@inproceedings{KR-1991-Kaufman,
	author        = "Stephen G. Kaufman",
	booktitle     = "{Proceedings of the Second International Conference on Principles of Knowledge Representation and Reasoning}",
	isbn          = "1-55860-165-1",
	pages         = "347--356",
	publisher     = "{Morgan Kaufmann}",
	title         = "{A Formal Theory of Spatial Reasoning}",
	year          = 1991,
}