@article{SM_1972_16_3_a2,
     author = {A. A. Bovdi and I. I. Khripta},
     title = {Normal subgroups of the multiplicative group of a~ring},
     journal = {Sbornik. Mathematics},
     pages = {349--362},
     year = {1972},
     volume = {16},
     number = {3},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1972_16_3_a2/}
}