Carpenter's Square

All you need to know about Carpenter's Square-31

Diagram 31.1: White to play

This shape is very similar to Shape 30.

Diagram 31.2: Solution

The solution is similar too. is still the key point and black corner suffers the same fate as in Shape 30.

Diagram 31.3: Variation

does not work either. White has longer liberty. Note that white cannot play though.

Diagram 31.4: White fails

is incorrect. is important to form a ko. If black connects at first, allowing white to occupy , the corner would be dead.

To summarise: this is another simple problem. The tesuji in Diagram 31.2 should be memorised.