1. S. Burris andH. P. Sankappanavar,A Course in Universal Algebra. Graduate Texts in Mathematics,78, Springer-Verlag, New York, 1981.
2. S.Burris and R.Willard,Finitely many primitive positive clones. (To appear in the Proc. Amer. Math. Soc.)
3. H. J. Riedel,Existentially closed algebras and the Boolean Product Construction. Univ. of Waterloo, Waterloo, Ontario, 1984. (Ph.D. Thesis).