Izrafel: Why does the attacker need to play S16? Even if the defender takes the S16 point himself the attacker can negate the second eye by playing at T16. There is no way to make 2 eyes in the Q,R,S19 zone.
Sadaharu: It is seki if white plays B16. I suggest you read up on Seki: https://senseis.xmp.net/?Seki
It is seki if white plays B16. I suggest you read up on Seki: https://senseis.xmp.net/?Seki