Rules Beast 1 (version 42)

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John Tromp: On small boards the superko rule has peculiar consequences as exemplified in this 6x6 game:


Here, White to move had better connect in the lower left, else Black can exploit the superko rule to capture a white group. Hint: Black aims to make it illegal for White to capture in the top-right a second time. (Play below.)

I don't see these strange consequences as an indication that there's something wrong with the superko rule. In fact it seems to fit right in with the other simply-stated Go rules that yield a game so rich in strategy and subtleties.

Charles Matthews So this page should reference sending two, returning one.

I think the final paragraph is a partisan statement, by the way. If various organisations of standing in the go world have been persuaded to adopt superko, was it really to introduce more 'subtleties', or because it was represented as suppressing others?

Bill: I created this page using John's example in Superko. As one author of an elegant rule set, John has an informed opinion. I felt that it was fair to retain it here.

I am pretty much in agreement with you, Charles. The behavior of this board under most rules sets with a superko rule seems to me to be an unintended consequence.

White passes (i)  

W1 = pass


OTF: White passes (ii)  

W9 = pass

Under most superko rules (e. g., AGA, New Zealand, Lasker-Maas, Tromp-Taylor), White cannot now take B8 and B10, since that would repeat the situation after W7.

Christos Dimitrakakis This problem does not occur under a situational superko, since in one occasion it is black who is to play, while on the other it is the white player whose turn it is to play. Thus, while there is a repeated position, there can be no cycle.

Bill: The banned position is the one after W7, which White would repeat on move 11, recreating the same situation, with Black to play. So it does occur under a situational superko rule.

Under Spight rules White can take the stones, since White's pass (W9) lifted any ko or superko ban.

Under Kee Rules:

Initial board position  
Black sending two (again)  

Black captures the white stone by B1. W2 is a normal pass play and Black sends two again by B3.

W4 triggers a cycle  

W4 triggers a cycle, but Black is prohibited from playing in the remainder of the game because White has a normal pass play within the cycle but Black has not. White wins by playing the remainder of the game by himself alone.

Robert Pauli: Let's see how LJRG perform.

Cycles, besides ko, are not prohibited by LJRG. Instead, one may (if passing wouldn't end) remove the cycle.

If White passes and Black disturbs, the situation after W11 is similar to the one after W7 (with no history, trees growing out of them are identical). LJRG now allows Black to

  • clear the cycle arena (top three intersections of the right-most column) -- thereby earning one white captive and prohibiting any further play in it -- and
  • do a move.

Since there is nothing worth continuing, Black will skip the second part, White will pass, and Black will pass too, ending the game (ultimately): W+5 (no part of the board is controled, and there are two white and seven black captives).

Since the whole mess doesn't pay, Black will rather pass after White did initially: tie (neither any control nor any captives).

Thus, White should have captured the black loner in the seki instead to pass initially: W+1.


Osh?: maybe white is better to bring everything to Seki? If there was a komi...

By W1 it is seki in left below side. If B2 eats...


White cuts then black captures this white stone, but after that white takes three black stones and...



Unfortunately this is only possible if this position were previously unavailable. Not so clear.



Black cannot go here, else the white group is alive. So it is unreasonable for black to reply in left below side



So if B2 will threat to capture big white group in the right above side - W3 kills two black stones and black cannot repeat a position before.

After all in a case that there was a komi, white wins. Could it be?

Rules Beast 1 (version 42) last edited by Osh on May 25, 2018 - 04:19
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