@article{MZ_1959__72_183596,
     author = {Eberhard Hopf},
     title = {Zur {Kennzeichnung} der {Euklidischen} {Norm.}},
     journal = {Mathematische Zeitschrift},
     pages = {76--81},
     publisher = {mathdoc},
     volume = {72},
     year = {1959},
     zbl = {0088.08503},
     url = {http://geodesic.mathdoc.fr/item/MZ_1959__72_183596/}
}