@article{IM_1988__93_2_143594,
     author = {D. Segal and F.J. Grunewald and G.C. Smith},
     title = {Subgroups of finite index in nilpotent groups.},
     journal = {Inventiones mathematicae},
     pages = {185--224},
     publisher = {mathdoc},
     volume = {93},
     number = {2},
     year = {1988},
     zbl = {0651.20040},
     url = {http://geodesic.mathdoc.fr/item/IM_1988__93_2_143594/}
}