is the vital point. It clearly makes one eye at the circled point, and White can't prevent another eye to the left of
.
Note what a difference an extra white stone at a would make.
Again, an extra stone at a would make the difference.
Once the vital point has been played - in the main line - the rest is not so difficult any more. Finding that point is the main challenge here. Let's have a look at how things can go wrong.
One is tempted to cover the two-space gap with a move like here. However, White strikes at the vital point. If
at
, then
at
.
This results in ko.
Go to Problem 41