terraform wrote:...I just saw a way to turn what I thought was seki into a possible kill. I'm still wondering if my sacrifice was worth it. The way I figure it in my latest musings, the center group was worth a little more than the side.
The ko at move 129 was large, so spotting it was good on your part, but you seem to have misunderstood its significance, and you misplayed the continuation. You had some trouble judging ko situations throughout the game, so spending some time analyzing this one would be a good exercise.
The important thing to realize about this particular ko is that it is a "flower-viewing" ko, which is a burden only for W. If B wins the ko, he captures the center stones, but if W wins the ko the center remains seki, so B loses nothing. Actually, the risk for W is much larger than this, since B should win the ko by capturing at S14 (instead of the game move P10). Please verify that this capture leaves the W center dead, with no need to play the actual capturing moves anytime soon.
Reading a little further, if W ignores the B capture at S14 (to make good on his ko threat for example), then B can capture again at S16. This last capture is huge, as it leaves the W side group dead, provided the B lower right corner is still alive. So really the only conceivable ko threats W has are threats against the lower right group.
B should patiently answer any real W ko threats in the corner, since he has no need to risk anything. The profit B would obtain just by getting two free moves somewhere else on the board exceeds the profit obtained by trading groups. In this game, the B corner is actually larger than the W center (exercise -- try counting the difference), so B turned a flower-viewing ko into a loss of points.
Finally, if you look closely, W really has no ko threats to kill the B corner. In the game, B captured the W center stones with move 133, but that move was basically a pass, since it was already too late for W to prevent this capture. If instead B captured at T7, the corner would be alive, and B would have captured the W center stones for free.