@article{CMH_1942__15_138799,
     author = {Heinz Hopf},
     title = {Maximale {Toroide} und singul\"are {Elemente} in geschlossenen {Lieschen} {Gruppen.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {59--70},
     publisher = {mathdoc},
     volume = {15},
     year = {1942},
     zbl = {0027.09601},
     url = {http://geodesic.mathdoc.fr/item/CMH_1942__15_138799/}
}