@incollection{Bennett94spatial,
  author = {Brandon Bennett},
  title = {Spatial Reasoning with Propositional Logics},
  booktitle = {KR'94: Principles of Knowledge Representation and Reasoning},
  publisher = {Morgan Kaufmann},
  year = {1994},
  pages = {51--62},
  url = {citeseer.ist.psu.edu/bennett94spatial.html}
}

@inproceedings{gruber94-ontology_engineering_mathematics,
  author = {Thomas R. Gruber and Gregory R. Olsen},
  title = {An Ontology for Engineering Mathematics.},
  booktitle = { Proceedings of the 4th International Conference on Principles of Knowledge Representation and Reasoning (KR'94). Bonn, Germany, May 24-27, 1994.},
  publisher = {Morgan Kaufmann},
  year = {1994},
  pages = {258-269},
  url = {ftp://ftp.ksl.stanford.edu/pub/KSL_Reports/KSL-94-18.ps.gz}
}