Beginner Exercise 283 / Solution

Solution 1  

The first solution is to jump down to the first line at and throw-in with .

Solution 2  

The second solution is to block with . Note that is the only way to have a chance of killing the whole group, and thus we revert back to the first solution.

Solution 2 variant  

If here, then lives. (White gets to capture the marked stones in sente. Solution 1 doesn't give this option to White)

Comment  

In both solutions, Black can choose to fight the ko with instead. Here, a becomes a local ko threat for Black.