@inproceedings{OOPSLA-ECOOP-1990-LeavensW,
	author        = "Gary T. Leavens and William E. Weihl",
	booktitle     = "{Proceedings of the Fifth Conference on Object-Oriented Programming, Systems, Languages and Applications / Fourth European Conference on Object-Oriented Programming}",
	doi           = "10.1145/97945.97970",
	editor        = "Akinori Yonezawa",
	isbn          = "0-89791-411-2",
	pages         = "212--223",
	publisher     = "{ACM}",
	title         = "{Reasoning about Object-Oriented Programs that Use Subtypes}",
	year          = 1990,
}