@inproceedings{VLDB-1978-SagivY,
	author        = "Yehoshua Sagiv and Mihalis Yannakakis",
	booktitle     = "{Proceedings of the Fourth International Conference on Very Large Data Bases}",
	cdrom         = "VLDB78/P535.PDF",
	pages         = "535--548",
	publisher     = "{IEEE Computer Society}",
	title         = "{Equivalence among Relational Expressions with the Union and Difference Operation}",
	year          = 1978,
}