@article{oai:tsukuba.repo.nii.ac.jp:00017125,
 author = {Kozaki, Masanori and Maeda, Sadahiro},
 issue = {2},
 journal = {Tsukuba Journal of Mathematics},
 month = {Dec},
 pages = {291--297},
 title = {A characterization of extrinsic spheres in a Riemannian manifold},
 volume = {26},
 year = {2002}
}