@article{SM_1974_23_4_a6,
     author = {L. A. Shemetkov},
     title = {Graduated formations of groups},
     journal = {Sbornik. Mathematics},
     pages = {593--611},
     publisher = {mathdoc},
     volume = {23},
     number = {4},
     year = {1974},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1974_23_4_a6/}
}