Gokyo Shumyo, Section 1, Problem 70 / Solution

Traditional Solution  

White plays on the leg side, on the second line. White lives up to . If next Black a...

Shortage of liberties  

White can play atari at and Black can't connect at (oshitsubushi).

Alternative solutions  

In addition, at a to c all live, at least with seki. See /discussion on a.

Failure  

Bending in from the side without the leg leads to ko. If Black wins the ko, he almost fills White's eyespace with a bulky five. The points a and b are miai for that purpose, and thus serve as a ko-threat for White:

White'slocal ko threat  

is a ko threat. If fills the ko, at makes seki.