buddhata: Thanks for adding A1. To me, after C1, it seems like a ko, and at first I was confused but in the end the defender can live unconditionally exactly because of A1
GoDave89: @dtiger
It's true that A1 works, too.
Though to be fair it's a highly unnatural move and slightly worse than B2 (because B2 threatens to take at C1 - and in an actual game black might want to ignore the local situation for a bit) ^^
caranthir: Yeah, it gives the "attacker" the option to tenuki right away and make a more profitable sacrifice out of all the three stones; the "defender" will invest 3 moves, instead of 2 if B2 - or C1, which should be the best one - were played. In other words, attacker can decrease the value of A1 next to zero.
I added that, though, since all of the solutions expect taking the ko (at C1) at once really are suboptimal.
Thanks for adding A1. To me, after C1, it seems like a ko, and at first I was confused but in the end the defender can live unconditionally exactly because of A1