English

Small uncountable cardinals in large-scale topology

Logic 2021-10-19 v7 Combinatorics

Abstract

In this paper we are interested in finding and evaluating cardinal characteristics of the continuum that appear in large-scale topology, usually as the smallest weights of coarse structures that belong to certain classes (indiscrete, inseparated, large) of finitary or locally finite coarse structures on ω\omega. Besides well-known cardinals b,d,c\mathfrak b,\mathfrak d,\mathfrak c we shall encounter two new cardinals Δ\mathsf \Delta and Σ\mathsf \Sigma, defined as the smallest weight of a finitary coarse structure on ω\omega which contains no discrete subspaces and no asymptotically separated sets, respectively. We prove that max{b,s,cov(N)}ΔΣnon(M)\max\{\mathfrak b,\mathfrak s,\mathrm{cov}(\mathcal N)\}\le\mathsf \Delta\le\mathsf \Sigma\le\mathrm{non}(\mathcal M), but we do not know if the cardinals Δ,Σ,non(M)\mathsf \Delta,\mathsf \Sigma,\mathrm{non}(\mathcal M) can be separated in suitable models of ZFC.

Keywords

Cite

@article{arxiv.2002.08800,
  title  = {Small uncountable cardinals in large-scale topology},
  author = {Taras Banakh},
  journal= {arXiv preprint arXiv:2002.08800},
  year   = {2021}
}

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37 pages