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.

But what about:
[Diagram]
Variation  

B4 should just die.

[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:


Shapes related to the carpenter's square last edited by 212.204.102.90 on July 18, 2018 - 22:03
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