Bulky seven in the corner

    Keywords: EndGame, Life & Death
Bulky seven in the corner  

If White plays first, this shape becomes a seki or a 10,000 year ko. Unless White is komaster, Black will normally play elsewhere, as White only threatens a 10,000 year ko, and the best Black can do is seki, while in the original position Black could live with 6 pts. of territory.

(If Black has 2 or more outside liberties, White cannot prevent Black from capturing the two white stones.)

(Note that if black chooses to play elsewhere and accept a possible 2-step ko, he must do so after 3. If black tenukis after 1, white kills with 2 then a3. kevinwm)

In the endgame Blacks can turn this shape into a living group with 6 points of territory by playing at W1.


In this position Black can play at B1 or a to make seki.

Both players would prefer that the other fill a first (White must take B2 before filling a). Since White has to play here four extra times (W3, W5, W7 captures B2, and W9 finally fills in a) and have an extra ko threat to win this, it will be very hard for White to find time to start this, but it might be possible depending on the rest of the board. The rest of the game (after white plays W5) might become a fight to get an extra ko threat!

Variation 1  

Black could also make seki this way. But this B2 is worse technique, as B4 is absolutely necessary; Black does not have the choice to omit B4.


B4 elsewhere.

If Black omits B4, W5 kills.

Variation 2  

W3 threatens to make a two stage ko at a instead of a 10,000 year ko. If White captures the Black group, it will take one less play than the 10,000 year ko. However, if White is komaster Black will make seki at a, anyway. W3 is technically inferior because it allows B4 if Black is komaster.


This W1 is wrong. After B4, White cannot fill the ko, while Black can resolve it at any time.

See also

Bulky seven in the corner last edited by on January 26, 2011 - 17:20
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