@article{DAN_1957_115_5_a3,
     author = {I. I. Parovichenko},
     title = {Certain special classes of topological spaces and $\delta s$-operations},
     journal = {Doklady Akademii Nauk},
     pages = {866--868},
     publisher = {mathdoc},
     volume = {115},
     number = {5},
     year = {1957},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1957_115_5_a3/}
}