@article{GDZPPN002489775,
title = {The View-Obstruction Problem for Spheres in ...5.},
journal = {Monatshefte f\"ur Mathematik},
volume = {121},
year = {1996},
pages = {21-34},
zbl = {0856.11033},
url = {http://dml.mathdoc.fr/item/GDZPPN002489775}
}
Wilker, J.B.; Dumir, V.C.; Hans-Gill, R.J. The View-Obstruction Problem for Spheres in ...5.. Monatshefte für Mathematik, Tome 121 (1996) pp. 21-34. http://gdmltest.u-ga.fr/item/GDZPPN002489775/