Carpenter's Square

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.

The discussion is divided into an easy part and a difficult part. More discussion is found at the weak carpenter's square.

Table of contents Easy part Difficult part No outside liberties One outside liberty See also Book references Online references

Table of diagrams Carpenter's square Basic ko (no outside liberties) Continuation Throw-in ko One outside liberty One outside liberty The basic method fails Continuation

Easy part

Carpenter's square  

The black formation in this diagram is the carpenter's square. The vital point is a: Black can play there to live. White can play there to turn the corner into ko.

Difficult part

No outside liberties

Basic ko (no outside liberties)  

The best way to set up the ko depends to a large extent on the number of outside liberties of the black group. If Black has none, White starts by playing on the vital point. Black attaches on the first line, and White stretches in the other direction.

Continuation  

White further reduces the black eye space and after 5, the only way left for Black to live is engage in a ko.

Throw-in ko  

Bill: If , after 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.

One outside liberty

One outside liberty  

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

One outside liberty  

Black 4 in the previous diagram is forced: here's how Black dies by playing atari.

The basic method fails  

Here's why the basic method fails when there is an outside liberty. Everything goes smoothly for White until 6.

Continuation  

However Black squeezes White for two eyes with 2 after White first captures the ko.

See also

• Weak carpenter's square
• Carpenter's Square - Wrong Attack
• Shapes related to the carpenter's square
• Joseki-related life-and-death example 8

Book references

• Get Strong at Life and Death Part 1 Section 9
• Life and Death Chapter 29 and 30
• Think Like a Pro Pae page 103ff

Online references

• All you need to know about Carpenter's Square

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 . With 0 liberties, you can do without.

[1] Literally, a 180 ml. measure. Here is a picture.