1. [ABN 80] H. Andréka, P. Burmeister and I. Németi.Quasivarieties of partial algebras—A unifying approach towards a two-valued model theory for partial algebras. Preprint Nr. 557, TH Darmstadt, 1980; also in: Studia Sci. Math. Hungar. to appear.
2. [AN 76] H. Andréka and I. Németi.Generalization of variety and quasivariety concept to partial algebras through category theory. Math. Inst. Hung. Acad. Sci. Preprint No. 5/1976. (To appear in Dissertationes Mathematicae (Rozprawy Mat.) No. 204.)
3. Colloq. Math. Soc. J. Bolyai;H. Andréka,1981
4. [AN 78] H. Andréka and I. Németi.Łos' lemma holds in every category. Studia Scientiarum Math. Hung.13, 1978, pp. 361–376.
5. [AN 79] H. Andréka and I. Németi.Formulas and ultraproducts in categories. Beiträge zur Algebra und Geometrie,8, 1979, pp. 133–151.