@article{IM2_1978_12_3_a4,
     author = {V. G. Kanovei},
     title = {On the nonemptiness of classes in axiomatic set theory},
     journal = {Izvestiya. Mathematics },
     pages = {507--535},
     publisher = {mathdoc},
     volume = {12},
     number = {3},
     year = {1978},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1978_12_3_a4/}
}