Xuanxuan Qijing Problem 238 / Solution

Solution  

Black can't make an eye in the corner.

A Basic Shape

 

This is a shape that occurs in many tsumego problems.

and at , above  

Black captures some white stones through snapback.

 

However, there's no eye in the corner for black.
See also Xuanxuan Qijing Problem309 for another problem with this shape.

Failure

 

As long as is not at , black is alive after .

 

Notice now the snapback in the corner result in this, which is differenct from the shape before.