@article{DAN_1969_188_5_a12,
     author = {I. D. Stupina},
     title = {Certain properties of $R$- and $R^c$-operations},
     journal = {Doklady Akademii Nauk},
     pages = {1010--1013},
     year = {1969},
     volume = {188},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1969_188_5_a12/}
}