English

Dense families of countable sets below $c$

Logic 2010-03-15 v1 General Topology

Abstract

We show that it is consistent that the continuum is as large as you wish, and for each uncountable cardinal κ\kappa below the continuum, there are a subset TT of the reals and a family AA of countable subsets of TT such that (1) both TT and AA have cardinality κ\kappa, (2) aˉT=κ|\bar{a}\cap T|=\kappa for each aAa\in A, (3) for each uncountable subset of TT contains some elements of AA, and so (i) there is an almost disjoint family of subsets of the reals with size and chromatic number κ\kappa, (ii) there is a locally compact, locally countable T2T_2 space with cardinality spectrum {ω,κ}\{\omega,\kappa\}.

Keywords

Cite

@article{arxiv.1003.2496,
  title  = {Dense families of countable sets below $c$},
  author = {Lajos Soukup},
  journal= {arXiv preprint arXiv:1003.2496},
  year   = {2010}
}
R2 v1 2026-06-21T14:57:03.944Z