@article{IM2_1967_1_5_a8,
     author = {A. L. Shmel'kin},
     title = {On free polynilpotent groups},
     journal = {Izvestiya. Mathematics },
     pages = {1065--1080},
     publisher = {mathdoc},
     volume = {1},
     number = {5},
     year = {1967},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1967_1_5_a8/}
}