MendelSchmiedekamp comments on Money pumping: the axiomatic approach - Less Wrong

12 Post author: Stuart_Armstrong 05 November 2009 11:23AM

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Comment author: MendelSchmiedekamp 10 November 2009 04:38:19PM 1 point [-]

Note, Independence II does not imply Independence, without using at least the consistency axiom.

Comment author: Stuart_Armstrong 11 November 2009 11:27:15AM 1 point [-]

The contrapositive of independence II is:

For all A, B, C, D and p, if A ≤ B and C ≤ D, then pA + (1-p)C ≤ pB + (1-p)D.

If we now take C and D to be the same lottery, we get independence, as long as C ≤ C. Now, given completeness, C ≤ C is always true (because at least one of C=C, C<C or C>C must be true, and thus we can always get C ≤ C, -- switching C with C if needed!).

So we don't need consistency, we need a weak form of completeness, in which every lottery can be at least compared with itself.

Comment author: RobinZ 10 November 2009 04:54:21PM 1 point [-]

Transitivity and Continuity are unnecessary, however.

Comment author: MendelSchmiedekamp 10 November 2009 05:24:09PM 0 points [-]

That is my reading of it too. I know Stuart is putting forward analytic results here, I was concerned that this one was not correctly represented.