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||Table of diagrams
Basic ko (no outside liberties)
One outside liberty
One outside liberty
The basic method fails
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.
This is not as good for White as the previous Continuation diagram.
Black 4 in the previous diagram is forced: here's how Black dies by playing atari.
Here's why the basic method fails when there is an outside liberty. Everything goes smoothly for White until 6.
- Weak carpenter's square
- Carpenter's Square - Wrong Attack
- Shapes related to the carpenter's square
- Joseki-related life-and-death example 8
- Get Strong at Life and Death Part 1 Section 9
- Life and Death Chapter 29 and 30
- Think Like a Pro Pae page 103ff
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.