English

Topological spaces compact with respect to a set of filters

General Topology 2016-08-30 v2

Abstract

If P\mathcal P is a family of filters over some set II, a topological space XX is \emph{sequencewise P\mathcal P-\brfrt compact} if, for every II-indexed sequence of elements of XX, there is FPF \in \mathcal P such that the sequence has an FF-limit point. Countable compactness, sequential compactness, initial κ\kappa-compactness, [λ,μ][ \lambda ,\mu]-compactness, the Menger and Rothberger properties can all be expressed in terms of sequencewise P\mathcal P-compactness, for appropriate choices of P\mathcal P. We show that sequencewise P\mathcal P-compactness is preserved under taking products if and only if there is a filter FPF \in \mathcal P such that sequencewise P\mathcal P-compactness is equivalent to FF-compactness. If this is the case, and there exists a sequencewise P\mathcal P-compact T1T_1 topological space with more than one point, then FF is necessarily an ultrafilter. The particular cases of sequential compactness and of [λ,μ][ \lambda ,\mu]-compactness are analyzed in detail.

Keywords

Cite

@article{arxiv.1210.2120,
  title  = {Topological spaces compact with respect to a set of filters},
  author = {Paolo Lipparini},
  journal= {arXiv preprint arXiv:1210.2120},
  year   = {2016}
}

Comments

v.2, some improvements, divided into sections