@article{CMH_1986__61_140047,
     author = {Wolfgang Ziller and Hermann Gluck},
     title = {On the volume of a unit vector field on the three-sphere.},
     journal = {Commentarii mathematici Helvetici},
     pages = {177--192},
     publisher = {mathdoc},
     volume = {61},
     year = {1986},
     zbl = {0605.53022},
     url = {http://geodesic.mathdoc.fr/item/CMH_1986__61_140047/}
}