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Nit: Go's game state isn't just defined by the board state and whose turn it is, but also by the history of all prior board states (which would still be public

• pmontra 9y ago
  Tewari is a common technique for analyzing go positions. You alter the order of the moves to get to the same final position and, as all the stones (the pieces) are the same, if one sequence ends with a silly move of a player, but there are no silly moves of the other player in any sequence, then the first player made a mistake. This means that the history of the game is pretty much irrelevant. Usually only the last two moves are important because you can't recapture a stone and get to the very same position as two moves before. It's called the ko rule (another unfortunate word clash with English.) There is also triple ko (three linked kos), which requires to remember more moves back, like for repeated positions in chess. A go game with a triple ko has no result: there is no draw so the game must be played again if in a tournament. It's very rare.
  • mrob 9y ago
    >A go game with a triple ko has no result True under Japanese rules. Chinese rules at least theoretically use a superko rule. But many comments online say in practice the game is voided under Chinese rules too. http://senseis.xmp.net/?Superko http://senseis.xmp.net/?Superko