@article{DAN_1974_216_1_a4,
     author = {B. A. Efimov and G. I. Chertanov},
     title = {On some operations on classes of topological spaces},
     journal = {Doklady Akademii Nauk},
     pages = {25--27},
     publisher = {mathdoc},
     volume = {216},
     number = {1},
     year = {1974},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1974_216_1_a4/}
}