Lyde: [current position] Why is this marked incorrect? Ko should be a success (since there are not enough liberties to squeeze from outside). It seems to me that C16 is a mistake for the defender
MELIKETACO: If this is a seki then it is an endgame problem and should be marked as such. If we start at b17 then it will become a thousand year ko[current position] + A17
posetcay: Opponent will answer B17 with B18. There is still a sequence that leads to seki after starting with B17 that I missed previously, so I added that. Also since this isn't a beginner collection, there is no need for hints like ko or seki.
Met: There is the ko as Kovarex says; Maybe it can be avoided in posetcay's variant. But imo W can enforce the ko here already.
[current position] + A18
Removed C4 to avoid confusion.