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@article{PIM_1968_N_S_08_22_a22, author = {{\DJ}uro Kurepa}, title = {On {The} {Category} {Number} {Of} {Topological} {Spaces}}, journal = {Publications de l'Institut Math\'ematique}, pages = {149 }, publisher = {mathdoc}, volume = {_N_S_08}, number = {22}, year = {1968}, url = {http://geodesic.mathdoc.fr/item/PIM_1968_N_S_08_22_a22/} }
Đuro Kurepa. On The Category Number Of Topological Spaces. Publications de l'Institut Mathématique, _N_S_08 (1968) no. 22, p. 149 . http://geodesic.mathdoc.fr/item/PIM_1968_N_S_08_22_a22/