Odd eyed seki

  Difficulty: Advanced   Keywords: Rules, Theory

In a seki where White and Black have a different number of surrounded points, the score varies over rulesets.

It does not depend on the choice of territory or area scoring. What matters is whether eyes and false eyes in seki are considered territory.

In AGA, Chinese, French, and New Zealand rules, they count towards a player's score. Under Japanese and Korean rules, they are not worth points to either player.

Whilst territory and area scoring usually differ by only one or zero moku, treatment of surrounded points in seki can result in a significantly greater difference.

Odd eyed seki  

In this seki, White encloses six points, but Black just one. x is neutral (shared) under all rules.
There shall be no komi nor prisoners.

So, the five circlemarked points decide the game:

 points in seki  ||       Area scoring              |       Territory scoring
   treated as    ||          gives                  |             gives
                 ||  (e. g. Chinese rules)          |   (not commonly used)
                 ||                                 |
 territory       ||  Black: 39.5                    |  Black: 11.0
                 ||       = 39 points + 0.5 shared  |       = 11 territory + 0 captives
                 ||  White: 41.5                    |  White: 13.0
                 ||       = 41 points + 0.5 shared  |       = 13 territory + 0 captives
                 ||                                 |
                 ||  -> W wins by 2 moku            |  -> W wins by 2 moku
                 || (this case doesn`t make sense)  |  (e. g. Japanese rules)
                 ||                                 |
 unscored        ||         XXXX                    |  Black: 10.0
                 ||                                 |       = 10 territory + 0 captives
                 ||         XXXX                    |  White:  7.0
                 ||                                 |       =  7 territory + 0 captives
                 ||                                 |
                 ||                                 |  -> B wins by 3 moku

Djaian : Huh?, I just have a question, and I am not sure, but isn't there "the pass stone" rule in japanese rules? Suppose it's black turn, he will pass, and thus give a stone to his opponent. Now white fills one of the circle dot (a false eye, not the real one ! ). Black passes again, and give another stone... And so on. So the final score should be the same whatever the rules. Am I right?

I think that is the reason for the pass stone rule. Of course, in chinese rules, no need of a "pass stone", since scoring is the same if the circle dots have white stones or not.

Can someone tell me if my reasoning is correct?

Herman Hiddema: The pass stone rule is specific to AGA rules, it is not used in Japan, Korea or Europe. Using pass stones basically means that under AGA rules, scoring is area scoring, and the pass stones allow you to count in the way of territory scoring. The reasoning you give about how the score works out with pass stones is correct.

Djaian: Thank you for your answer. So this means there is actually a difference if we count according to Japanese rules or Chinese.

Note that the asymmetry examined here concerns seki territory only. Sometimes, another asymmetry is interesting, which is the area? tally of the seki (territory + stones). About that, see 10000 Year Ko and seki collapse.

Karl Knechtel: This isn't what I would think of as a true case of an odd-eyed seki, because here it is possible for White to fill the 'o' points. There is at least as much controversy to be found in distinguishing those cases from those in which she can't:

Should a count?  

In the above case, I would consider it a deficiency of the Japanese rules not to count the eye points, as it goes against the spirit of what territory is supposed to be: a place where you can safely play later. Here, though, that argument fails, but an argument could be made that it's inconsistent not to score the point here if you score the points in the above case :s


Should a count?  

Bill: I think that odd eyed seki is an odd name for the kind of position talked about on this page, since the number of eyes can be even or odd. Can anybody come up with a better page title?

Bbbbbbbbba?: In my opinion the "odd" doesn't mean "odd numbers" (like 1, 3, 5...). Instead it means "uneven, unpaired". As is stated at the top of the page, in this kind of position the numbers of white eyes and black eyes are different. Doesn't this make sense?

Odd eyed seki last edited by bbbbbbbbba on June 5, 2012 - 11:36
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