary ko threats. For more, see Komonster.


"molasses ko", indeed! tee-hee! you guys are silly. nice one. -liquidkat



Path: SecondCourseOnKo   · Prev: RogueKo   · Next: PinwheelKo
This is a copy of the living page "Molasses Ko" at Sensei's Library.
(OC) 2004 the Authors, published under the OpenContent License V1.0.