@inproceedings{ICLP-1991-KoN,
	author        = "Hai-Ping Ko and Mark E. Nadel",
	booktitle     = "{Proceedings of the Eighth International Conference on Logic Programming}",
	isbn          = "0-262-56058-5",
	pages         = "679--692",
	publisher     = "{MIT Press}",
	title         = "{Substitution and Refutation Revisited}",
	year          = 1991,
}