@article{MAN_1977__229_163024,
     author = {Bruno Zimmermann},
     title = {Eine {Verallgemeinerung} der {Formel} von {Riemann-Hurwitz.}},
     journal = {Mathematische Annalen},
     pages = {279--288},
     publisher = {mathdoc},
     volume = {229},
     year = {1977},
     zbl = {0342.20025},
     url = {http://geodesic.mathdoc.fr/item/MAN_1977__229_163024/}
}