@article{MZ_1975__141_172173,
     author = {J\"urgen Elsner},
     title = {Zum },
     journal = {Mathematische Zeitschrift},
     pages = {265--278},
     publisher = {mathdoc},
     volume = {141},
     year = {1975},
     zbl = {0283.28006},
     url = {http://geodesic.mathdoc.fr/item/MZ_1975__141_172173/}
}