@article{GDZPPN002026945, title = {View-Obstruction Problems}, journal = {Aequationes mathematicae}, volume = {9}, year = {1973}, pages = {165-170}, zbl = {0265.52003}, url = {http://dml.mathdoc.fr/item/GDZPPN002026945} }
CUSICK, T.W. View-Obstruction Problems. Aequationes mathematicae, Tome 9 (1973) pp. 165-170. http://gdmltest.u-ga.fr/item/GDZPPN002026945/