1. Howie, J.M.: Fundamentals of Semigroup Theory. Clarendon, Oxford (1995)
2. Mikhalev, A.V., Pilz, G.F. (eds.): The Concise Handbook of Algebra. Kluwer Academic, Dordrecht (2002)
3. Pastijn, F., Volkov, M.V.: Minimal noncryptic e-varieties of regular semigroups. J. Algebra 184, 881–896 (1996)
4. Petrich, M., Reilly, N.R.: Completely Regular Semigroups. Wiley, New York (1999)
5. Rotman, J.J.: Advanced Modern Algebra. Pearson Education, Upper Saddle River (2002)