Godzilla0: Hello, the shape isn't a bulky five because if black totally surround white after the correct sequence there is an atari on the white stones. In this case, if white capture, it provides a dead shape :)
caranthir: If I understood correctly you are talking about the right thing. The trick in the correct solution is to force a bulky five which also encloses an eye.
Markus: @Alberto: Your sequence (s18t18s17) provides a bulky five, true. But not good enough. -> Unconditionally alive, at least with seki
caranthir: [Farkas: Actually, it is not a bulky five.] To be accurate, it is a bulky five, but does not result in almost-filling the space with a bulky five. The correct solution where we enclose an eye with the shape achieves just that.
One of them makes seki while the other one kills.