1. Birkhoff, G.,On the structure of abstract algebras. Proceedings of the Cambridge Phil. Soc.31 (1935), 434–454.
2. Dudek, J. andGraczyńska, E.,The lattice of varieties of algebras. Bull. Pol. Acad. Sci.29 (7, 8) (1981), 337–340.
3. Grätzer, G.,Universal Algebra. Springer-Verlag, Berlin, 1979.
4. Graczyńska, E.,On bases for normal identities. Studia Sci. Math. Hungarica19 (1984), 317–320.
5. Graczyńska, E.,On regular identities. Algebra Universalis17 (1983), 369–375.