English

Suprema of continuous functions on connected spaces

General Topology 2016-02-23 v1

Abstract

Let KK be a compact Hausdorff space and let (fn)nN(f_n)_{n\in \N} be a pairwise disjoint sequence of continuous functions from KK into [0,1][0,1]. We say that a compact space LL \emph{adds supremum} of (fn)nN(f_n)_{n\in \N} in KK if there exists a continuous surjection π:LK\pi:L\longrightarrow K such that there exists sup{fnπ:nN}sup\{f_n\circ\pi:n\in \N\} in C(L)C(L). Moreover, we expect that LL preserves suprema of disjoint continuous functions which already existed in C(K)C(K). Namely, if sup{gn:nN}sup\{g_n:n\in \N\} exists in C(K)C(K), we must have sup{gnπ:nN}sup\{g_n\circ\pi:n\in \N\} in C(L)C(L). This paper studies the preservation of connectedness in extensions by continuous functions -- a technique developed by Piotr Koszmider to add suprema of continuous functions on Hausdorff connected compact spaces -- proving the following results: (1) If KK is a metrizable and locally connected compactum, then any extension of KK by continuous functions is connected (but it may be not locally connected). (2) There exists a disconnected extension of a metrizable connected compactum KK. (3) For any metrizable compactum KK there exists a disconnected LL which is obtained from KK by finitely many extensions by continuous functions.

Keywords

Cite

@article{arxiv.1602.06891,
  title  = {Suprema of continuous functions on connected spaces},
  author = {André Santoleri Villa Barbeiro and Rogério Augusto dos Santos Fajardo},
  journal= {arXiv preprint arXiv:1602.06891},
  year   = {2016}
}
R2 v1 2026-06-22T12:55:20.427Z