@article{GDZPPN002428253, title = {On Embedded 2-Spheres in 3-Manifolds.}, journal = {Mathematische Zeitschrift}, volume = {183}, year = {1983}, pages = {235-244}, zbl = {0507.57008}, url = {http://dml.mathdoc.fr/item/GDZPPN002428253} }
Wicha-Krause, Bärbel. On Embedded 2-Spheres in 3-Manifolds.. Mathematische Zeitschrift, Tome 183 (1983) pp. 235-244. http://gdmltest.u-ga.fr/item/GDZPPN002428253/