The descent at is key for life. If
makes a placement, then
and
forms a seki. This is the main line.
If plays the hane, then
divides the eye space into two eyes very nicely. White cannot cut at a because of shortage of liberties.
Descent on the wrong side. The points a and b are miai for the kill.
is a greedy move that fails.
followed by the throw-in at
reduces Black to only one eye.
See also: