@phdthesis{oai:tsukuba.repo.nii.ac.jp:00020900,
 author = {安井, 義和 and Yasui, Yoshikazu},
 month = {},
 note = {1991},
 school = {筑波大学, University of Tsukuba},
 title = {Shrinking properties of open covers},
 year = {1992}
}