EL-MONSEF, M. E. ABD, A. M. KOZAE, and A. A. ABO KHAORA. “ON FILTER EXPANSION OF TOPOLOGIES”. Tamkang Journal of Mathematics 25, no. 1 (March 1, 1994): 53–59. Accessed May 5, 2024. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/4425.