Weak Carpenter's Square

Weak carpenter's square  

The weak carpenter's square is a carpenter's square without the connection at the corner of the shape. The vital point of 2-2 is more emphasized and this time White kills the corner by playing at a. b and c may also kill depending on outside situations.

That is, without the black stone at , changes the status of the group from "White kills by ko" to "White kills unconditionally".

If Black plays first, almost any move lives. If is occupied by a White stone, only a works.

White can kill  

After a and b are miai: a White play at a creates a squared four, while a White play at b forces black to connect at c which reduces his eyespace to a bulky five.

White can kill  

If here, then to reduces the eyespace to rectangular six in the corner.

White can kill  

When the 4-4 point is occupied by White, there are many ways for white to kill after . This is just one variation After , at is an auto atari so Black has no other option than to let white connect at .

variation  

After a and b are miai

Endgame technique  

If Black has secured life by playing on the vital point, there is an important endgame technique for White to remember: the forcing moves at and .

not really a carpenter's square  

What about this one? Klaus

not really a carpenter's square  

Here's one sequence. Bob McGuigan

Book references

• Life and Death Chapter 30