View-Obstruction Problem for 3-dimensional Spheres. V.C. Dumir; R.J. Hans-Gill — 1986 Monatshefte für Mathematik
A Markoff-Type Chain for the View-Obstruction Problem for Spheres in R4. V.C. Dumir; R.J. Hans-Gills — 1994 Monatshefte für Mathematik
The View-Obstruction Problem for Spheres in ...5. J.B. Wilker; V.C. Dumir; R.J. Hans-Gill — 1996 Monatshefte für Mathematik