is the vital point.
After , if B a, then W b. If B b, then White captures four stones (connect and die).
If is at , prevents a second eye, as in variation 1.
( could also be at . If then , .)
Iago not saying the previous variation doesnt work, but isnt this simpler for the same result ? if black goes for a ko, white can atari with W a unless I am missing something (number of ko threats?)
hhw: Black will first play at b. It looks to end in only ko.
After secures , prevents a second eye.
and are miai.
After , prevents a second eye. Even with Black cannot create an eye in the corner.
If is at , reverts to variation 1.