@inproceedings{NACLP-1990-LeviMP,
	author        = "Giorgio Levi and Maurizio Martelli and Catuscia Palamidessi",
	booktitle     = "{Proceedings of the North American Conference on Logic Programming, 2 Volumes}",
	isbn          = "0-262-54058-4",
	pages         = "3--22",
	publisher     = "{MIT Press}",
	title         = "{Failure and Success made Symmetric}",
	year          = 1990,
}