Characterizing function spaces which have the property (B) of Banakh

TL;DR

This paper characterizes when the function space $C_p(X)$ with pointwise convergence topology has property (B) of Banakh, linking it to a specific property $( abla)$ of the underlying space $X$, and provides related results for the compact-open topology.

Contribution

It establishes a precise criterion involving property $( abla)$ for $C_p(X)$ to have property (B), and offers new examples and characterizations related to this property.

Findings

Characterization of property (B) for $C_p(X)$ in terms of property $( abla)$ of $X$.

Equivalent conditions for the compact-open topology on $C(X)$.

Examples of spaces with finite bounded subsets but lacking property $( abla)$.

Abstract

A topological space $Y$ has the property (B) of Banakh if there is a countable family $\{A_n:n\in \mathbb{N}\}$ of closed nowhere dense subsets of $Y$ absorbing all compact subsets of $Y$. In this note we show that the space $C_p(X)$ of continuous real-valued functions on a Tychonoff space $X$ with the topology of pointwise convergence, fails to satisfy the property (B) if and only if the space $X$ has the following property $(\kappa)$: every sequence of disjoint finite subsets of $X$ has a subsequence with point--finite open expansion. Additionally, we provide an analogous characterization for the compact--open topology on $C(X)$. Finally, we give examples of Tychonoff spaces $X$ whose all bounded subsets are finite, yet $X$ fails to have the property $(\kappa)$. This answers a question of Tkachuk.