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2. http://www.thevisionssystem.com
3. Beukelman, D., Mirenda, P.; Augmentative and Alternative Communication (second edition), Brookes, 1998
4. Fischer, G.; User Modeling in Human-Computer Interaction, User Modeling and User-Adapted Interaction 11(1–2): 65–86, 2001
5. Gorman, A, Sullivan, J (2003) http://www.cs.colorado.edu/~l3d/clever/projects