Xuanxuan Qijing Problem 130 / Solution

 

is the key, has to prevent from escaping. After , black can't approach from either side. Alternatively, at 'a' also works.

 

If black plays here, does the same trick. Alternatively, 7 at 'a' also works.

in this diagram is not as good  

in the previous diagram is better, because with ouside help, black can try to escape like this.

Failure

This atari doesn't work either.  

Don't play at 'a', or white plays and kills.

 

If black just secure the eye in the corner with . at 'a' also works.

 

After , the best white can do is getting a ko with x or y.

Don't get confused!!

It is important to notice where the outside liberties are. Let's look at this related problem.

A similar problem  

'a' no longer works because of the liberty at 'x'. It won't be explained here but at 'b' is the killing move for this black group.

 

This is the original problem, do you see the difference?

Video

Without external liberty:
Life and death problem 001 on Michael Redmond's Go TV
With outside liberty:
Life and death problem 002 on Michael Redmond's Go TV