Actually, the go endgame isn't just "tidying up the boundaries": I can just invade your territory. If you play right my invasion will eventually die, it was unjustified, so humans do not do it. (Except: if it is a pro versus me, he'd likely do an unjustified invasion anyhow because he'd guess I'd often be too dumb to respond correctly.) But my point is, all those invasions and refutations always are there like a sleeping volcano beneath the surface, strong humans just never play them and their refutations, since it'd be a waste of time; they just agree to end the game. It doesn't hurt your score in chinese rules if you play an unjustified invasion which gets killed, so in principle you should try it. What that also means: the part of alphago's training that was based on strong human games, contained zero examples of that stuff! So maybe if Lee Sedol tried it, alphago would mess up. I guarantee you, it has a higher probability of working than resigning. Also, presumably alphago usually works well, but even its designers really do not understand why and cannot guarantee it will not do something crazy next move. It really is an AI in the sense that nobody understands what it is thinking and there is no way it could explain it to us. Unlike, say, today's strongest chess programs, which I feel I pretty much totally understand -- they have human designed evaluation functions with some parameters tuned by fairly crude automated methods, but the whole evaluation function is something a human understands. That again, means if Lee Sedol took more of a software tester attitude, it could pay. Anyhow, LS has been rocked! There was a little press interview with LS after, and he looked a bit like he might break into tears. He said he just could not believe the machine could beat him, and even when LS felt he was behind, he still figured it was just a matter of time before machine would find a way to blow it. :) -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)