@article{1270130496, author = {CHENG, Jih-Hsin}, title = {Curvature Functions for the Sphere in Pseudohermitian Geometry}, journal = {Tokyo J. of Math.}, volume = {14}, number = {2}, year = {1991}, pages = { 151-163}, language = {en}, url = {http://dml.mathdoc.fr/item/1270130496} }
CHENG, Jih-Hsin. Curvature Functions for the Sphere in Pseudohermitian Geometry. Tokyo J. of Math., Tome 14 (1991) no. 2, pp. 151-163. http://gdmltest.u-ga.fr/item/1270130496/