If blocks, then
occupies the vital point and turns the bottom eye into a bulky five dead shape in sente. Note that Black cannot connect by capturing with
.
Directly occupying the vital point at allows
to save half of his group. For the purpose of this problem, this result is considered a failure.
Notice that is the same point as
of the solution, and
threatens to connect out to the left side (as in this diagram) as well as to make a seki at the bottom side (see next diagram).