@article{DAN_1971_201_1_a9,
     author = {I. I. Parovichenko},
     title = {Set-theoretic operations},
     journal = {Doklady Akademii Nauk},
     pages = {40--43},
     publisher = {mathdoc},
     volume = {201},
     number = {1},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1971_201_1_a9/}
}