English

A generalization of the density zero ideal

General Topology 2020-07-20 v2

Abstract

Let F=(Fn)\mathscr{F}=(F_n) be a sequence of nonempty finite subsets of ω\omega such that limnFn=\lim_n |F_n|=\infty and define the ideal I(F):={Aω:AFn/Fn0 \mboxas n}.\mathcal{I}(\mathscr{F}):=\left\{A\subseteq \omega: |A\cap F_n|/|F_n|\to 0~\mbox{as}~n\to \infty \right\}. The case Fn={1,,n}F_n=\{1,\ldots,n\} corresponds to the classical case of density zero ideal. We show that I(F)\mathcal{I}(\mathscr{F}) is an analytic P-ideal but not FσF_{\sigma}. As a consequence, we show that the set of real bounded sequences which are I(F)\mathcal{I}(\mathscr{F})-convergent to 00 is not complemented in \ell_\infty.

Keywords

Cite

@article{arxiv.2005.12355,
  title  = {A generalization of the density zero ideal},
  author = {Sumit Som},
  journal= {arXiv preprint arXiv:2005.12355},
  year   = {2020}
}

Comments

3 pages

R2 v1 2026-06-23T15:48:09.171Z