PhilGoetz comments on A simple counterexample to deBlanc 2007? - Less Wrong

3 Post author: PhilGoetz 30 May 2011 05:09AM

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Comment author: PhilGoetz 30 May 2011 06:03:35PM *  0 points [-]

This is supposed to be a counterexample. A counterexample means you are allowed to select any possible case. This is one possible case. I am not "replacing S_I by something completely different." I am choosing one possible S_I. If you don't like my choice of S_I, you need to show that it is not a possible case. That would include showing that I have chosen an S_I that is inconsistent with my earlier choices. Try to do that.

If I had specified the set of observations I, then also specified S_I in a way not determined by I, then you could make that argument. As I have not specified I, you need to show that my choice of S_I is inconsistent with any possible set I in order to make the argument you're trying to make.

Comment author: endoself 30 May 2011 07:13:29PM *  3 points [-]

Let J be the constant set that I is currently equal to. Your agent's set of hypotheses then does not contain the computable function f(k) =

  • (2(1-1/2^k))^4 for all K in J

  • -k for all K not in J

By construction, this hypothesis must be compatible with the known input-output pairs, since it is indistinguishable from your f_4 given the observations in J. S_I must therefore contain f iff it contains f_4. Your S_I does not satisfy this, so it is not a counterexample.

Comment author: PhilGoetz 30 May 2011 07:49:44PM *  3 points [-]

I think you're right. You may have unravelled my counterexample. Tentative congratulations!

I now get to eat a piece of chocolate, as a reward for being proven wrong.

Comment author: Morendil 31 May 2011 08:33:18AM 0 points [-]

Suggestion: treat yourself to a second piece of chocolate and add an ETA at the top of the post - the parent comment is buried too deeply in the thread, for informational purposes.

Comment author: RichardKennaway 31 May 2011 08:21:59AM *  0 points [-]

As I have not specified I, you need to show that my choice of S_I is inconsistent with any possible set I in order to make the argument you're trying to make.

In the original paper, S_I is determined by I. There is no I for which your set S_I is the set defined in the paper. It really is as simple as that.