English

Tauberian theorems for ordinary convergence

Functional Analysis 2020-12-08 v1 General Topology

Abstract

We show that a real sequence xx is convergent if and only if there exist a regular matrix AA and an FσδF_{\sigma\delta}-ideal I\mathcal{I} on N\mathbf{N} such that the set of subsequences yy of xx for which AyAy is I\mathcal{I}-convergent is of the second Baire category. This includes the cases where I\mathcal{I} is the ideal of asymptotic density zero sets, the ideal of Banach density zero sets, and the ideal of finite sets. The latter recovers an old result given by Keogh and Petersen in [J. London Math. Soc. \textbf{33} (1958), 121--123]. Our proofs are of a different nature and rely on recent results in the context of I\mathcal{I}-Baire classes and filter games. As application, we obtain a stronger version of the classical Steinhaus' theorem: for each regular matrix AA, there exists a {0,1}\{0,1\}-valued sequence xx such that AxAx is not statistically convergent.

Keywords

Cite

@article{arxiv.2012.03311,
  title  = {Tauberian theorems for ordinary convergence},
  author = {Paolo Leonetti},
  journal= {arXiv preprint arXiv:2012.03311},
  year   = {2020}
}

Comments

10 pp, comments are welcome

R2 v1 2026-06-23T20:45:50.709Z