@article{GDZPPN002237229, title = {Affine umbilical surfaces in R4.}, journal = {Manuscripta mathematica}, volume = {86}, year = {1995}, pages = {275-290}, zbl = {0852.53014}, url = {http://dml.mathdoc.fr/item/GDZPPN002237229} }
Magid, M.; Scharlach, C.; Vrancken, L. Affine umbilical surfaces in R4.. Manuscripta mathematica, Tome 86 (1995) pp. 275-290. http://gdmltest.u-ga.fr/item/GDZPPN002237229/