1. H. Andréka, P. Burmeister andI. Németi, Quasivarieties of partial algebras—A unifying approach towards a two-valued model theory for partial algebras,Studia Sci. Math. Hungar. 16 (1983), 325–372.MR 85i: 08003
2. H. Andréka andI. Németi, Injectivity in categories to represent all first order formulas, I,Demonstratio Math. 12 (1979), 717–732.MR 81h: 03082
3. H. Andréka andI. Németi, Generalization of the concept of variety and quasivariety to partial algebras through category theory,Dissertationes Math. (Rozprawy Mat.) No. 204, 1983.MR 85c: 08006
4. Colloq. Mat. Soc. J. Bolyai;H. Andréka,1981
5. R. M. Burstall andJ. A. Goguen, Putting theories together to make specifications,Proc. Fifth Intern. Joint Conf. on Artificial Intelligence, Cambridge (Mass.), 1977.