@article{GDZPPN002023482, title = {Nearly Spherical Surfaces.}, journal = {Aequationes mathematicae}, volume = {2}, year = {1969}, pages = {186-193}, zbl = {0177.49501}, url = {http://dml.mathdoc.fr/item/GDZPPN002023482} }
Guggenheimer, H. Nearly Spherical Surfaces.. Aequationes mathematicae, Tome 2 (1969) pp. 186-193. http://gdmltest.u-ga.fr/item/GDZPPN002023482/