1. Aquilano, C. and Bocchetti, P., ‘Caratterizzazione di una teoria in clausole Horn per una deduzione completa di informazioni negative’, Master's Thesis, Dept. of Comp. Science, University of Pisa, (1985).
2. Asirelli, P., Barbuti, R., and Levi, G., ‘Types and declarative static type checking in logic programming’, Proc. Programming '84, Primorsko, Bulgary (1984).
3. Barbuti, R. and Martelli, M., ‘Programming in a generally functional style to design logic databases’, CASE Center Technical Report No. 8602, Syracuse University (1986).
4. ClarkK. L., Negation as Failure, inLogic and Data Bases (eds. H.Gallaire, and J.Minker), Plenum, New York, pp. 293–322 (1978).
5. Jaffar, J., Lassez, J.-L., and Lloyd, J. W., ‘Completeness of the Negation-as-Failure Rule’,Proc. 8th IJCAI, Karlsruhe (1983), pp. 500–506.