14. NILSSON, N.J., Learning Machines - Foundations of Trainable Pattern Classifying Systems, McGraw-Hill, New York (1965).

15. ROCCHIO, J.J., 'Document retrieval systems - Optimization and evaluation', Ph.D. Thesis, Harvard University, Report ISR-10 to National Science Foundation, Harvard Computation Laboratory (1966).

16. LANCASTER, F.W. and FAYEN, E.G., Information Retrieval On-line, Melville Publishing Co., Los Angeles, California (1973).

17. BARRACLOUGH, E.D., "On-line searching in information retrieval', Journal of Documentation, 33, 220-238 (1977).

18. VERHOEFF, J., GOFFMAN, W. and BELZER, J., 'Inefficiency of the use of boolean functions for information retrieval systems', Communications of the ACM, 4, 557-558, 594 (1961).

19. MILLER, W.L., 'A probabilistic search strategy for MEDLARS', Journal of Documentation, 17, 254-266 (1971).

20. ANGIONE, P.V., 'On the equivalence of Boolean and weighted searching based on the convertibility of query forms', Journal of the American Society for Information Science, 26, 112-124 (1975).

21. RICKMAN, J.T., 'Design consideration for a Boolean search system with automatic relevance feedback processing', Proceedings of the ACM 1972 Annual Conference, 478-481 (1972).

22. GOFFMAN, W., 'An indirect method of information retrieval', Information Storage and Retrieval, 4, 361-373 (1969).

23. HYVARINEN, L., 'Classification of qualitative data', BIT, Nordisk Tidskrift för Informationsbehandling, 2, 83-89 (1962).

24. NEGOITA, C.V., 'On the decision process in information retrieval', Studii si cercetari de documentare, 15, 269-281 (1973).

25. SALTON, G., The SMART Retrieval System - Experiment in Automatic Document Processing, Prentice-Hall, Englewood Cliffs, New Jersey (1971).

26. STANFEL, L.E., 'Sequential adaptation of retrieval systems based on user inputs', Information Storage and Retrieval, 7, 69-78 (1971).

27. BONO, P.R., 'Adaptive procedures for automatic document retrieval', Ph.D. Thesis, University of Michigan (1972).