1. Bonnier, S. and J. Małuszyński. Towards a clean amalgamation of logic programs with external procedures. In 5th Int. conf. and symp. on logic programming, pp. 311–326, MIT Press, 1988.
2. Bonnier, S. Horn clause logic with external procedures: towards a theoretical framework, Licenciate thesis, University of Linköping, Sweden, 1989.
3. Research report;S. Bonnier,1990
4. Bruynooghe M. A framework for the abstract interpretation of logic programs. Report CW62, Katholieke Universiteit, Leuven, 1987.
5. Research report;P. Deransart,1989