@article{oai:tsukuba.repo.nii.ac.jp:00015926,
 author = {Sato, Kojiro},
 issue = {2},
 journal = {Tsukuba Journal of Mathematics},
 month = {Dec},
 pages = {497--503},
 title = {Notes on M-semigroups},
 volume = {14},
 year = {1990}
}