Beginner Exercise 128 / Solution

White kills  

kills. After , Black can't play at a for shortage of liberties.

Continued  

White connects out to the marked stone.

Variation  

is obviously too slow.

Failure: ko  

Attaching on the other side, , fails. After , White can't connect at a for shortage of liberties. The result is a ko, not as good as the unconditional kill.