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 is the same, but this time White kills the corner by playing at a.
That is, the fact that the stone here is white, rather than Black, changes a the status of the group from ko to unsettled status.
Bill: Quick question: Does the weak carpenter's square need the
stone? With that stone there White can kill by cutting, for instance.
willemien No
After a and b are miai a White play a creates a squared four while a White play at b forces black to connect at c reducing his eyespace to a bulky five
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
.
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 1 and 3.