1.Reflective oracles as a solution to the converse Lawvere problem
post by Sam Eisenstat 523 days ago | Alex Mennen, Alex Appel, Vadim Kosoy, Abram Demski, Jessica Taylor, Scott Garrabrant and Vladimir Slepnev like this | discuss

1 Introduction

Before the work of Turing, one could justifiably be skeptical of the idea of a universal computable function. After all, there is no computable function $$f\colon\mathbb{N}\times\mathbb{N}\to\mathbb{N}$$ such that for all computable $$g\colon\mathbb{N}\to\mathbb{N}$$ there is some index $$i_{g}$$ such that $$f\left(i_{g},n\right)=g\left(n\right)$$ for all $$n$$. If there were, we could pick $$g\left(n\right)=f\left(n,n\right)+1$$, and then $g\left(i_{g}\right)=f\left(i_{g},i_{g}\right)+1=g\left(i_{g}\right)+1,$ a contradiction. Of course, universal Turing machines don’t run into this obstacle; as Gödel put it, “By a kind of miracle it is not necessary to distinguish orders, and the diagonal procedure does not lead outside the defined notion.” [1]

The miracle of Turing machines is that there is a partial computable function $$f\colon\mathbb{N}\times\mathbb{N}\to\mathbb{N}\cup\left\{ \bot\right\}$$ such that for all partial computable $$g\colon\mathbb{N}\to\mathbb{N}\cup\left\{ \bot\right\}$$ there is an index $$i$$ such that $$f\left(i,n\right)=g\left(n\right)$$ for all $$n$$. Here, we look at a different “miracle”, that of reflective oracles [2,3]. As we will see in Theorem 1, given a reflective oracle $$O$$, there is a (stochastic) $$O$$-computable function $$f\colon\mathbb{N}\times\mathbb{N}\to\left\{ 0,1\right\}$$ such that for any (stochastic) $$O$$-computable function $$g\colon\mathbb{N}\to\left\{ 0,1\right\}$$, there is some index $$i$$ such that $$f\left(i,n\right)$$ and $$g\left(n\right)$$ have the same distribution for all $$n$$. This existence theorem seems to skirt even closer to the contradiction mentioned above.

We use this idea to answer “in spirit” the converse Lawvere problem posed in [4]. These methods also generalize to prove a similar analogue of the ubiquitous converse Lawvere problem from [5]. The original questions, stated in terms of topology, remain open, but I find that the model proposed here, using computability, is equally satisfying from the point of view of studying reflective agents. Those references can be consulted for more motivation on these problems from the perspective of reflective agency.

Section 3 proves the main lemma, and proves the converse Lawvere theorem for reflective oracles. In section 4, we use that to give a (circular) proof of Brouwer’s fixed point theorem, as mentioned in [4]. In section 5, we prove the ubiquitous converse Lawvere theorem for reflective oracles.

2.Logical inductor limits are dense under pointwise convergence
post by Sam Eisenstat 929 days ago | Abram Demski, Patrick LaVictoire, Scott Garrabrant and Tsvi Benson-Tilsen like this | discuss

Logical inductors [1] are very complex objects, and even their limits are hard to get a handle on. In this post, I investigate the topological properties of the set of all limits of logical inductors.

3.A Counterexample to an Informal Conjecture on Proof Length and Logical Counterfactuals
post by Sam Eisenstat 1376 days ago | Jim Babcock, Abram Demski, Patrick LaVictoire and Scott Garrabrant like this | 1 comment

### NEW DISCUSSION POSTS

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There should be a chat icon
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There is a replacement for
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This seems like a hack. The
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After thinking some more,
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Yes, I think that we're
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To first approximation, a
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Actually, I *am* including
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> Well, we could give up on
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