Beginner Exercise 82 / Solution

Solution  

saves the group, because White cannot atari the L-shaped chain with a good result - a White move at either a or b is a self-atari. Subsequently, and are miai for unconditional life with two eyes. In particular, after , White at a is still a self-atari.

Failure  

is a failure, because is an atari on three Black stones, reducing the corner eye space to a single eye in sente. If connects, then destroys the other eye.