1. Dénes, J.: On Transformations, Transformation semigroups and Graphs, Theory of Graphs. Proc. Colloq. Tihany, 65–75 (1966)
2. Bayramov, P. A.: On the problem of completeness in a symmetric semigroup of finite degree (in Russian). Diskret Analiz, 8, 3–27 (1966). MR 34, 7682
3. Liebeck, M. W., Praeger, C. E., Saxl, J.: A classification of the maximal subgroups of the finite alternating and symmetric groups. J. Algebra, 111, 365–383 (1987)
4. Todorov, K., Kracolova, L.: On the maximal subsemigroups of the ideals of finite symmetric semigroups. Simon Stevin, 59(2), 129–140 (1985)
5. Yang, X. L.: Maximal subsemigroups of finite singular transformation semigroups. Communications in Algebra, 29(3), 1175–1182 (2001)