@article{MZ_1974__140_172143,
     author = {Ulrich Hirsch},
     title = {\"Uber offene {Abbildungen} auf die {3-Sph\"are.}},
     journal = {Mathematische Zeitschrift},
     pages = {203--230},
     publisher = {mathdoc},
     volume = {140},
     year = {1974},
     zbl = {0279.57004},
     url = {http://geodesic.mathdoc.fr/item/MZ_1974__140_172143/}
}