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Eyes Win Semeais
Difficulty: Advanced
Keywords: Proverb, Life & Death, Tactics
The proverb 'Eyes win Semeais' means that in a semeai, if one group has an eye and the other has not (in Japanese the term 'me-ari-me-nashi' is used for this situation), the player with the eye usually wins. An example of this proverb at work can be found in this diagram: At first sight white has 6 liberties and black has 5, so if we just count the liberties, it seems that white would win the semeai even if black went first. The truth is rather the opposite: Black will win, even if white goes first. The reason for that is black's eye at A. Because playing here would be suicide for white, it is necessarily the last liberty she will fill. White will have to fill the shared liberties (5 and b) first. To correctly count the liberties in a situation like this, use the following rule: Rule: If one group in a semeai has an eye, and the other does not, all shared liberties should be counted as if they were liberties of the one-eyed group only.
There is a second, less known (and in general also less important) way in which eyes influence semeais. An example of this can be found in this diagram. Black and white both have four liberties. Black has an eye and white does not, but at first sight that does not seem to matter, because there are no shared liberties. Nevertheless, white is not able to win the semeai, as this diagram shows. The reason for this is the approach move that white has to make with white 5. At first sight, black has a similar approach move problem at A. However, this problem does not worry black, because he can simply solve it by making B the last liberty that he fills up. White on the other hand, is forced to play the eye as the last move - so she has to make the approach move first. Put as a rule: Rule: If there are no shared liberties in a semeai, each player can omit the necessary approach moves for one liberty, but not if his/her opponent has an eye.
See also counting liberties.
-- Andre Engels (2D Europe) This is a copy of the living page "Eyes Win Semeais" at Sensei's Library. (C) the Authors, published under the OpenContent License V1.0. |