Life In 19x19

Uberdude wrote:Good question Leon, and nice spot of g1 (which I didn't see during the game). Here's my idea:
- the ko is not just about life/death of black/white in the corner, but also about the eyes of the outside black group. Working backwards:
- white could have simply answered black 145 at c8 and black's corner would be dead rather than the approach ko it became in the game (for which white got a few moves to build his centre), but then black would get d6 in sente which builds some handy eyes in e6 area, and then presumably play something in the centre.
- Given that white didn't answer, and if we make the assumption this was a reasonable decision of Ke Jie and not just misguided human fighting spirit (which is not as simple as does bot agree: a bot may be confident it can play out the half point win with c8 answer whereas Ke might see that as too uncertain and actually prefer a more complicated game where he can demonstrate his superior skill), then that explains Kim's earlier decision to give up on the ko (for now) and take the q12 profit and attempt to force from the outside with d7.
- so if white plays g1 then he loses 1 point as eventually he'll capture the stones anyway when black fills dame, black still gets the d6 forcing move for eyes, and because of the double ko infinite threats black can win any other ko such as answering e9 at e8 which means that group is practically alive in sente and he can then turn to the centre. So white played the atari because he wanted to make black's outside group weaker and then if he wins the ko it's in big trouble without d6 sente (even more so after white f8)
- so Ke makes the ko bigger, thus Kim feels he can't answer the q10 threat (which makes Ke's previous centre moves during ko better as now black's group is weak so he can't be aggressive in the centre), and also creates weakness in g8 connection which makes the cut for desserts we saw later in game.