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Sending Two Returning One
Keywords: Rules
An aspect of territory scoring is that one player may have a way to prolong the game while losing points. (See example on the Tsumego From Games 21 page.) Under area scoring a play inside territory to prevent this would cost nothing, right at the end of the game. That isn't the case under territory scoring; it may be practical to give back one point eventually.
Charles I was thinking of something like this.
White at a is a threat (to make seki) so that Black must capture two; White then can recapture one to repeat the board position. If Black eventually plays b that prevents the repetition.
W 3 at the circled stone.
Now Black can play at 4 with no net loss, regardless of scoring method.
There may be no such play, as in the case just cited and also in the example on the superko page. Then in principle under territory scoring one allows the opponent to do it 100 times (say) and then passes instead of continuing round the cycle, allowing the opponent to take a few stones. Under a superko rule such positions cannot be repeated indefinitely. Side note: The phrase sending two returning one is a direct translation of 打二还一, which describes the sequence below and is used to differentiate it from ko when teaching Go rules to beginners. --unkx80
White 2 is a legal move even if played immediately after Black 1. This is a copy of the living page "Sending Two Returning One" at Sensei's Library. ![]() |