@article{PORMA_1967__26_2_115014,
     author = {Spira, Robert},
     title = {Derived-set axioms for topological spaces},
     journal = {Portugaliae mathematica},
     pages = {165--167},
     publisher = {mathdoc},
     volume = {26},
     number = {2},
     year = {1967},
     mrnumber = {0251684},
     zbl = {0181.25501},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1967__26_2_115014/}
}