1. Roberto M. Amadio and Luca Cardelli. Subtyping recursive types. ACM Transactions on Programming Languages and Systems, 15(4):575–631, September 1993.
2. Marcin Benke. Efficient type reconstruction in the presence of inheritance. Technical Report TR 94-10(199), Institute of Informatics, Warsaw University, December 1994.
3. Marcin Benke. Some complexity bounds for subtype inequalities. Technical Report TR 95-20(220), Institute of Informatics, Warsaw University, 1995.
4. François Bourdoncle and Stephan Merz. Type checking higher-order polymorphic multi-methods. In Conference Record of the 24th Annual ACM Symposium on Principles of Programming Languages, pages 302–315, Paris, January 1997. ACM.
5. Franz Baader and Jörg H. Siekmann. Unification theory. In D.M. Gabbay, C.J. Hogger, and J.A. Robinson, editors, Handbook of Logic in Artificial Intelligence and Logic Programming. Oxford University Press, Oxford, UK, 1994.