@article{CMH_1931__3_138559,
     author = {Lars Ahlfors},
     title = {Zur {Bestimmung} des {Typus} einer {Riemannschen} {Fl\"ache.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {173--178},
     publisher = {mathdoc},
     volume = {3},
     year = {1931},
     zbl = {57.0370.03},
     url = {http://geodesic.mathdoc.fr/item/CMH_1931__3_138559/}
}