1. Ait-Kaci, H.; Nasr, R.: Login, A Logic Programming Language with Built-in Inheritance. J. Logic Programming (1986)3, 185–215
2. Brachman, R.J.; Schmolze, J.G.: An Overview of the KL-ONE Knowledge Representation System. Cognitive Science, Vol. 9, No. 2, April 1985
3. Bürckert, H-J.: Extending the Warren Abstract Machine to Many-Sorted Prolog. Memo Seki-85-VII-KL, Universität Kaiserslautern, Fachbereich Informatik, 1985
4. Clocksin, W.F.; Mellish, C.S.: Programming in Prolog. Second Edition. Springer-Verlag (1984)
5. Cohn, A.G.: Improving the Expressiveness of many-sorted Logic. AAAI-83, Washington (1983)