1. A Course in Universal Algebra;Burris,1981
2. Regularity and permutability of congruences;Chajda;Algebra Universalis,1981
3. Characterization of regular varieties;Csákány;Acta Sci. Math. (Szeged),1970
4. Universal Algebra;Grätzer,1968
5. Ideals in universal algebra;Gumm;Algebra Universalis,1984