RTG Problem 89 / Solution

Solution  

The key move is this . It is wrong for to throw-in at a.

Variation 1  

The three Black stones cannot connect.

Variation 2  

Again, Black cannot connect after . Due to the presence of the stone, Black will be captured in a ladder if Black insists on connecting.

Variation 3  

The huge Black group is captured.

Failure ( at )  

Throwing in first actually allows the Black group to go home, due to the existence of the stone.