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Strange Sekis
The analysis of the following strange positions needs some knowledge: perhaps you first read about ordinary sekis and get right the number of liberties in a big eye. 1
For a first challenge, try to solve the following position (it is not a seki ; you will find a commentary in
2If you succeeded, this is harder: what is the difference between these two positions?
Robert Pauli: Let's fit'em on 10x4 (less scary ;-):
3Are you still there? Now for something really new: a never seen before type of seki (and it is possible to prove that this is essentially the only one of this type, so you should not really expect to see it in a game sometime - you are probably seeing here a glimpse of go in the 21,0000th century :-))
Robert Pauli: Let's fit it on a 10x10 (9x9 seems to small):
4Now, three 4-group sekis...except for the last one ! (but then, why is the second one a seki?) I will let you think about it for a few days ...
Robert Pauli: Would you call this one seki, Denis?
f3etoiles Mmm. I did count, but might be wrong, as I find White still win a point by breaking the seki (chinese count, at least the odd result is not so odd :-} > Anyway, if you thought it balanced (no difference in point) I would call it a non-terminal seki, at least .... Robert Pauli: Under territory scoring White gains zero by sacrificing his left side - he ends with 10 points territory and 12 captives, just like Black - but since he loses sente, one might still call it seki.
Bill: By Spight rules with territory scoring this is terminal, but will be played out in the encore for a White win (-1). By 5Now for something really strange : an asymetrical 3-group seki. I can hardly believe it (especially as it was missed for so long), but I cannot find my mistake . . .
To please Robert Pauli, here is a 6x6 version :
Robert Pauli: Thanks, Denis, but this one is smaller, plainer, and more balanced (too bad not one black stone can be reversed):
f3etoiles No, it is correct (well, as far as 4x8 games go), as the last moves could have been, for instance
Robert Pauli: Yes, of course, but balancing without captives is what I like (even if that should lead to an "ugly" rectangular board :-). BTW, the one with the T enables a sacrifice! White can trade his small eye to bring life to his big eye:
On your 6x6 this costs White seven points (territory scoring), on my 4x8 three points, however, some (bad) ruleset might reward White's option somehow in post-end analysis . . . Couldn't avoid the T on the 6x6 (square may not be in the corner, OC). My best try:
Move whatever you feel to the discussion page. 6Did I find something new at last ? Judge for yourself . . . But I am now almost sure that this is a complete seki, with 4 (count them, four) mutual liberties between two groups . . .
% RP: Should have been Solution6.
Robert Pauli: Pleased (. . . and not so sure :-) You stressed "four" liberties in the center, Denis, but what's the disadvantage of filling one but the last? f3etoiles Alas, I discovered a few days later that I was completely wrong. What is the real result of this position (it is not a seki)? And, when you will have solved it, what is the Japanese ruling of the following position ? (Hint: there is a strong connection between both :-))
Robert Pauli: Where's the trick, Denis? White can capture the black one-eye group, and Black can capture the white one-eye group - no matter who starts. For whatever reason they didn't, however. Rubyflame: No matter who starts? It sure seems to me that whoever moves first wins. Robert Pauli: Hmm . . .
Now Black's left chain has (four is) five liberties, but White too (at least), plus sente. Rubyflame: No, white's right chain has only two liberties now. When it is captured, the black group on the left is saved. Your diagram is not equivalent to the one above.
Now White's right chain (still) has two liberties, but Black has four (at least). Rubyflame: Here, white should have played at a (at least in the original diagram).
Robert Pauli: Outch, my simplification indeed is not equivalent to the original. You're completely right, Rubyflame. The one-eye groups are neighbors - who starts, gets it all. A valid shrink might be:
Under Japanese 1989 rules all stones would be dead, but since they're not in territory (in my shrink), to no avail: zero to each. If alive stones of both colors are surrounding, it would be a (technical) seki. If just one color surrounds, my personal interpretation is to have it territory of that color, own dead stones already filled in. Author: f3etoiles
See a Matti? Siivola This is a copy of the living page "Strange Sekis" at Sensei's Library. ![]() |