1. Adámek, J., Herrlich, H., Strecker, G.E.: Abstract and concrete categories. Wiley Interscience, Hoboken (1990)
2. Lecture Notes in Computer Science,2004
3. Broy, M., Facchi, C., Grosu, R., Hettler, R., Hussmann, H., Nazareth, D., Regensburger, F., Stølen, K.: The requirement and design specification language SPECTRUM, Tech. report, Technical University of Munich (1993)
4. Bucalo, A., Führmann, C., Simpson, A.: Equational lifting monads. In: Category Theory and Computer Science. ENTCS, vol. 29 (1999)
5. Burmeister, P.: A model theoretic oriented approach to partial algebras. Akademie- Verlag (1986)