Tsumego From Games 11 / Solution

 

White is better. The reason: Black a does not threaten to kill:

 

If is elsewhere and Black captures with ...

 

... White recaptures by playing under the stones.

 

If White plays here instead of the correct answer, threatens to kill because now there is not enough room under the stones. That means that is a bigger ko threat than when White plays at a instead of .