Gokyo Shumyo, Section 1, Problem 61 / Solution

Black lives  

is the vital point.

Continuation (iii)  

This is probably the main line, since it results in a gote seki for Black.

Continuation (iv)  

White can play on the first line as in this variation, but Black still gets two eyes.

and are both on the line of symmetry - even though the stones aren't completely symmetrical, the eye space is.