1. Adámek J., Herrlich H., Strecker G.E.: Abstract and Concrete Categories: the Joy of Cats. Wiley-Intersci. Publ., New York (1990)
2. Andréka, H., Sain, I.: Connections between algebraic logic and initial algebra semantics of CF languages. In: Mathematical Logic in Computer Science (Salgotarjan/Hung. 1978). Colloq. Math. Soc. J. Bolyai, vol. 26, pp. 25–83. North-Holland (1981)
3. Bénabou, J.: Structures algèbriques dans les catégories. PhD thesis, Univ. Paris (1966)
4. Bénabou J.: Structures algèbriques dans les catégories. Cahiers Topol. Géom. Différ. 10, 1–126 (1968)
5. Burmeister P.: A Model Theoretic Oriented Approach to Partial Algebras. Akademie-Verlag, Berlin (1986)