1. Fundamental notions in the theory of seminearrings;Van Hoorn;Compositio Mathematica,1967
2. Near-Rings;Pilz,1983
3. A note on middle unitary semigroups;Yamada;Kodai Mathematical Seminar Reports,1955
4. Semigroups with midunits;Ault;Transactions of the American Mathematical Society,1974
5. On middle units in orthodox semigroups;Blyth;Semigroup Forum,1976