@article{oai:tsukuba.repo.nii.ac.jp:00017137,
 author = {Yu, Zuhuan},
 issue = {3},
 journal = {Tsukuba Journal of Mathematics},
 month = {Dec},
 pages = {575--588},
 title = {The inverse surface and the Osserman inequality},
 volume = {22},
 year = {1998}
}