1. Roberto M. Amadio and Luca Cardelli. Subtyping recursive types. In Conference Record of the Eighteenth Annual ACM Symposium on Principles of Programming Languages (POPL'91), pages 104–118, ACM Press, 1991. Extended abstract. Full version in [AC92].
2. Roberto M. Amadio and Luca Cardelli. Subtyping Recursive Types. Technical Report 133, INRIA, Institut National de Recherche en Informatique et en Automatique, Lorraine, February 1992.
3. Alexander Aiken and Brian M. Murphy. Implementing regular tree expressions. In J. Hughes, editor, Proceedings of the 5th A CM Conference on Functional Programming Languages and Computer Architecture (FPCA '91), Cambridge, MA, USA, August 1991, volume 523 of Lecture Notes in Computer Science, pages 427–447, Springer-Verlag, 1991.
4. Alexander Aiken and Brian M. Murphy. Static type inference in a dynamically typed language. In Conference Record of the Eighteenth Annual ACM Symposium on Principles of Programming Languages (POPL '91), pages 279–290, ACM Press, 1991.
5. Alexander Aiken and Edward L. Wimmers. Solving systems of set constraints (extended abstract). In Proceedings of the Seventh Annual IEEE Symposium on Logic in Computer Science (LICS'92), Santa Cruz, California, June 1992, pages 329–340, IEEE Computer Society, IEEE Computer Society Press, 1992.