312WS Notcher

312WS  

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 is necessary to reduce it to an almost fill with three.

First option  

There is no ko.

Wrong continuation in the first option  

allows for a ko.

Third option  

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

Fourth option  

is the vital point, black can answer at , or a, but it all fails. Note that 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, would not work. In that case, White can only go for a ko.

Wrong continuation in the fourth option  

allows black to live unconditionally.

Fifth option  

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

Sixth option  

holds Black to one eye.

312WS with an external liberty  

When there is an external liberty, 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 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.