@article{oai:tsukuba.repo.nii.ac.jp:00015849, author = {Gao, Zhi Min and Hattori, Yasunao}, issue = {2}, journal = {Tsukuba Journal of Mathematics}, month = {Dec}, pages = {367--370}, title = {A characterization of closed s-images of metric spaces}, volume = {11}, year = {1987} }