@article{GDZPPN002301725, title = {On the Distortion of Conformal Immersions between 2-Space Forms.}, journal = {Mathematische Annalen}, volume = {180}, year = {1969}, pages = {159-168}, zbl = {0172.46501}, url = {http://dml.mathdoc.fr/item/GDZPPN002301725} }
HELFENSTEIN, H.G. On the Distortion of Conformal Immersions between 2-Space Forms.. Mathematische Annalen, Tome 180 (1969) pp. 159-168. http://gdmltest.u-ga.fr/item/GDZPPN002301725/