@article{oai:tsukuba.repo.nii.ac.jp:00015926,
author = {Sato, Kojiro},
issue = {2},
journal = {Tsukuba journal of mathematics},
month = {Dec},
note = {Let S be a torsion-free cancellative commutative (additive) semigroup ⊇{0}. Let G be the quotient group if S. We assume G≠S. For each subset A of G, we set A-1={x∈G: x+A⊂S} and (A-1)-1=A. ...},
pages = {497--503},
title = {Notes on M-semigroups},
volume = {14},
year = {1990}
}