Noir:
B15 here should work...

kovarex:
Hello, this is the same problem as one from my collection, but here it contains less variations, mainly, it doesn't contain the refutation of the most obvious answer to white atare with the empty triangle. https://tsumego-hero.com/tsumegos/play/27473 So I went ahead, and just replaced this SGF with the SGF from my collection. I believe, that this is a good example of what we should do with the database cleanup later. We should have a technical means to keep these 2 problems still separated, but to keep their SGF and meta data shared .