[1] Clifford A. H., Preston G. В.: The Algebraic theory of semigroups. Math. Surveys of the American Math. Soc. 7 Vol. 1 (Providence, R.I., 1961). MR 0132791 | Zbl 0111.03403

[2] Kapp K. M.: On Bi-ideals and Quasi-ideals in Semigroups. Publ. Math. Debrecen, 16 (1969), 179-185. MR 0267018

[3] Krgovic D. N.: On (m, n)-regular Semigroups. Publ. Inst. Math. Belgrade 18 (32) (1975), 107-110. MR 0369578 | Zbl 0307.20041

[4] Lajos Sandor: Generalized Ideals in Semigroups. Acta Sci. Math., 22 (1961), 217-222. MR 0136671