@book{1993-vandeusen ,title={{Proceedings of the 20th ACM SIGPLAN-SIGACT symposium on principles of programming languages}} ,booktitle={{Proceedings of the 20th ACM SIGPLAN-SIGACT symposium on principles of programming languages}} ,author={Mary Van Deusen (chairman) and Bernard Lang (chairman)} ,ISBN={0--89791--560--7} ,publisher={Association for Comuting Machinery} ,address={New York} ,year={1993} }