@inproceedings{PPDP-2001-RychlikowskiT,
	author        = "Pawel Rychlikowski and Tomasz Truderung",
	booktitle     = "{Proceedings of the Third International Conference on Principles and Practice of Declarative Programming}",
	isbn          = "1-58113-388-X",
	pages         = "61--72",
	publisher     = "{ACM}",
	title         = "{Polymorphic Directional Types for Logic Programming}",
	year          = 2001,
}