@article{DAN_1967_172_1_a6,
     author = {V. T. Nagrebetskii},
     title = {Invariant coverings of subgroups},
     journal = {Doklady Akademii Nauk},
     pages = {30--32},
     year = {1967},
     volume = {172},
     number = {1},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1967_172_1_a6/}
}