Bridging Computational Notions of Depth: Working Towards the Proof of Lemma 3

Working towards the proof of Lemma 3, we first establish the following result.


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Abstract and 1 Introduction

2 Background

3 On the slow growth law

4 Members of Deep Π0 1 classes

5 Strong depth is Negligible

6 Variants of Strong Depth

References

References

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Appendix A. Proof of Lemma 3

Working towards the proof of Lemma 3, we first establish the following result.

\ \

\ \ We thus have the identity

\ \

\ \ Then by our initial assumption on t and t′, we have

\ \

\ \ The lemma follows by taking the negative logarithm of this inequality

\ We can now prove Lemma 3. The (i)→(ii) implication is immediate. For the (ii)→(i) implication, suppose X is a sequence and h a computable increasing function such that

\ \

\ \ for any time bound t. If k ∈ [h(n), h(n + 1)), we have

\ \

\ \ We now apply the previous lemma with σ = X↾h(n), τ = X↾[h(n), k) and E the map such that, on input ρ, checks whether ρ has length h(n) for some n and if so returns all strings whose length is between 0 and h(n + 1) − h(n) (otherwise E(ρ) is empty). The lemma gives us a computable time bound s such that

\ \

\ \ This being true for all n and all k ∈ [h(n), h(n + 1)), we have

\ \

\ \ and thus X is order-deep.

\ Finally, the (ii)↔(iii) equivalence can be established using Lemma 1(iii) and Theorem 2.

\

:::info This paper is available on arxiv under CC BY 4.0 DEED license.

:::

:::info Authors:

(1) Laurent Bienvenu;

(2) Christopher P. Porter.

:::

Photo by Matt Hardy on Unsplash


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