@article{RSMUP_1977__58__1_0,
     author = {Messa, Kenneth},
     title = {A generalization of {Ulm} subgroups},
     journal = {Rendiconti del Seminario Matematico della Universit\`a di Padova},
     pages = {1--7},
     publisher = {Seminario Matematico of the University of Padua},
     volume = {58},
     year = {1977},
     mrnumber = {543124},
     zbl = {0417.16016},
     language = {en},
     url = {http://archive.numdam.org/item/RSMUP_1977__58__1_0/}
}