@incollection{Forbus83,
  author	= {Forbus, K. D.},
  editor	= {Gentner, D. and Stevens, A. L.},
  title		= {Qualitative reasoning about space and motion},
  booktitle	= {Mental models},
  publisher	= {Lawrence Erlbaum Associates},
  year		= {1983},
  address	= {Hillsdale, NJ}
}