Chagrov, A. V. Kuratowski numbers. (Russian) Zbl 0532.54003 Primen. Funkts. Anal. Teor. Priblizh. 1982, 186-190 (1982). MSC: 54A05 Topological spaces and generalizations (closure spaces, etc.) 54A25 Cardinality properties (cardinal functions and inequalities, discrete subsets) PDF BibTeX XML OpenURL