American Go E-Journal

Triple Ko in Tiger’s Mouth Tourney

Monday May 27, 2013

An interesting triple ko came up in the most recent Tiger’s Mouth prize tourney.  The tourneys are run every month, and are open to youth in the US and Canada. Handicapped, and with prizes in double-digit kyu, single-digit kyu, and dan sections, the tourneys provide challenging games for players of all levels, with prizes courtesy of the AGF.  The triple ko came up in a six stone game between Narnian 12k, and Gocookrice 18k, and can be seen in the attached game record. The ruleset was Japanese, which technically means the game should be no result. The players asked the TD to make a ruling, he decided it was a seki, and gave the win to white on territory.  How would the triple ko have been resolved in other rule sets?  The E-J asked Yilun Yang 7p to weigh in with Chinese rules: “If both players keep taking the ko in this situation, it seems the game should be no-result. Black has to keep capturing,  otherwise black loses. Unless one side gives up the ko battle, no one can win, and neither player can give up the ko in this game.”

AGA rules resolve the issue by making full board repetition illegal, which turns this situation into what is called “Super Ko“. AGA Rules Coordinator Terry Benson says: “The main point of AGA rules is that the players have to figure and play it out – not the ref – and we have no null games. A triple ko is going to prohibit the 6th move. So who starts matters. Thus finding a ko threat on move 6 which the opponent answers, would reset the triple ko with the other player to start. I think Ing rules would be the same. This is a fighting ko.” See move 257 to illustrate the options.

E-J Games Editor Myron Souris has a succinct analysis for this situation: “according to AGA rules Black wins the triple ko, no matter who plays first.  If Black takes 1st, then 6 moves later White would be forbidden from repeating the position from just before Black’s 1st move.  So White dies.  And White taking the triple ko 1st is useless, because Black is alive in double ko. With the AGA rules, Terry and the rules committee devised a truly beautiful ruleset:  simple, rigorous, and sensible. Numerous people have unfairly criticized the AGA ruleset for being to difficult to apply to these multiple ko situations, e.g., ‘Knowing when a previous board position repeats is too difficult.’  Terry’s analysis exposes that misconception for this game.  A few years ago, I found about a dozen pro games (the latest is the infamous 2012 Gu Li vs. Lee Sedol game) ending in triple and quadruple ko, all of which even I could apply the AGA rules to resolve who would have won without too much work. Yes, some contrived multiple ko situations can be extremely difficult to analyze for who wins; however, those situations don’t seem to appear in real games, and in any event, the AGA allows the players to play out the situation themselves.” To sign up for the next Tiger’s Mouth Tourney, on June 15th, click here. -Paul Barchilon, E-J Youth Editor