In: Brian Logan, Karl Millington, and Tim Smithers, 1991, Being Economical With the Truth: Assumption- Based Context Management in the Edinburgh Designer System, in John S Gero (Ed), Artificial Intelligence in Design ’91, Butterworth-Heinemann, 1991, pp 423– 446. Proceedings of the First International Conference on Artificial Intelligence in Design, Edinburgh, 25–27 June, 1991