کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
4658502 | 1633101 | 2014 | 13 صفحه PDF | دانلود رایگان |
A space X is said to be star-Menger (resp., strongly star-Menger) if for each sequence {Un:n∈ω}{Un:n∈ω} of open covers of X , there are finite subfamilies Vn⊂UnVn⊂Un (resp., finite subsets Fn⊂XFn⊂X) such that {St(⋃Vn,Un):n∈ω}{St(⋃Vn,Un):n∈ω} (resp., {St(Fn,Un):n∈ω}{St(Fn,Un):n∈ω}) is a cover of X. These star versions of the Menger property were first introduced and studied in Kočinac [14] and [15]. In this paper, answering Song's question, we show that the extent of a regular strongly star-Menger space cannot exceed the continuum cc. Star-Menger Pixley–Roy hyperspaces PR(X)PR(X) are also investigated. We show that if a space X is regular and PR(X)PR(X) is star-Menger, then the cardinality of X is less than cc and every finite power of X is Menger.
Journal: Topology and its Applications - Volume 176, 1 October 2014, Pages 22–34