[1] CLIFFORD A. H., PRESTON G. B.: The Algebraic Theory of Semigroups. Vol. I; Vol. II, Amer. Math. Soc., Providence, R.I., 1961; 1967. MR 0132791 | Zbl 0111.03403

[2] CLIFFORD A. H.: Semigroups admitting relative inverses. Ann. of Math. 42 (1941). 1037-1049. MR 0005744 | Zbl 0063.00920

[3] CLIFFORD A. H.: Semigroups containing minimal ideals. Amer. J. Math. 70 (1948). 521-526. MR 0025476 | Zbl 0038.01103

[4] CLIFFORD A. H.: Semigroups without nilpotent ideals. Amer. J. Math.71 (1949). 834-844. MR 0032661 | Zbl 0045.30101

[5] IVAN J.: On a decomposition of simple semigroups to direct product. (Slovak). Mat. Čas. 4 (1954), 181-201. MR 0072881

[6] LYAPIN E. S.: Semigroups. (Russian), Nauka, Moskva, 1960. Zbl 0128.02703

[7] REES D.: Note on semigroups. Math. Proc. Cambridge Philos. Soc. 37 (1941). 334- 435. MR 0005743

[8] SCHWARZ S.: Theory of semigroups. (Slovak), Sborník Prírodov. Fak. Slov. Univ. no. 6 (1943), 1-64. MR 0407170

[9] SCHWARZ S.: A structure of simple semigroups without zero. (Russian). Czechoslovak Math. J. 1(76) (1951), 51-65. MR 0048428

[10] SCHWARZ S.: On semigroups having a kernel. (Russian), Czechoslovak Math. J. 1(76) (1951), 259-301. MR 0051221

[11] SUSCHEWITSCH A.: Über die endlichen Gruppen ohne Gesetz der eindestigen Umkehrbarkeit. Math. Ann. 99 (1982), 30-50.

[12] ABRHAN I.: On J-subalgebras in unary algebras on simple ideals and J-ideals in groupoids and semigroups. (Russian), Math. Slovaca 28 (1978), 61-80. MR 0527775

[13] ABRHAN I.: On minimal ideals of semigroups with respect to their subsets. I. Math. Bohemica (Submitted).