@inproceedings{POPL-1973-Morris,
	author        = "James H. Morris Jr.",
	booktitle     = "{Conference Record of the First Symposium on Principles of Programming Languages}",
	doi           = "10.1145/512927.512938",
	editor        = "Patrick C. Fischer and Jeffrey D. Ullman",
	pages         = "120--124",
	publisher     = "{ACM Press}",
	title         = "{Types are Not Sets}",
	year          = 1973,
}