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@article{MAN_1974__210_162616, author = {Katsumi Nomizu and Kentaro Yano}, title = {On {Circles} and {Spheres} in {Riemannian} {Geometry.}}, journal = {Mathematische Annalen}, pages = {163--170}, publisher = {mathdoc}, volume = {210}, year = {1974}, zbl = {0273.53039}, url = {http://geodesic.mathdoc.fr/item/MAN_1974__210_162616/} }
Katsumi Nomizu; Kentaro Yano. On Circles and Spheres in Riemannian Geometry.. Mathematische Annalen, Tome 210 (1974), pp. 163-170. http://geodesic.mathdoc.fr/item/MAN_1974__210_162616/