312WS Notcher

    Keywords: Life & Death

Table of contents

Without external liberties

#3 #1 #4 #2 #5 #6

This notcher is just as dead as his brother, the 312WW Notcher. That's provided that Black has no external liberties, otherwise Black can get a ko.


Main line  

Black first invites a ko, then expands his eyespace as much as possible. The throw-in at W6 is necessary to reduce it to an almost fill with three.

First option  

There is no ko.

Wrong continuation in the first option  

W2 allows for a ko.


Second option  


Third option  

This reduces to a 222SS notcher with White playing first. It is killed by the hane at W2.


Fourth option  

W2 is the vital point, black can answer at B3, W4 or a, but it all fails. Note that W6 works because Black has no external liberties (Black would put the group in atari if he tries to make a second eye by playing at b).

If Black does have an external liberty, however, W2 would not work. In that case, White can only go for a ko.

Wrong continuation in the fourth option  

W2 allows black to live unconditionally.


Fifth option  

W2 is the vital point again. If instead W2 at 4, B3 at 2 leads to ko.


Sixth option  

W2 holds Black to one eye.

With an external liberty


312WS with an external liberty  

When there is an external liberty, B1 results in a ko.

312WS with an external liberty  

The attack used for the "no external liberties" case is repeated here to show that an unconditional kill is not possible. Since there is one external liberty, Black can safely play B7 to make a second eye.

312WS with an external liberty  

Here is an example of a sequence that leads to ko. Although White does take first, Black may be able to use a as a local ko threat if the escape to the center is possible.

312WS Notcher last edited by TheBigH on February 3, 2016 - 08:18
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