Shapes related to the carpenter's square

    Keywords: Life & Death

Table of contents

Shape 1

No outside liberties

[Diagram]

Shape 1

Without outside liberties, White can kill by a ko.

[Diagram]

Ko

The ko sequence.

[Diagram]

Variation

B4 is an interesting resistance, but W5 ensures a ko.

[Diagram]

Black mistake

B4 is a mistake. The result is one eye to none, Black cannot approach and loses the capturing race.

[Diagram]

Black mistake

B2 is wrong. After W5, B6 and W7 are miai, Black is dead.

[Diagram]

White mistake

W7 cannot kill, the result is a seki. The reader may verify that W9 at a does not work either.


With outside liberties

[Diagram]

Shape 1

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

[Diagram]

Example sequence

This is an example sequence.


Shape 2

No outside liberties

[Diagram]

Shape 2

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

[Diagram]

Killing sequence

White makes use of Black's shortage of liberties with W1 and W3.

[Diagram]

No eye

If B4 here, then after W5, Black cannot form an eye at a.

[Diagram]

Also dead

If B4 makes an eye here, then W5 is atari, which allows White to destroy the eye at the corner.


With outside liberties

[Diagram]

Shape 2

Without outside liberties, White can still get a ko.

[Diagram]

Ko

W3 clamping at the 1-2 point is the tesuji that allows White to kill by a ko. If B4 at a, the W5 at b is also a ko.

[Diagram]

White mistake

Connecting underneath at W3 allows B4 to live without ko.



Shape 3

With an open side

[Diagram]

Shape 3

[Diagram]

Proposal

BramGo: Is this correct?

[Diagram]

B cannot win the liberty race

With no outside liberties on the 4th-line L group, W can kill without needing a descent to the second line.

[Diagram]

Without an outside liberty, the best that W can get is a ko, by forming the carpenter's square.


The above is not correct. See L-group on the 4th line.


Carpenter's Square with an extra leg

[Diagram]

Black is alive in seki

[Diagram]

Black is alive.

[Diagram]

Failure: defending from the wrong side leads to a ko.


See also:


This is a copy of the living page "Shapes related to the carpenter's square" at Sensei's Library.
(OC) 2014 the Authors, published under the OpenContent License V1.0.
[Welcome to Sensei's Library!]
StartingPoints
ReferenceSection
About