@article{1178241371,
author = {Nomizu, Katsumi},
title = {Generalized central spheres and the notion of spheres in Riemannian geometry},
journal = {Tohoku Math. J. (2)},
volume = {25},
number = {4},
year = {1973},
pages = { 129-137},
language = {en},
url = {http://dml.mathdoc.fr/item/1178241371}
}
Nomizu, Katsumi. Generalized central spheres and the notion of spheres in Riemannian geometry. Tohoku Math. J. (2), Tome 25 (1973) no. 4, pp. 129-137. http://gdmltest.u-ga.fr/item/1178241371/