Bąk, Judyta, and Andrzej Kucharski. “Topological Spaces With the Freese–Nation Property”. Annales Mathematicae Silesianae 33 (May 9, 2019): 41-54. Accessed May 18, 2024. https://journals.us.edu.pl/index.php/AMSIL/article/view/13649.