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by Abram Demski 215 days ago | link | parent

Cool! I’m happy to see this written up finally. It’s been a big source of intuitions for me, so it’s good to see that the proof checks out.

A possible next step to all this is to try to specify proof-based DT agents which could play this game (or something similar) based on Löbian handshakes. (In fact, part of the original motivation was to try to bring the cooperative-oracle model closer to the Löb-based cooperation you can get in prisoner’s dilemma with visible source code.)

It’s unfortunate that you had to add the pareto-improvement condition to the cell rank. That part seems especially unlikely to drop out of a more general decision theory.

I think I see another serious complication:

Yes, not all points in \(C_{\vec{i}}\) attain the same utility, but for a sufficiently small ϵ, the cell is really small, and for any player, the utility over the cell is well-approximated by the utility attained at the middle point in the cell.

So, for any desired utility-approximation accuracy \(\delta\), you can choose \(\epsilon\) sufficiently small to achieve it. But, a pareto-optima in the set of middle points can be arbitrarily worse for some player than any pareto-optima of the full game; IE, taking the midpoints can hide arbitrarily large pareto improvements.

For example, suppose that \(\delta\)=0.001. A pareto optima of the midpoints might give the utility vector (2, 2, 3) for the three players. There could be another midpoint (100, 100, 2.9999999), very near where the true game contains a point (100, 100, 3).

So, it seems the pareto optimum of the game on midpoints which is found by the process in the post can be arbitrarily sub-optimal for all but one player, with no guarantee that this gets better as \(\epsilon\) shrinks.



by Alex Appel 215 days ago | Abram Demski likes this | link

If you drop the Pareto-improvement condition from the cell rank, and just have “everyone sorts things by their own utility”, then you won’t necessarily get a Pareto-optimal outcome (within the set of cell center-points), but you will at least get a point where there are no strict Pareto improvements (no points that leave everyone better off).

The difference between the two is… let’s say we’ve got a 2-player 2-move game that in utility-space, makes some sort of quadrilateral. If the top and right edges join at 90 degrees, the Pareto-frontier would be the point on the corner, and the set of “no strict Pareto improvements” would be the top and the right edges.

If that corner is obtuse, then both “Pareto frontier” and “no strict Pareto improvements” agree that both line edges are within the set, and if the corner is acute, then both “Pareto frontier” and “no strict Pareto improvements” agree that only the corner is within the set. It actually isn’t much of a difference, it only manifests when the utilities for a player are exactly equal, and is easily changed by a little bit of noise.

The utility-approximation issue you pointed out seems to be pointing towards the impossibility of guaranteeing limiting to a point on the Pareto frontier (when you make the cell size smaller and smaller), precisely because of that “this set is unstable under arbitrarily small noise” issue.

But, the “set of all points that have no strict Pareto improvements by more than \(\delta\) for all players”, ie, the \(\delta\)-fuzzed version of “set of points with no strict pareto improvement”, does seem to be robust against a little bit of noise, and doesn’t require the Pareto-improvement condition on everyone’s ranking of cells.

So I’m thinking that if that’s all we can attain (because of the complication you pointed out), then it lets us drop that inelegant Pareto-improvement condition.

I’ll work on the proof that for sufficiently small cell size \(\epsilon\), you can get an outcome within \(\delta\) of the set of “no strict Pareto improvements available”

Nice job spotting that flaw.

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