On centered local $\pi$-bases
Abstract
In 1967 Hajnal and Juh{\'a}sz showed that the cardinality of a first-countable Hausdorff space with the countable chain condition has cardinality at most , the cardinality of the real line. We give an improvement of this celebrated theorem by replacing ``first-countable" with the weaker condition ``each point has a countable centered local -base". Given a point in a topological space , a \emph{local} -\emph{base} at acts like a neighborhood base at except that may not be in any member of . A local -base has the \emph{finite intersection property} if any finite intersection of members of is nonempty. We call this type of local -base \emph{centered}. A centered local -base behaves even more like a neighborhood base in a sense. A space has the \emph{countable chain condition} if every family of pairwise disjoint open sets is countable. We also improve a theorem of Pospi{\v s}il from 1937 using centered local -bases. As is customary, examples are given to demonstrate these improvements are strict. Compact Hausdorff spaces are also explored in this connection, along with variations on the notion of a centered local -base.
Cite
@article{arxiv.2604.28092,
title = {On centered local $\pi$-bases},
author = {Nathan Carlson},
journal= {arXiv preprint arXiv:2604.28092},
year = {2026}
}
Comments
10 pages