RTG Problem 101 / Solution

Black is dead  

removes the potential eye at in sente, makes a false eye in sente, and removes the potential eye at . Note that is connected to the outside white stones by a box connection.

Only one eye  

If black captures the white stones inside, the placement keeps black dead. Now a and b are miai.

Order is important  

The order of moves is important. If white plays first, black can salvage half his group with .