English

Minimal Size of Basic Families

General Topology 2009-09-28 v1 Classical Analysis and ODEs

Abstract

A family \bfam\bfam of continuous real-valued functions on a space XX is said to be {\sl basic} if every fC(X)f \in C(X) can be represented f=i=1ngiϕif = \sum_{i=1}^n g_i \circ \phi_i for some ϕi\bfam\phi_i \in \bfam and giC(R)g_i \in C(\R) (i=1,...,ni=1, ..., n). Define \basic(X)=min{\bfam:\bfam\basic (X) = \min \{|\bfam| : \bfam is a basic family for X}X\}. If XX is separable metrizable XX then either XX is locally compact and finite dimensional, and \basic(X)<0\basic (X) < \aleph_0, or \basic(X)=c\basic (X) = \mathfrak{c}. If KK is compact and either w(K)w(K) (the minimal size of a basis for KK) has uncountable cofinality or KK has a discrete subset DD with D=w(K)|D|=w(K) then either KK is finite dimensional, and \basic(K)=\cof([w(K)]0,)\basic (K) = \cof ([w(K)]^{\aleph_0}, \subseteq), or \basic(K)=C(K)=w(K)0\basic (K) = |C(K)|=w(K)^{\aleph_0}.

Cite

@article{arxiv.0909.4563,
  title  = {Minimal Size of Basic Families},
  author = {Ziqin Feng and Paul Gartside},
  journal= {arXiv preprint arXiv:0909.4563},
  year   = {2009}
}
R2 v1 2026-06-21T13:50:17.670Z