All you need to know about Carpenter's Square - 30

Diagram 30.1: White to play

This is one of the simplest problems in the series if white knows where to start.

Diagram 30.2: Solution

White 1 is a famous tesuji, simple and effective.

Diagram 30.3: White fails

White 1 is incorrect in this shape. A ko is inevitable.

Diagram 30.4: White fails

White 1 doesn't work either. Black 4 is important. The result is again a ko.

Conclusion: Remember the tesuji in Diagram 30.2 and it can be used in other situations too.