darius comments on The Curve of Capability - Less Wrong
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I'm confused or about to display my ignorance. When you write:
Are you saying that evaluating a Go position has exponential (time?) cost even on a nondeterministic machine? I thought that any given string of moves to the end of the game could be evaluated in polynomial (N^2?) time. I thought that the full set of possible strings of moves could be evaluated (naively) in exponential time on a deterministic machine and polynomial time on a nondeterministic machine - so I thought Go position evaluation would be in NP. I think you are saying that it is more costly than that. Are you saying that, and what am I getting wrong?
"Does this position win?" has a structure like "Is there a move such that, for each possible reply there is a move such that, for each possible reply... you win." -- where existential and universal quantifiers alternate in the nesting. In a SAT problem on the other hand you just have a nest of existentials. I don't know about Go specifically, but that's my understanding of the usual core difference between games and SAT.
Much appreciated! So the NP solution to SAT is basically an OR over all of the possible assignments of the variables, where here (or for alternating move games in general), we've got alternating ORs and ANDs on sequential moves.