# Shapes related to the carpenter's square

Keywords: Life & Death

## Shape 1

### No outside liberties

Shape 1

Without outside liberties, White can kill by a ko.

Ko

The ko sequence. at a also leads to ko.

Variation

should just die.

Black mistake

is a mistake. The result is one eye to none, Black cannot approach and loses the capturing race.

Black mistake

is wrong. After , and are miai, Black is dead.

White mistake

cannot kill, the result is a seki. The reader may verify that at a does not work either.

### With outside liberties

Shape 1

With an outside liberty, the result is still a ko.

Example sequence

This is an example sequence.

## Shape 2

### No outside liberties

Shape 2

This one looks alive. But without outside liberties, White can kill.

Killing sequence

White makes use of Black's shortage of liberties with and .

No eye

If here, then after , Black cannot play at a.

If makes an eye here, then is atari, which allows White to destroy the eye at the corner.

### With outside liberties

Shape 2

With outside liberties, White can still get a ko. (same as Gokyo Shumyo, Section 3, Problem 78).

Ko

clamping at the 1-2 point is the tesuji that allows White to kill by a ko. If at a, the at b is also a ko.

White mistake

Connecting underneath at allows to live without ko.

## Shape 3

### With an open side

Shape 3

For a detailed analysis of this position, see L-group on the 4th line.

## Carpenter's Square with an extra leg

Black is alive in seki
Black is alive.
Failure: defending from the wrong side leads to a ko.