TsumegoFromGames61/Solution
tderz: I would guess to and due to shortage of liberties, black cannot make a 2nd eye with ->a.
- ->b only leads to ko after ->.
- -> is black alive after ->b with miai -> 1 or 5.
- If ->, ->b, ->1, ->, ->4, ->, W takes at a and black presses at c.
- If -> 3, ->2, ->5 (no threat to link up), ->b dead shape (no seki escape)