Triple Ko/ Discussion

Sub-page of TripleKo
[Diagram]

An example of triple ko

About superko:

Specifically, there is the so-called positional superko rule, in which case it is the position which cannot be repeated, or the situational superko rule, in which case it is not just the position, but also the situation (i.e. the player to play) which cannot be repeated.

In the a/b/c ko example above, the cycle length is six under both PSK and SSK rule. White is dead because she will eventually run out of ko threats and Black doesn't need any. (I (anonymous) needed pencil and paper to work this out, so I think the superko rules are impractical without the aid of a computer.)

Bill: Robert Jasiek's previous comment still applies: Something wrong here.

Some Ko-rules allow one repetition, but not more.

The superko rule also has other implications; normally the board position repeats after a few moves (in the above example, after six moves). However, the sequences of moves, which produce the same board position, can be large and involve captures by both sides. As long as both parties are unwilling to play another line of play (they both consider the play which leads to the 'superko' optimal) then the superko situation will arise.

It should be noted that, under current Japanese rules, situations which would be prohibited by a superko rule will lead to a no-result (not jigo), and not to a loss for the player who plays the move.

(Actually, under Japanese rules the no-result is pronounced only upon agreement by the players. --Bob Myers)

However, the positions are very rare. I have never seen one in real life. When they do occur, they are normally talked about a lot - because they are so rare. If either player is leading enough to discard a group here then the game may be continued. Otherwise, if the winner is determined by who kills here, they have to fight three ko. Black captures at a, White at b, Black at c and then White has to capture at a if rules allow a return to the initial position.

-- HolIgor

For more information about the various rulesets in general and ko rules in particular, take a look at Robert Jasiek's [ext] homepage

-- Morten Pahle

Uhhh.... Just to let you guys know... 'b' isn't a ko... If white plays at b, it captures that whole black group. -God Ginrai

Bill: Err. White would win the triple ko, that's all.

Later: Somebody altered the diagram caption to say that Black was to play. That is not necessary. It is still a triple ko, regardless of who has the move. The same is true for a simple, direct ko. One player with the move can win the ko, the other player can take the ko.

We could even be in the middle of a superko fight. White might have taken the triple ko, capturing a stone at a, and Black might have just played a ko threat.


This is a copy of the living page "Triple Ko/ Discussion" at Sensei's Library.
(OC) 2007 the Authors, published under the OpenContent License V1.0.
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