1. Pure and Applied Mathematics, Vol. 44;Behrens, Ernst-August,1972
2. The arithmetic of the quasi-uniserial semigroups without zero;Behrens, Ernst-August;Canadian J. Math.,1971
3. Mathematical Surveys, No. 7;Clifford, A. H.,1961
4. On right zero unions of commutative semigroups;Dickinson, Robert P., Jr.;Pacific J. Math.,1972
5. The translational hull of an 𝑁-semigroup;Hall, Robert E.;Pacific J. Math.,1972