posetcay: Actually if black wants to avoid ko, black should descent at B18 as first move instead of D18 so your variation would be inferior to that. In that case should we also flag D18 as a mistake since it leads to ko and make B18 the only correct answer?
posetcay: W P2 is the wrong resistance, it becomes ko if W descend at R1 instead, I have uploaded the SGF with the correct variations. I recommend either removing N4 stone to give B one more liberty or switch the correct solution to ko (black takes first).
waanotan: i think black can live with tsuke nobi at the corner - w cut but b
sacrifice thus 3 stones if atari next
w can’t cut - b connect
b B18/wC16/ b D18/w E15/B C18 - live in gote - dunno how w kill this shape
Ivan Detkov: You answer is inferior to the correct solution.
B18 is an unconditional life and D18 is a Ko. Why do D18 is an answer here?