Characterizations of open and semi-open maps of compact Hausdorff spaces by induced maps

Abstract

Let $f\colon X\rightarrow Y$ be a continuous surjection of compact Hausdorff spaces. By $$f_*\colon\mathfrak{M}(X)\rightarrow\mathfrak{M}(Y),\ \mu\mapsto \mu\circ f^{-1} \quad{\rm and}\quad 2^f\colon2^X\rightarrow2^Y,\ A\mapsto f[A]$$ we denote the induced continuous surjections on the probability measure spaces and hyperspaces, respectively. In this paper we mainly show the following facts: (1) If $f_*$ is semi-open, then $f$ is semi-open. (2) If $f$ is semi-open densely open, then $f_*$ is semi-open densely open. (3) $f$ is open iff $2^f$ is open. (4) $f$ is semi-open iff $2^f$ is semi-open. (5) $f$ is irreducible iff $2^f$ is irreducible.