@article{ELMA_1963__18_140778,
     author = {O. Giering},
     title = {\"Uber eine {Kennzeichnung} der gleichseitigen {Hyperbeln.}},
     journal = {Elemente der Mathematik},
     pages = {121--127},
     publisher = {mathdoc},
     volume = {18},
     year = {1963},
     zbl = {0119.36610},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1963__18_140778/}
}