Published online by Cambridge University Press: 12 March 2014
A Boolean product construction is used to give examples of existentially closed algebras in the universal Horn class ISP(K) generated by a universal class K of finitely subdirectly irreducible algebras such that Γa(K) has the Fraser-Horn property. If ⟦a ≠ b⟧ ∩ ⟦c ≠ d ⟧ = ∅ is definable in K and K has a model companion of K-simple algebras, then it is shown that ISP(K) has a model companion. Conversely, a sufficient condition is given for ISP(K) to have no model companion.
The results presented in this paper form a part of the author's Ph.D. thesis, completed at the University of Waterloo in 1984 under Professor Stanley Burris, whose supervision and assistance is gratefully acknowledged.