Seki unambiguous definition discussion

Solution for seki in general

Presume the Japanese 2003 Rules / version 35a. Then use the following citation:

Subject: Group, Seki, Eyespace: Definitions Date: Tue, 18 Nov 2003 18:37:42 +0100 From: Robert Jasiek Newsgroups: rec.games.go
RGG: http://groups.google.com/group/rec.games.go/msg/e7cf3b4ec0848f3f

"Definition: A black-group is the union of all black-strings of a black-region.

Definition: A white-group is the union of all white-strings of a white-region.

Definition: A group is either a black-group or a white-group.

Note: For other purposes one might want to define group differently.

Definition: An in-seki-space is a dame and, recursively, any adjacent dame or any adjacent intersection of an in-seki region.

Definition: A seki is the union of all strings of an in-seki-space."

Note: One can argue that there are Matti Siivola's other non-independently-alive groups without a dame that are seki-like. The definition above does not include them.

Proposal for simple seki

All simple sekis are some subset of all sekis.

Definition:

1. A mutual liberty is an empty point that reaches two chains of different color.
2. Two chains of different color live in simple seki if they reach no empty points but the same two mutual liberties.

Addition:

1. A group of stones is alive in simple seki, if for any sequence of moves by the opponent, there is a sequence of answers that turns the group into a chain which is part of a pair of chains, complying with definition 2.

Seki  

(TapaniRaiko: The proposal is not enough, as these two examples show. I have seen an example where a 35x35 board was filled with small groups all living in a single seki.)

Not a seki  

[edit]

Discussion

How about something along the lines of:

"A local position with at least one mutual liberty or single point ko which cannot be filled by either side without incurring a loss." We still have to read out the consequences of moves, but I think this captures what we mean by Seki and applies to all the examples there.

jvt: This is still ambiguous: how to define which chains belong to the 'local position'? Some chains may be in seki even if they are not adjacent to any dame.

RobertJasiek: Needless to say, the Japanese 2003 Rules will provide an unequivocal definition of "seki" under those rules. For other rules, minor modifications would be necessary then.

KjeldPetersen: If a group (with max 1 eye) is moving out (not filling the eye) and thereby get into a position of atari, then this group is posible part of a seki? Look at the example at the top. All three groups will go into atari if they move out.

Chris: The definitions given here are a bit naive. For all of them it is not very difficult to come up with couter-examples. I don't think an attempt to define seki by the possible shapes that are seki will succeed. A position is a seki because of the possible sequences in the position, not because it has a particular shape. Hence, it is probably impossible to define seki without referring to a search. For computer-go it is important to know what is seki. I wrote a seki-recognizer that I hope is not too inaccurare. Here is more info.

Michael?: A definition based on game theory. A seki is any position which locally has a value of *. http://en.wikipedia.org/wiki/Star_%28game_theory%29

Superdave: No, star means unsettled--whoever moves first wins the local position. 0 is the CGT value that means whoever goes first loses, which would be a better analogy for a seki, except that CGT models games where you are not allowed to pass.

Michael?: Ah, you're right, it's been a while since I read winning ways.