Group Tax/ Discussion

Sub-page of GroupTax

moved from stone scoring

(What follows is a discussion of passing and the two point 'tax' vis-a-vis the ancient rules. Reading through to the end reaches a conclusion, and so this section still needs a WikiMasterEdit.

Stone scoring went out of general use in China in the early part of the 20th century, presumably because the strong players were learning from Japanese sources. An effect of the old Chinese rules was not to score 2 eye spaces per independently living group.

In the ancient rules, passing is not allowed -- this translates to the "don't count the 2 spaces for eyes" rule -- also known as the [two-point group tax|group tax]. John Fairbairn could probably give you more details about this history.

Passing disallowed?  

I don't think the two point 'tax' is equivalent to disallowing passing (if you mean that you lose if you have no move other than passing). In the diagram shown, White has three points after tax, while Black has four. But I think White can win the no-pass game, whoever starts.

''There is no group tax in this diagram. What you are seeing, is that this kind of game is decided by number of distinct eyes, not by the size of the eyes. This kind of situation can occur when a MolassesKo is on the board --Bass''

In the position above, white has played 20 stones (that we can see, perhaps more if there have been captures) and black has played only eleven (again, 11 that we can see). Also notice that W occupies much more area than black. While black has more "Japanese" territory in the diagram above he white must have at least 9 prisoners (since black is not allowed to pass). By either Chinese area scoring or Japanese territory scoring white is way ahead and should win so saying that the diagram above proves that "2 point group tax" does not equal "no passing allowed" is false.

Of course black and white both have the same number of groups above (1 each) so any possible tax cancels out. A proper counter example to my claim would probably have an uneven number of black and white groups.


Jonathan Cano Robert Jasiek has replaced some "counting" by


13x13 version  

No. Consider this version on a 13x13 board. Each player has two groups and 77 stones. White has three points after tax. Black has four. Black to play, White wins.

Excellent! I had a suspicion I was wrong and your last diagram proves it.

Ah, I think I remember a modification to the ancient rules that do properly implement the 2 point group tax. Here it is:

  • both players must move. The first player who can not move loses.
  • A move consists of placing a stone on the board or returning a captured stone to your opponent.

I believe these modified ancient rules give the desired 2-point group tax when used for your diagram above.

for example, if black has to move next then he should win by 1 move.

black wins with modified ancient rules.  
black wins with modified ancient rules (cont).  

Black 7: return the captured stone white 2.

When black plays 11 at A white has lost.

If we start the problem with white moving first then black wins by 2 points. (this is left as an exercise)

Thanks for helping remember the proper rules for implementing the 2- point group tax.

Jonathan Cano

White wins.  

This is group tax in effect. -- Bass

W to play  

Robert Pauli: You could have done it simpler, Bass.

White wins under no-pass rules, but area scoring leads to a tie.

Mystery Go Player: I agree with what Bass has stated here and not much else. When each group is taxed 2 points, it means that multiple groups of one colour can't compete with same sized point scoring with only one group. When thinking about Chinese counting rules (and the importance of stones played), this makes sense. Although some people dislike Chinese rules for the way seki is scored, and as such, this rule adds complications. If we understand a seki situation as one Black VS one White group where neither is able to make outright life, we can simply shrug off the 2 point group tax because both sides are penalized once -- making it "equal". However, please consider the example below:

Black is better off with Group Tax  

It can be argued that since White has two unkillable "groups" then White needs to pay the tax twice compared to Black paying it once for those two unkillable stones.

Bill: In Stone Counting there is no group tax per se. Group tax is just a manner of speaking, a way to talk about the difference between types of scoring. In this diagram White has two fewer points by stone counting than by modern area scoring. The fact that a group tax of two points per group gives the right answer is coincidental.

Group Tax/ Discussion last edited by Bill on January 23, 2009 - 18:15
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