Gokyo Shumyo, Section 1, Problem 78 / Solution

Solution.  

The tesuji is .

Main line  

at a and can't play at b because White captures three in a row, assuring a second eye.

Variation 1.  

This lives. Covered in Beginner Exercise 56 and Beginner Exercise 58.

Variation 2 (Main Line).  

The next tesuji is , sacrificing yet another stone.

Failure 1  

If White fires off the usual sequence first only to play the former tesuji at , she falls short as a is now suicide.