1. Fraser, G. A., andA. Horn: Congruence relations in direct products. Proc. A. M. S.26, 390–394 (1970).
2. Grätzer, G.: Notes on lattice theory II: On Boolean functions. Rev. Roumaine Math. Pures Appl.7, 693–697 (1962).
3. Grätzer, G.: Universal Algebra. Toronto-London-Melbourne: Van Nostrand. 1968.
4. Iskander, A.: Algebraic functions onp-rings. Coll. Math.25, 37–41 (1972).
5. Lausch, H., andW. Nöbauer: Algebra of Polynomials. Amsterdam-London-New York: North-Holland. 1973.