English

A pseudometric on $\mathcal{M}(X,\mathscr{A})$ induced by a measure

General Topology 2025-05-27 v1

Abstract

For a probability measure space (X,A,μ)(X,\mathscr{A},\mu), we define a pseudometric δ\delta on the ring M(X,A)\mathcal{M}(X,\mathscr{A}) of real-valued measurable functions on XX as δ(f,g)=μ(XZ(fg))\delta(f,g)=\mu(X\setminus Z(f-g)) and denote the topological space induced by δ\delta as Mδ\mathcal{M}_\delta. We examine several topological properties, such as connectedness, compactness, Lindel\"{o}fness, separability and second countability of this pseudometric space. We realise that the space is connected if and only if μ\mu is a non-atomic measure and we explicitly describe the components in Mδ\mathcal{M}_\delta, for any choice of measure. We also deduce that Mδ\mathcal{M}_\delta is zero-dimensional if and only if μ\mu is purely atomic. We define μ\mu to be bounded away from zero, if every non-zero measurable set has measure greater than some constant. We establish several conditions equivalent to μ\mu being bounded away from zero. For instance, μ\mu is bounded away from zero if and only if Mδ\mathcal{M}_\delta is a locally compact space. We conclude this article by describing the structure of compact sets and Lindel\"{o}f sets in Mδ\mathcal{M}_\delta.

Keywords

Cite

@article{arxiv.2505.19780,
  title  = {A pseudometric on $\mathcal{M}(X,\mathscr{A})$ induced by a measure},
  author = {Amrita Dey},
  journal= {arXiv preprint arXiv:2505.19780},
  year   = {2025}
}
R2 v1 2026-07-01T02:39:02.428Z