Gokyo Shumyo, Section 1, Problem 79 / Solution

Main line  

The key move here is the descent at , threatening to connect underneath while making shape. After , Black has two eyes: at the circled point, and in the corner.

Variation at 5  

If Black draws back to , White plays hane at and reduces the black group to an L-Group (White can indeed not play at the marked point). With no weaknesses to exploit, Black is dead.

Variation at 7  

instead of in the main line, makes sort of a J- Group. The result is ko.