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group tax
Keywords: Rules
The rules concept, for go scoring, of deducting two points (the two necessary eye points) from each of the players, for each of their live groups at the end of the game. It was used in China before modern area scoring as a convenience in stone counting. You subtract the eyes needed for life from the area, since the player cannot afford to fill those points. What happens to a seki like this one?
The surrounding groups have 11 points each, but B has two groups to W's one, so excluding the seki the score is W 9, B 7 with group tax. W wins.
Bill: If the group tax is used with area scoring, as is was in recent history, then each of the White groups in the seki are taxed one point, since they each need an eye to live. The group tax provides a way to do stone counting. White then gets 25 - 2 = 23 points for the independently alive group plus 5 - 1 = 4 plus 7 - 1 = 6 points for the seki groups, for a total of 33 points. Black gets 15 - 2 = 13 plus 14 - 2 = 12 points for his independently alive groups, plus 2 points for his seki group, for a total of 27 points. There is speculation that ancient go used territory scoring with a group tax. If so, that may be a historical reason[1] why eyes in seki do not count in Japanese scoring.
To give a picture to what Bill is saying: This seems to be the way the group tax takes effect. Now we just count the black and white stones once no more plays can be made, and there's the score. B: 27. W: 33.
[1] Robert Pauli:
Each side has played 14 stones. Black passes. White adds two further stones and wins by two, just as if White had count his two false eyes under territory scoring. This is a copy of the living page "group tax" at Sensei's Library. ![]() |