@article{MAN_1924__91_159045,
     author = {J. Nielsen},
     title = {Die {Isomorphismengruppe} der freien {Gruppen}},
     journal = {Mathematische Annalen},
     pages = {169--209},
     publisher = {mathdoc},
     volume = {91},
     year = {1924},
     zbl = {50.0078.04},
     url = {http://geodesic.mathdoc.fr/item/MAN_1924__91_159045/}
}