@article{DAN_1991_318_4_a5,
     author = {Yu. L. Ershov},
     title = {Projective $\Gamma$-groups},
     journal = {Doklady Akademii Nauk},
     pages = {798--801},
     publisher = {mathdoc},
     volume = {318},
     number = {4},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1991_318_4_a5/}
}