We construct a consistent example of a topological space Y=X∪{∞}Y=X∪{∞} such that: 1) YY is regular. 2) Every GδGδ subset of YY is open. 3) The point ∞∞ is not isolated, but it is not in the closure of any discrete subset of XX.
生成讲解博客的中文版本
生成AI智能校验的中文版本