1. Brajnik, G., G. Guida, and C. Tasso: 1990, ?User modeling in expert man-machine interfaces: a case study in intelligent information retrieval?.IEEE Trans. on Systems, Man and Cybernetics,20(1), 166?185.
2. Brajnik, G. and C. Tasso: 1992, ?A flexible tool for developing user modelling applications with non-monotonic reasoning capabilities?. In: E. Andre, R. Cohen, W. Graf, B. Kass, C. Paris and W. Wahlster (eds.):Proc. of UM92: Third International Workshop on User Modeling, pp. 42?66, Deutsches Forschungszentrum fur Kunstliche Intelligenz.
3. Brown, J. S., R. R. Burton and K. M. Larkin: 1977, ?Representing and using procedural bugs for educational purposes?.Proc. Annual Conference ACM, pp. 247?255, Seattle.
4. Browne, D., P. Totterdell and M. Norman: 1990. In:Adaptive user interfaces, Academic Press, San Diego, California.
5. Bullock, A. and O. Stallybrass: 1977. In:The Fontana Dictionary of Modern Thought.