1. Bosak, J.: The graphs of semigroups. In: Theory of Graphs and Application, pp. 119–125. Academic Press, New York (1964)
2. Budden, F.: Cayley graphs for some well-known groups. Math. Gaz. 69, 271–278 (1985)
3. Gallian, J.A.: Contemporary Abstract Algebra. Narosa Publishing House, London (1999)
4. Howie, J.M.: An Introduction to Semigroup Theory. Academic Press, London (1976)
5. Hungerford, T.W.: Algebra. Springer, Berlin (1974)