1. R.M. Amadio and L. Cardelli. Subtyping recursive types. In 18th POPL, Orlando (FL, US), 1991.
2. R.J. Brachman, D.L. McGuinness, P.F. Patel-Schneider, L.A. Resnick, and A. Borgida. Living with CLASSIC, When and how to use a KL-ONE-like language, chapter 14, pages 401–456. Principles of semantic networks. Morgan Kaufmann, 1991.
3. A. Borgida. From type systems to knowledge representation: natural semantic specifications for description logics. International Journal of Intelligent and Cooperative Information Systems, 1(1):93–126, April 1992.
4. Cognitive Science;RJ Brachman,1985
5. C. Capponi. Classification des classes par les types. In EC2, editor, Représentations Par Objets, pages 215–224, La Grande Motte, France, June 1993.