English

On a topological Erd\H{o}s similarity problem

Classical Analysis and ODEs 2022-11-01 v3 Metric Geometry

Abstract

A pattern is called universal in another collection of sets, when every set in the collection contains some linear and translated copy of the original pattern. Paul Erd\H{o}s proposed a conjecture that no infinite set is universal in the collection of sets with positive measure. This paper explores an analogous problem in the topological setting. Instead of sets with positive measure, we investigate the collection of dense GδG_{\delta} sets and in the collection of generic sets (dense GδG_{\delta} and complement has Lebesgue measure zero). We refer to such pattern as topologically universal and generically universal respectively. It is easy to show that any countable set is topologically universal, while any set containing an interior cannot be topologically universal. In this paper, we will show that Cantor sets on Rd{\mathbb R}^d are not topologically universal and Cantor sets with positive Newhouse thickness on R1{\mathbb R}^1 are not generically universal. This gives a positive partial answer to a question by Svetic concerning the Erd\H{o}s similarity problem on Cantor sets. Moreover, we also obtain a higher dimensional generalization of the generic universality problem.

Cite

@article{arxiv.2207.03077,
  title  = {On a topological Erd\H{o}s similarity problem},
  author = {John Gallagher and Chun-Kit Lai and Eric Weber},
  journal= {arXiv preprint arXiv:2207.03077},
  year   = {2022}
}

Comments

Final Version. Referee comments incorporated

R2 v1 2026-06-24T12:16:47.505Z