1. Non-well-founded sets;Aczel,1988
2. Metalanguage and reasoning across viewpoints;Attardi,1984
3. G. Attardi and M. Simi (1991). Reflections about reflection, in Allen, J. A., Fikes, R., and Sandewall, E. (eds.) Principles of Knowledge Representation and Reasoning: Proceedings of the Second International Conference. Morgan Kaufmann, San Mateo, California.
4. A formalisation of viewpoints;Attardi,1993
5. Amalgamating language and metalanguage in logic programming;Bowen,1982