Carpenter's Square

  Difficulty: Expert   Keywords: Life & Death, Ko

Chinese 1: 斗方 (dÚufāng)
Chinese 2: 金柜角 (jīngužjiăo)
Chinese 3: 曲尺 (qūchĭ)
Japanese: 一合マス (ichigou masu) [1]
Korean: 됫박형 (doetbakyeong)

The so called carpenter's square is one of the most complicated of the basic life and death positions. It is said that anyone who completely understands the shape is at least professional shodan. It was misunderstood until the 1300s. It is simple enough as far as its vital point and status are concerned - it almost always results in a ko. However there are endless ways to set up the ko, and even more ways to defend incorrectly and end up dead anyway.

"See Also" section has links to closely related shapes.

Table of contents Table of diagrams
[Carpenter's Square]
Basic 2-2 attack
Continuation
Throw-in ko
Alternative: clamp
Variation
White's option
One outside liberty
One outside liberty
The basic method fails
Continuation


Summary

The Black formation in this diagram is the carpenter's square. White a to c all lead to ko. When Black has one or more outside liberties, only a works. Black to play can live with almost any move.


Details

No outside liberties

[Diagram]
Basic 2-2 attack  

a) W1 2-2 placement is the basic way, because it works even when Black has outside liberties or outside hane at a. Black must attach on the first line. Now White has many ways to start a ko, for example by W3 bump in the diagram.

[Diagram]
Continuation  

White further reduces the black eye space and after W5, the only way left for Black to live is engage in a ko.



[Diagram]
Throw-in ko  

Bill: If W3, after B4 W5 makes a throw-in ko at a or b. White can also make seki at a.

This is not as good for White as the previous Continuation diagram.


[Diagram]
Alternative: clamp  

b) Against W1 clamp, B2 is the only defense leading to a throw-in ko, with White taking first.

[Diagram]
Variation  

Natural looking B4 is a mistake. After W5, Black can't play at a! This line depends on outside situations; Black may escape by playing at any of b.

[Diagram]
White's option  

W3 connect underneath leads to another ko. Black takes the ko first.


c) For White's hane (c in the summary), see Shikatsu Myoki Tsumego Series 123 and Shikatsu Myoki Tsumego Series 124.

These alternatives, b) and c), are important because White can choose the direction of the resulting shape; in other words, which side (left or upper) is more affected by the ko fight. On the other hand, a) 2-2 attack above allows Black to choose.




One outside liberty

[Diagram]
One outside liberty  

With one outside liberty, White sets up the ko in a different way.

[Diagram]
One outside liberty  

B4 in the previous diagram is forced: here's how Black dies by playing B1 atari.

[Diagram]
The basic method fails  

Here's why the basic method fails when there is an outside liberty. Everything goes smoothly for White until B6.

[Diagram]
Continuation  

However Black squeezes White for two eyes with B2 after White first captures the ko. The extra liberty at a tells.


See also

Book references

Online references


It seems that one as white, one would only need to learn the method that works with 2 outside liberties, as it will also work in 1 and 0 outside liberties. As black, the other variations I suppose have some value in knowing why they don't work (or work as well for white) in the 1 and 2 liberty versions... Or have I missed something?

(Sebastian:) The difference is that the edges have to be better protected. In diagram "Two outside liberties", you need the marked stone white+circle. With 0 liberties, you can do without.


[1] A wooden box used traditionally in Japan to measure one gō unit of volume, which is almost exactly 180 ml. Ichigou masu translates simply to "one gō measuring box".


Carpenter's Square last edited by hnishy on February 19, 2023 - 02:51
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