posetcay:
Marked B18 as wrong because it leads to ko as Hrewsahgs said, B17 is the only move that leads to clean kill.

Hrewsahgs:
Would you be willing to add the strongest resistance to the diagram when S3's the first move then? I just can't seem to find it, and this line only has the clean kill variation.

Hrewsahgs:
This position kills directly, though?

Hrewsahgs:
I don't think this works. A17 here instead of C18 should allow white to at least make a ko.