@inproceedings{PLILP-1990-Nilsson,
	author        = "Ulf Nilsson",
	booktitle     = "{Proceedings of the Second International Workshop on Programming Language Implementation and Logic Programming}",
	doi           = "10.1007/BFb0024191",
	isbn          = "3-540-53010-X",
	pages         = "293--306",
	publisher     = "{Springer-Verlag}",
	series        = "{Lecture Notes in Computer Science}",
	title         = "{Systematic Semantic Approximations of Logic Programs}",
	volume        = 456,
	year          = 1990,
}