Weak Carpenter's Square
Keywords: Life & Death
The weak carpenter's square is a carpenter's square without the connection. 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 ko status to unsettled status.
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.