A characterization of ...-classes of semigroups as partial groupoids. A.H. Clifford, T.E. Hall (1974) Semigroup forum
A characterization of left cancellative monoids by flatness properties. S. Bulman-Fleming, k. McDowell (1990) Semigroup forum
A characterization of semigroups which are semilattices of groups S. Lajos (1970) Colloquium Mathematicae
A characterization of semilattices of left or right groups Bedřich Pondělíček (1972) Czechoslovak Mathematical Journal
A class of semigroups having almost trivial multiplications. M. Mislove, J.F. Berglund (1972) Semigroup forum
A completion theorem for finitely generated commutative semigroups. Pierre Antoine Grillet (1974) Semigroup forum