1. Addition von Korrespondenzen in abelschen Kategorien;Brinkmann;Math Z.,1970
2. Abelsche und exakte Kategorien, Korrespondenzen;Brinkmann,1969
3. On properties of rings that can be characterized by infinite lattice identities;Czédli;Studia Sci. Math. Hungar.,1981
4. Computability and Unsolvability;Davis,1958
5. Universal Algebra;Grätzer,1979