wms's Dame-Seki Challenge

  Difficulty: Expert   Keywords: Life & Death, Problem, Question, Rules

wms: I have a problem, but I won't put it as problem of the month because it is not a "typical" go problem.

Lately in rec.games.go a discussion has sprouted up and KGS' implementation of Japanese rules. That jogged my memory about something I thought about a while back, but was never able to prove one way or the other. It occurred to me that it might make a nice problem for people interested in go oddities.

The problem comes from KGS' seki detection code. The goal of the KGS seki detection code is to always correctly spot seki, as long as both a) all dame that can be filled, are filled, and b) all dead stones are marked correctly.

But I thought of one situation that would make the KGS algorithm have an error. I think it is not possible for such a situation to exist, but I'll put it here, and invite people to try to find such a situation, or prove that it cannot exist:

Can you find a position where one player (black, let's say) has two one-eyed seki groups separated by a bamboo joint (or similar connected-by-dame-but-can't-connect shape) of white's. If black tries to push through the bamboo joint, black will die, but if white tries to fill one of the "gap" dame in the bamboo joint, then white will suffer some problem (either dying or allowing one or more black seki groups to become fully alive).

If anybody can find such a board position, then it will be interesting, and I will have to adjust my seki algorithm. If somebody can prove it can't exist, then that's great, my algorithm is fine.

If you want to know more about the algorithm itself, just use google to search rec.games.go for the terms "shubert" and "seki".

rubilia: [ext] Here's the direct link.

wms: OK, to help things along, here is an example position that is close but not quite there:

[Diagram]

Example that is close, but doesn't match, my requirements

This looks like what I need, but note that if black plays first, then black can connect, make life, and kill white by pushing through the bamboo joint; if white moves first, white can just fill the bamboo joint and end up killing both black groups. So this isn't even a seki at all, but it shows what I need - two one-eyed groups, separated by dame. I need a position like this, but where neither player can fill the dame separating the two one-eyed groups. Or, just as good, I need proof that in such a situation, one player will always be able to fill the dame.


impu1se: I think something like the second example under number 4 in StrangeSekis is what you're looking for. wms: No, #4 in strange sekis doesn't match - the two one-eyed groups are opponsing colors, so "connecting" them won't give a living group.


Like this? Neither can attempt to make a move inside the bamboo

[Diagram]

B Like this?


Because if you want them to have eyes it's clearly impossible as filling the dame and connecting would saperate the other 2 killing them... <- That's if I understand you correctly. Because 2 eyes always win vs anything else... And an eye wins vs none providing there aren't enough outside liberties - But if there it wouldn't make sense in the first place...

wms: The example above doesn't work, KGS/CGoban scores it perfectly - there is only a single one-eyed group. Again, look at my example above, the key thing is two one-eyed groups of the same color, connected by dame that neither player can fill. You say that it's clearly impossible, but I don't see that; my point is that filling the dame must be impossible. Don't forget, when you fill dame, you also under certain circumstances reduce your liberties - so there are cases where dame simply cannot be filled safely.

firefox04?: Wms, in your example, what if B attempts to capture the 2 stones?


(Sebastian:) How about awarding an annual [ext] KGSPlus membership to the winner?

[Diagram]

Maybe something along the lines of this?


Scatee?: Like this black has two eyes and neither black nor white can file those dames.


(Sebastian:) This Challenge was originall posted by wms in the KGS Go Cafe. Please feel encouraged to find a different name for this page. I'm not even sure if the "s" in "wms's" is correct.


This is a copy of the living page "wms's Dame-Seki Challenge" at Sensei's Library.
(OC) 2004 the Authors, published under the OpenContent License V1.0.
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