Jon G. Riecke, Ramesh Subrahmanyam. Extensions to Type Systems Can Preserve Operational Equivalences. In Masami Hagiya, John C. Mitchell, editors, Theoretical Aspects of Computer Software, International Conference TACS 94, Sendai, Japan, April 19-22, 1994, Proceedings. Volume 789 of Lecture Notes in Computer Science, pages 76-95, Springer, 1994.