Gokyo Shumyo, Section 1, Problem 72 / Solution

Continuation  

White lives in seki because Black can at most almost fill her eye space with a bent four.

Variation  

As you can see: 4 and 5 are miai.

Failure at 1  

There is death in the hane : The door group is dead.

Failure at 5  

If White answers the marked stone (Black 4) with 5, Black kills with 6 by making miai of a and b.