@article{MZ_1964__86_170329,
     author = {H. Neumann and B.H. Neumann and G. Baumslag},
     title = {On varieties generated by a finitely generated group.},
     journal = {Mathematische Zeitschrift},
     pages = {93--122},
     year = {1964},
     volume = {86},
     zbl = {0125.01402},
     url = {http://geodesic.mathdoc.fr/item/MZ_1964__86_170329/}
}