Kyu Exercise 87 / Solution
A simple analysis here. It should be easy to see that here lives, saving at least the right side of the group.
Thus is the vital point. The next thing to see is that if makes an eye in the corner, then can cut the Black group into two. Please observe that is connected to either or by the box connection.
Also note that a and b are miai, so there is no eye there.
If connects, then destroys the eye in sente because it threatens to cut the Black group into two.
If here, then kills.