@article{GDZPPN00210542X, title = {Subgroups of finite index in nilpotent groups.}, journal = {Inventiones mathematicae}, volume = {93}, year = {1988}, pages = {185-224}, zbl = {0651.20040}, url = {http://dml.mathdoc.fr/item/GDZPPN00210542X} }
Segal, D.; Grunewald, F.J.; Smith, G.C. Subgroups of finite index in nilpotent groups.. Inventiones mathematicae, Tome 93 (1988) pp. 185-224. http://gdmltest.u-ga.fr/item/GDZPPN00210542X/