@article{MOMA_1996__122_3_178735,
     author = {J.B. Wilker and V.C. Dumir and R.J. Hans-Gill},
     title = {The {View-Obstruction} {Problem} for {Spheres} in ...5.},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {21--34},
     publisher = {mathdoc},
     volume = {122},
     number = {3},
     year = {1996},
     zbl = {0856.11033},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1996__122_3_178735/}
}