@article{CMH_1943__16_138827,
     author = {Heinz Hopf},
     title = {Enden offener {R\"aume} und unendliche diskontinuierliche {Gruppen.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {81--100},
     publisher = {mathdoc},
     volume = {16},
     year = {1943},
     zbl = {0060.40008},
     url = {http://geodesic.mathdoc.fr/item/CMH_1943__16_138827/}
}