Strange Sekis

Either-or death  

Robert Pauli: Without wart and colours switched, that's the great life-and-death example 4 of the Japanese 1989 rules, and BTW, White wouldn't mind if Black started ;-)

Solution

Either-or-dies seki  

Robert Pauli: This one is seki (suicide banned).

Similar position 2  

Solution

Robert Pauli: Let's fit'em on 10×4 (less scary ;-):

Similar position 2 on 10×4  

f3etoiles: I forgot to mention that, many years later, I discovered a new kind of seki based on this configuration:

New kind of seki based on similar positions  

The reason this one is a complete seki is quite new: Now, if White adds a move she loses at least one group, but if Black fills a liberty, White fills the corresponding one on the other group reverting to the previous position, where White will at her leisure capture first the square bloc, then the T block, and mark 11 points . . .

The only other seki of many groups against one  

Robert Pauli: Let's fit it on a 10×10 (9×9 seems to small):

Here, the seki can be broken! (I wanted to call the way to do it a necanism, in homage to the father of Radek)  

Solution

Robert Pauli: Would you call this one seki, Denis?

Test for Denis  

f3etoiles Mmm. I did count, but might be wrong, as I find White still gains 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 points) I would call it a non-terminal seki, at least . . .

Robert Pauli: Under territory scoring, White gains zero by sacrificing her left side - she ends with 10 points territory and 12 captives, just like Black - but since she 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 [the captive Black hands over to balance moves]). By J89 rules this is seki, but a case can be made for one point without capturing. ;-)

Is it really an asymmetrical 3-group seki?  

To please Robert Pauli, here is a 6×6 version:

Asymmetrical 3-group seki on 6×6  

Robert Pauli: Thanks, Denis, but this one is smaller, plainer, and more balanced (too bad not one black stone can be reversed):

Asymmetrical 3-group seki on 4×8 by Robert  

f3etoiles No, it is correct (well, as far as 4×8 games go), as the last moves could have been, for instance

Asymmetrical 3-group seki on 4×8 by Denis  

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 (move lower right stone in square to upper left corner) enables a sacrifice! White can trade her small eye to bring life to her big eye:

Robert’s asymmetrical 3-group seki on 6×6  

Move whatever you feel to the discussion page.

Both players have passed. Is this an anti seki?  

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.
Under Japanese 1989 rules this would be a (technical) seki, due to (five) dame in the center. Worse, even the surrounding stones get infected, since dead stones (the one-eye groups, nothing else) on non-dame are treated as if gone while the disease jumps between stones and space.

Rubyflame: No matter who starts? It sure seems to me that whoever moves first wins.

Robert Pauli: Hmm . . .

Anti-seki? Black starts  

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.

Anti-seki? White starts  

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: Ouch, 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:

Anti-seki? shrunk?  

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.

Bent-fours in seki  

Warp: How about this one? According to my own analysis the corner groups are in seki under all rulesets (including Japanese 1989).

tderz: Source is most probably this excellent The undead bent fours in the corner, yes because it's the same Warp!

Seki on 4×6  

Notice that the seki may remain even when both sides are separated by unconditionally alive groups:

Circular hanezeki  

This situation is especially counterintuitive: the main semeai is me-ari me-nashi (one eye vs no eye), but it is nevertheless a complete seki, with 5 unplayable mutual liberties (it is possible to get up to 14 mutual liberties by enlarging the nakades . . .)