@article{oai:tsukuba.repo.nii.ac.jp:00016069,
 author = {Enochs, Edgar E. and Jenda, Overtoun M.G. and Xu, Jinzhong},
 issue = {2},
 journal = {Tsukuba Journal of Mathematics},
 month = {Dec},
 pages = {487--503},
 title = {Covers and envelopes over Gorenstein rings},
 volume = {20},
 year = {1996}
}