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.