@article{DAN_1977_237_2_a4,
     author = {I. I. Parovichenko},
     title = {On the structure of a class of set-theoretic operations},
     journal = {Doklady Akademii Nauk},
     pages = {272--275},
     publisher = {mathdoc},
     volume = {237},
     number = {2},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1977_237_2_a4/}
}