@article{AM2_1987__34_137222,
     author = {Walter Benz and Hubert Berens},
     title = {A contribution to a theorem of {Ulam} and {Mazur.}},
     journal = {Aequationes mathematicae},
     pages = {61--63},
     publisher = {mathdoc},
     volume = {34},
     year = {1987},
     zbl = {0651.46022},
     url = {http://geodesic.mathdoc.fr/item/AM2_1987__34_137222/}
}