@article{MZ_1977__157_172608,
     author = {Ulrich Hirsch},
     title = {On {Branched} {Coverings} of the {3-Sphere.}},
     journal = {Mathematische Zeitschrift},
     pages = {225--236},
     publisher = {mathdoc},
     volume = {157},
     year = {1977},
     zbl = {0347.57002},
     url = {http://geodesic.mathdoc.fr/item/MZ_1977__157_172608/}
}