@article{GDZPPN002485192, title = {View-Obstruction Problem for 3-dimensional Spheres.}, journal = {Monatshefte f\"ur Mathematik}, volume = {102}, year = {1986}, pages = {279-290}, zbl = {0588.10034}, url = {http://dml.mathdoc.fr/item/GDZPPN002485192} }
Dumir, V.C.; Hans-Gill, R.J. View-Obstruction Problem for 3-dimensional Spheres.. Monatshefte für Mathematik, Tome 102 (1986) pp. 279-290. http://gdmltest.u-ga.fr/item/GDZPPN002485192/