@article{GDZPPN00248904X,
title = {A Markoff-Type Chain for the View-Obstruction Problem for Spheres in R4.},
journal = {Monatshefte f\"ur Mathematik},
volume = {118},
year = {1994},
pages = {205-218},
zbl = {0818.52013},
url = {http://dml.mathdoc.fr/item/GDZPPN00248904X}
}
Dumir, V.C.; Hans-Gills, R.J. A Markoff-Type Chain for the View-Obstruction Problem for Spheres in R4.. Monatshefte für Mathematik, Tome 118 (1994) pp. 205-218. http://gdmltest.u-ga.fr/item/GDZPPN00248904X/