Shapes Related To The Carpenters Square / Version 20090527

Shape 1

unkx80: It seems to me that shape 1 is alive. If this is true, much of the contents of this page needs to be revised.

1. No outside liberties

Shape 1

In addition, we will assume the marked stones, so as to give Black no escape routes to the outside. In this case, White can kill by playing the obvious placement at a.

Killing placement

We will consider the following answers by Black: the hane of a, the descent of b and the perhaps less obvious placement of c.

Var 1: hane

After , a and b are miai for the kill:

Var 1.a

Black will eventually be forced to fill at a, after which his eyespace is almost filled with bent three. If White omits , Black gets at least seki by playing there

Variation 1.b

Less intuitive perhaps is this variation. makes an eye in the stomach. White will eventually be able to fill the inside liberties. If Black does so, his eyespace will become almost filled with a pyramid four killing shape.

Var 2.a: descent

In this variation, the outside liberties are important. Black puts up resistance, but White makes an eye in the stomach. She counts the inside liberties for a total of three. Black has only two outside liberties and falls short.

Var 2.b: descent

If here falsens the eye.[1]

Var 2.c: descent

If here, makes miai of a and b to either reduce Black's eyespace to three in a row or make an eye in the stomach with a pyramid four shape.

Var 3: placement

The cunning placement of reverts to the above. is again the key point.

Var 3.b: mistake

If White connects with , makes it a seki.

Var 3.c: mistake

If here, Black makes it ko.

Var 3.d: mistake

Var 2.b: descent

Nope... after , a and 4 are miai.

2. Outside liberties

Var 1: Alive

If Black has an extra liberty, this variation doesn't work anymore. Black lives through capturing a bent four.

Var 2 : life

Same thing

Var 3: ko

If here, now sets up a ko.

Var 4: placement

The placement too works.

Var 5: placement

As with this seki.

Shape 2

Shape 2

This one looks alive. Any attempts ?

Matthew Woodcraft: I can't see a way to kill.

Failed attempt 1
Failed attempt 2

Charles Matthews I believe ko is the correct answer.

Shape 2