English

Large sets avoiding affine copies of infinite sequences

Classical Analysis and ODEs 2022-04-28 v1 Metric Geometry

Abstract

A conjecture of Erd\H{o}s states that for any infinite set ARA \subseteq \mathbb R, there exists ERE \subseteq \mathbb R of positive Lebesgue measure that does not contain any nontrivial affine copy of AA. The conjecture remains open for most fast-decaying sequences, including the geometric sequence A={2k:k1}A = \{2^{-k} : k \geq 1\}. In this article, we consider infinite decreasing sequences A={ak:k1}A = \{a_k: k \geq 1\} in R{\mathbb R} that converge to zero at a prescribed rate; namely log(an/an+1)=eφ(n)\log (a_n/a_{n+1}) = e^{\varphi(n)} , where φ(n)/n0\varphi(n)/n\to 0 as nn\to\infty. This condition is satisfied by sequences whose logarithm has polynomial decay, and in particular by the geometric sequence. For any such sequence AA, we construct a Borel set OR{\mathcal O}\subseteq \mathbb R of Hausdorff dimension 1, but Lebesgue measure zero, that avoids all nontrivial affine copies of A{0}A\cup\{0\}.

Keywords

Cite

@article{arxiv.2204.12720,
  title  = {Large sets avoiding affine copies of infinite sequences},
  author = {Angel Cruz and Chun-Kit Lai and Malabika Pramanik},
  journal= {arXiv preprint arXiv:2204.12720},
  year   = {2022}
}

Comments

arXiv admin note: substantial text overlap with arXiv:2001.02395

R2 v1 2026-06-24T10:59:50.664Z