Wei Dai's argument was specifically against the Solomonoff prior, which assigns probability 0 to the existence of halting problem oracles. If you have an idea how to formulate another universal prior that would give such "impossible" things positive probability, but still sum to 1.0 over all hypotheses, then by all means let's hear it.
Yeah well it is certainly a good argument against that. The title of the thread is "is induction unformalizable" which point I'm unconvinced of.
If I were to formalize some kind of prior, I would probably use a lot of epsilons (since zero is not a probability); including an epsilon for "things I haven't thought up yet." On the other hand I'm not really an expert on any of these things so I imagine Wei Dai would be able to poke holes in anything I came up with anyway.
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