@article{CMH_1938__11_138716,
     author = {H. Hopf and M. Rueff},
     title = {\"Uber faserungstreue {Abbildungen} der {Sph\"aren.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {49--61},
     publisher = {mathdoc},
     volume = {11},
     year = {1938},
     zbl = {0019.37204},
     url = {http://geodesic.mathdoc.fr/item/CMH_1938__11_138716/}
}