@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/