@article{GDZPPN002309920, title = {On Circles and Spheres in Riemannian Geometry.}, journal = {Mathematische Annalen}, volume = {212}, year = {1974}, pages = {163-170}, zbl = {0273.53039}, url = {http://dml.mathdoc.fr/item/GDZPPN002309920} }
Nomizu, Katsumi; Yano, Kentaro. On Circles and Spheres in Riemannian Geometry.. Mathematische Annalen, Tome 212 (1974) pp. 163-170. http://gdmltest.u-ga.fr/item/GDZPPN002309920/