1. Marr D (1982) Vision. Preeman, New York
2. Newell A (1981) The knowledge level. AI Magazine, summer 1–20
3. Mira J, Delgado AE, Boticario JG, Diez FJ (1995) Aspectos básicos de la in-teligencia artificial. Sanz y Torres, SL Madrid
4. Chomsky N.(1968) Language and Mind. Harcourt Brace & World Inc., N. York
5. Pylyshyn ZW (1986) Computation and cognition. Towards a foundation for cog-nitive science. The MIT Press. Cambridge, Mass