@inproceedings{SLP-1987-SannellaW87,
	author        = "Donald Sannella and Lincoln A. Wallen",
	booktitle     = "{Proceedings of the Fourth Symposium on Logic Programming}",
	isbn          = "0-8186-0799-8",
	pages         = "368--378",
	publisher     = "{IEEE-CS}",
	title         = "{A Calculus for the Construction of Modular Prolog Programs}",
	year          = 1987,
}