The Lower Central Series of a Join of Subnormal Subgroups. J.C. Lennox; D. Segal; S. Stonehewer — 1977 Mathematische Zeitschrift
Nilpotent Groups of Hirsch Length Six. D. Segal; F.J. Grunewald; L.S. Sterling — 1982 Mathematische Zeitschrift
Subgroups of finite index in nilpotent groups. D. Segal; F.J. Grunewald; G.C. Smith — 1988 Inventiones mathematicae