Gokyo Shumyo, Section 2, Problem 1 / Comments

Failure 3: ko??  

tderz: White fails.
With a different it looks like ko too.
Black cannot connect at a as b is nakade.
What happens if Black plays at c?
However, see ^[10] below. White failed twice with and .

Failure 3: double-ko life  

tderz: [10] is atari and it looks like ko but, it is life by double ko at b and .
Hence, the price for White's two wrong moves (previous ) and here is, that the status of Black's group deterioated from plain dead over ko with White taking first, to life in double ko (providing at least endless ko threats around 26 points).

c) Failure 3: seki  

tderz: [70] If thus White continues with here ... lets it end in seki (life).
Black is not fast enough to squeeze with a and c
as White will fill liberties b and d.
See transposition ^[60] above.