1) A.H. Clifford, G.B. Preston, The Algebraic Theory of SemigroupsVol 1, American Mathematical Society 1961

2) John M. Howie, Fundamentals of Semigroup Theory, Clarendon Press Oxford1995

3) Otto Steinfeld, Quasi-Ideals in Rings and Semigroups, Akademia Kiado, Budapest 1978

4) F.M. Sioson, Ideal Theory in Ternary Semigroups, Math.Jpn. 10, 63-84 1965

5) D.H. Lehmer, A Ternary Analogue of Abelian Groups, Am.J.Math. 54, 329-338 1932

6) J.Los, On the Extending of Models I.Fundam.Math.42, 38-54 1955 

7) J.von Neumann, On Regular Rings, Proc. Nat. Acad. Sci. USA 22, 707-713 1936

Department of Mathematical Engineering, Polytechnic University of Tirana, Tirana, Albania anila87@outlook.com