Ko Fight - Complex Situations Involving ko

Complex Situations Involving ko

One curiosity is the existence of multiple kos on the same board at the same time. A double ko is a situation when two kos are potentially being fought, simultaneously and affecting the same local position. Such positions are uncommon, but do sometimes arise in actual play, affecting life and death or connection issues. Two kos cannot actually form a large loop.

A triple ko is when three kos are being fought simultaneously. In this case a long loop, of period six plays, can occur, not being ruled out by the ko rule: it is possible for the two players to continually take and retake the three kos in a fixed cyclic order. If both players judge this to be the best line of play, then the game could, theoretically, continue forever. When there are three kos on the board, it does not follow that there will be a triple ko: as long as one player can concede two out of three and still be ahead, there is no reason for the loop to persist; and normally that is true. When such a position does occur, the game is called off and the opponents begin a new game. However, this only occurs with the so-called "basic ko rule" that one cannot recapture immediately.

There are other, stronger ko rules, the main class being superko, where repeating positions of any cycle length are impossible: see Rules of Go. Such events, however, are extremely uncommon and many go players may play their whole lives without restarting a game due to a triple ko.

Such rule issues, therefore, are more a matter of principle, although considerable attention has been devoted to them: see Sensei's Library's overview.