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.
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.