@inproceedings{PODS-1986-GuchtF,
	author        = "Dirk Van Gucht and Patrick C. Fischer",
	booktitle     = "{Proceedings of the Fifth Symposium on Principles of Database Systems}",
	doi           = "10.1145/6012.15405",
	isbn          = "0-89791-179-2",
	pages         = "60--69",
	publisher     = "{ACM}",
	title         = "{Some Classes of Multilevel Relational Structures}",
	year          = 1986,
}