@article{MZ_1970__118_171451,
     author = {Terence E. Stanley},
     title = {Generalizations of the {Classes} of {Nilpotent} and {Hypercentral} {Groups.}},
     journal = {Mathematische Zeitschrift},
     pages = {180--190},
     year = {1970},
     volume = {118},
     zbl = {0194.03603},
     url = {http://geodesic.mathdoc.fr/item/MZ_1970__118_171451/}
}