1. P. Atzeni, F. Cacace, S. Ceri, L. Tanca. The LOGIDATA+ model. Technical report Logidata+ 5/20, July 1990.
2. K. A. Bowen and R. A. Kowalski. Amalgamating language and metalanguage in logic programming. In K. L. Klark and S. A. Tarnlund Eds., Logic Programming, Academic Press 1982, pages. 153–172
3. K. A. Bowen and T. Weinberg. Ameta-level extention of Prolog. In 1985 IEEE Symposium on Logic Programming, IEEE Computer Socierty Press 1985, pages 48–53
4. A. Brogi, P. Mancarella, D. Pedreschi, F. Turini. A Hierarchies through Basic Meta-Level Operators. In Proc. Workshop on Metaprogramming in Logic, META 90, Leuven, Belgio, May 1990.
5. S. Ceri, G. Gottlob, L. Tanca. Logic Programming and Databases. Springer-Verlag, 1990.