@techreport{Carr,
  author	= {Carr, B. and Goldstein, I.},
  month		= feb,
  year		= {1977},
  title		= {Overlays: A Theory of Modeling for Computer Aided Instruction},
  number	= {406},
  institution	= {Massachusetts Institute of Technology, Artificial Intelligence Laboratory},
  type		= {Memo}
}