@inproceedings{PODS-1994-LibkinW,
	author        = "Leonid Libkin and Limsoon Wong",
	booktitle     = "{Proceedings of the 13th Symposium on Principles of Database Systems}",
	doi           = "10.1145/182591.182609",
	isbn          = "0-89791-642-5",
	pages         = "155--166",
	publisher     = "{ACM Press}",
	title         = "{New Techniques for Studying Set Languages, Bag Languages and Aggregate Functions}",
	year          = 1994,
}