and is the best play for both players, with White taking the ko first.
Refer to Tripod Group with Extra Leg for more details.
Paul Pogonyshev: this move looks fine. It threatens the stones.
lavalyn: Not really. See below.
Paul Pogonyshev: Yes, it's not as fine as it looked :)
If White doesn't capture again, she loses and the second eye. So she has to play at . Black threatens with . White has no option other than to connect with and then Black captures ko with , forcing White to connect with . It's over now: Black places a stone at a, killing White.
Of course, lavalyn's alternative way of playing (shown below) is correct too.
lavalyn claims the solution above fails:
Paul Pogonyshev: it's night time and I am tired, but as far as I can see, White is alive with three eyes here. What's wrong?
Paul Pogonyshev: This is what I believe is on the board after the sixth move. Black can't capture at a (ko). Next move White captures at b, or if Black has played there, at c and lives with three eyes. Or not?
Paul Pogonyshev: OK, I knew what ko is ;) I merely misunderstood the task, thinking it was to kill White.
For more information, reference the Tripod Group with Extra Leg.