@article{MZ_1965__90_170463,
     author = {Gilbert Helmberg},
     title = {\"Uber rein dissipative {Transformationen.}},
     journal = {Mathematische Zeitschrift},
     pages = {41--53},
     year = {1965},
     volume = {90},
     zbl = {0178.38701},
     url = {http://geodesic.mathdoc.fr/item/MZ_1965__90_170463/}
}