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Sending two, returning one
Difficulty: Beginner Keywords: Tactics, Rules
The phrase sending two returning one is a direct translation of the Chinese phrase 打二还一, which describes the sequence below and is used to differentiate it from ko when teaching Go rules to beginners. --unkx80
An aspect of territory scoring is that one player may have a related 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. Actually it's area scoring that has a problem with "sending two, returning one".
Without some super ko rule, this 4x3 game wouldn't end:
Under territory scoring, on the other hand, White (leading by, say, 1 prisoner) would simply give up the whole board at the moment she piled up enough black prisoners - 26, I guess. :-) Harry Wang: Actually, in GO, endless attack by black is NOT allowed. The game ends with white winning over black.
In case suicide is an option and Black commits it (clearing the whole board), the game will continue as shown, forcing Black to pass with
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.
Now Black can play at 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. This is a copy of the living page "Sending two, returning one" at Sensei's Library. ![]() |