@article{CMH_1933__5_138592,
     author = {Lars Ahlfors},
     title = {Ueber die {Kreise,} die von einer {Riemannschen} {Fl\"ache} schlicht \"uberdeckt werden.},
     journal = {Commentarii mathematici Helvetici},
     pages = {28--38},
     year = {1933},
     volume = {5},
     zbl = {0006.26301},
     url = {http://geodesic.mathdoc.fr/item/CMH_1933__5_138592/}
}