@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/