Tristram1:
I think one of the listed solutions is incorrect. After 1. B a17? 2. W b18, neither I nor Katago can find a way for B to live. For example, if 3. b19, 4 a18 5. e19, 6. c18 kills. If B doesn't play 3. b19, w can just continue with either b19 or c19, to make a dead shape. I believe b18 is just the vital point here - 1 b18 is the only way to live.