[1] Clifford A. H., G. B. Preston: The algebraic theory of semigroups, vol. I. Amer. Math. Soc., Providence, 1961. MR 0132791 | Zbl 0111.03403

[2] Fabrici I.: On complete ideals in semigroups. Mat. Časopis Sloven. Akad. Vied 18 (1968), 34-39. MR 0238978 | Zbl 0169.02902

[3] Lajos S.: Generalized ideals in semigroups. Acta Sci. Math., 22 (1961), 217-222. MR 0136671 | Zbl 0108.25904

[4] Lajos S.: On the characterization of completely regular semigroups. Math. Japonicae (Special Issue) 20 (1975), 33-35. MR 0396806

[5] Lajos S.: Some characterizations of completely regular semigroups. Kyungpook Math. J. i9(1979),213-214. MR 0560453

[6] Miccoli M. M., B. Pondělíček: On $\alpha$-ideals and generalized $\alpha$-ideals in semigroups. (to appear). MR 1006318

[7] Steinfeld O.: Quasi-ideals in rings and semigroups. Akadémiai Kiadó, Budapest, 1978. MR 0521258 | Zbl 0403.16001