@article{SM_1968_5_3_a7,
     author = {A. Yu. Ol'shanskii},
     title = {On a problem of {Hanna} {Neumann}},
     journal = {Sbornik. Mathematics},
     pages = {429--432},
     year = {1968},
     volume = {5},
     number = {3},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1968_5_3_a7/}
}