1. Bergman, C.: Universal Algebra. Fundamentals and Selected Topics, Pure and Applied Mathematics (Boca Raton), vol. 301. CRC Press, Boca Raton, FL (2012)
2. Bergman C., Berman J.: Fully invariant and verbal congruence relations. Algebra Universalis 70, 71–94 (2013)
3. Clark, D.M., Davey, B.A.: Natural Dualities for the Working Algebraist, Cambridge Studies in Advanced Mathematics, vol. 57. Cambridge University Press, Cambridge (1998)
4. Werner, H.: Discriminator Algebras. Studium zur Algebra und ihre Andwendungen 6. Akademie Verlag, Berlin (1978)