1. Almeida, J.: Finite Semigroups and Universal Algebra, p. xviii+511. World Scientific Publishing Co., Inc., River Edge (1994)
2. Bratchikov, S.N.: Collective identities of semigroups, (Russian) PHD Thesis, St. Petersburg, (1999)
3. Grátzer, G.: Universal Algebra, Universal algebra. With appendices by Grátzer, Bjarni Jónsson, Walter Taylor, Robert W. Quackenbush, Gúnter H. Wenzel, and Grátzer and W. A. Lampe. Revised reprint of the 1979 second edition, pp xx+586. Springer, New York, (2008)
4. Lipyanski, R., Vanetik, N.: Classification problem for graphs and lattices is wild. Translated from Sovrem. Mat. Prilozh. Vol. 79, 2012, Part 2. J. Math. Sci. (N.Y.) 191 (2013), 776–780
5. Lyapin, E.S.: Semigroups, Translated from the 1960 Russian original by A. A. Brown, J. M. Danskin, D. Foley, S. H. Gould, E. Hewitt, S. A. Walker and J. A. Zilber. Third edition. Translations of Mathematical Monographs, Vol. 3, pp xiii+519 . American Mathematical Society, Providence, R.I., (1974)