GokyoShumyoSection4Problem78/Solution

key move  

Famous problem for its unexpected difficulty. It's not too hard to find the first move (everything else fails very quickly), but the follow up is difficult.

(There is some nice discussion of this problem in the Fujisawa tesuji dictionary.)

continuation  

Simple connection is defeated by .

continuation  

So White occupies the point himself. Then ! is the decisive blow. White is short of liberties and can't play at a.