English

Counting continua

General Topology 2025-12-17 v1

Abstract

For infinite cardinals κ,λ\kappa,\lambda let C(κ,λ)C(\kappa,\lambda) denote the class of all compact Hausdorff spaces of weight κ\kappa and size λ\lambda. So C(κ,λ)=C(\kappa,\lambda)=\emptyset if κ>λ\kappa>\lambda or λ>2κ\lambda>2^\kappa. If F is a class of pairwise non-homeomorphic spaces in C(κ,λ)C(\kappa,\lambda) then F is a set of size not greater than 2κ2^\kappa. For every infinite cardinal κ\kappa we construct 2κ2^\kappa pairwise non-embeddable pathwise connected spaces in C(κ,λ)C(\kappa,\lambda) for λ=max{20,κ}\lambda=\max\{2^{\aleph_0},\kappa\} and for λ=explog(κ+)\lambda=\exp\log(\kappa^+). (If κ\kappa is a strong limit then explog(κ+)=2κ\exp\log(\kappa^+)=2^\kappa.) Additionally, for all infinite cardinals κ,μ\kappa,\mu with μκ\mu\leq\kappa we construct 2κ2^\kappa pairwise non-embeddable connected spaces in C(κ,κμ)C(\kappa,\kappa^\mu). Furthermore, for κ=λ=2θ\kappa=\lambda=2^\theta with arbitrary θ\theta and for certain other pairs κ,λ\kappa,\lambda we construct 2κ2^{\kappa} pairwise non-embeddable connected, linearly ordered spaces XC(κ,λ)X\in C(\kappa,\lambda) such that YC(κ,λ)Y\in C(\kappa,\lambda) whenever YY is an infinite compact and connected subspace of XX. On the other hand we prove that there is no space XX with this property if λ\lambda is of countable cofinality and either κ=λ\kappa=\lambda or λ\lambda is a strong limit.

Keywords

Cite

@article{arxiv.2512.14371,
  title  = {Counting continua},
  author = {Gerald Kuba},
  journal= {arXiv preprint arXiv:2512.14371},
  year   = {2025}
}