Elostath, Lubna, and Hisham Mahdi. “Somewhere Dense on Upper Bounded \(T_{0}\)-Alexandroff Spaces”. Journal of Advanced Studies in Topology 11, no. 1-2 (September 21, 2020): 6–15. Accessed June 16, 2021. https://m-sciences.com/?journal=jast&page=article&op=view&path[]=1636.