@article{MAN_1931__105_159502,
     author = {W. Magnus},
     title = {Untersuchungen \"uber einige unendliche diskontinuierliche {Gruppen}},
     journal = {Mathematische Annalen},
     pages = {52--74},
     publisher = {mathdoc},
     volume = {105},
     year = {1931},
     zbl = {57.0151.01},
     url = {http://geodesic.mathdoc.fr/item/MAN_1931__105_159502/}
}