Sadaharu:
Modified some variations but seems like it's not reflected.

Fanfate:
Why doesn't work P18-S17-S16-T18-S19-R19-O18? ,

kovarex:
Since the problem is not simple, I added answers to bunch of wrong moves.

Sadaharu:
I think it's better to put another white stone outside, otherwise black can jump out after the answer's variation.