1 Answers
In mathematics, a topological space X {\displaystyle X} is a D-space if for any family { U x : x ∈ X } {\displaystyle \{U_{x}:x\in X\}} of open sets such that x ∈ U x {\displaystyle x\in U_{x}} for all points x ∈ X {\displaystyle x\in X} , there is a closed discrete subset D {\displaystyle D} of the space X {\displaystyle X} such that ⋃ x ∈ D U x = X {\displaystyle \bigcup _{x\in D}U_{x}=X}.
4 views
Answered