Y. Yokote. Proceedings of the 7th ACM Conference on Object-Oriented Programming
Systems, Languages, and Applications (OOPSLA-92), volume 27, 10 of ACM SIG\-PLAN Notices, page 414--434. ACM Press, (1992)
D. Yellin, and R. Strom. Proceedings of the 9th ACM Conference on Object-Oriented Programming
Systems, Languages and Applications (OOPSLA-94), volume 29, 10 of ACM Sigplan Notices, page 176--190. (1994)