In a recent katago self-play game https://katagotraining.org/sgfplayer/ra ... es/547118/, just before black resigns, on move 173, black missed a chance to kill white's big group. Black should play at D11.
This implies white 172 is a blunder that should be at D11.
Even when putting it into the analysis engine of kg943, it evaluated the position as W+30-50 until I played it out until the end of the game when it swung in the opposite direction. I wouldn't have dared to post this otherwise, despite being fairly confident I'd checked all of the many variations (without AI).
I found this accidentally and manually, since I was confused as to why black resigned. It is true that in the final position white is unconditionally alive, by some tesujis that took me perhaps 1hour to figure out. It is surprisingly difficult for such a small space, but still a human level problem. Probably pro level.
Hint:
Curiously in the semeai in the lower right, black making a slightly bigger eye at N1 seems to increase their liberties from 5 to 7 since a white placement inside the eye requires throwing in 3 stones (due to the hane), which still gives black an eye so it seems white is forced to fill the outside liberties first (at T2 and T1), however, after throwing in the 3 stones, white can throw into the eyespace again, so it would actually only be 6 liberties.
Here is a simplified diagram to demonstrate why white can't live locally.
