A note on hyperspaces by closed sets with Vietoris topology

Abstract: For a topological space $X$, let $CL(X)$ be the set of all non-empty closed subset of $X$, and denote the set $CL(X)$ with the Vietoris topology by $(CL(X), \mathbb{V})$. In this paper, we mainly discuss the hyperspace $(CL(X), \mathbb{V})$ when $X$ is an infinite countable discrete space. As an application, we first prove that the hyperspace with the Vietoris topology on an infinite countable discrete space contains a closed copy of $n$-th power of Sorgenfrey line for each $n\in\mathbb{N}$. Then we investigate the tightness of the hyperspace $(CL(X), \mathbb{V})$, and prove that the tightness of $(CL(X), \mathbb{V})$ is equal to the set-tightness of $X$. Moreover, we extend some results about the generalized metric properties on the hyperspace $(CL(X), \mathbb{V})$. Finally, we give a characterization of $X$ such that $(CL(X), \mathbb{V})$ is a $\gamma$-space.