1. Birjukov, A. P., Varieties of idempotent semigroups, Algebra and Logic 9:153–164, 1970. translation of Algebra i Logika 9:255–273, 1970.
2. Bol’bot, A. D., Finite basing of identities of four-element semigroups, Siberian Mathematical Journal 20(2): 323, 1979. translation of Sibirsk. Mat. Zh. 20(2):451, 1979.
3. Burris, S., and H. P. Sankappanavar, A Course in Universal Algebra, Springer-Verlag, 1981.
4. Distler A., Kelsey T.: The monoids of orders eight, nine & ten. Annals of Mathematics and Artificial Intelligence 56, 3–25 (2009)
5. Distler, A., and J. D. Mitchell, Smallsemi – a GAP package, version 0.6.2, 2010., available at http://www.gap-system.org/Packages/smallsemi.html .