xela: white can't play 'a' (shortage of liberties)
xela: Some time later, this occurs to me... (if at a then I think it leads to ko)
unkx80: Is this another solution?
xela: What about at a?
symplicity: Then it looks like black can just play atari starting at b and eat white.
jms: White absolutely cannot allow Black to push in at 'a'. Even if @ 'b', then @ 'a' kills the White group.
jms: White's only chance is to try , after B takes the vital point with , White is ruined. W cannot play at 'a' or 'b' due to a shortage of liberties.
jms: If @ 'a', then @ 'b' kills. If @ 'b', @ 'c'.
jms: Whether W tries 'a' or 'b', Black can calmly play 'c' to catch the 2 white stones. (In the case of @ 'a', it will be a snapback).