1. Burris, S., Werner, H.: Sheaf constructions and their elementary properties. II. Darmstadt 1975 (preprint).
2. Cherlin, G.: Lindenbaum algebras and model companions. Rutgers University 1976 (preprint).
3. Eklof, P., Sabbagh, G.: Model completions and modules. Ann. math. logic2, 251–295 (1971).
4. Engeler, E.: A characterization of theories with isomorphic denumerable models. Notices AMS6, 161 (1959).
5. Grätzer, G.: Lattice theory. San Francisco: Freeman 1971.