1. Blumer, Herbert: Symbolic Interactionism (Prentice-Hall, New Jersey, 1969).
2. Fordham, Paul, Poulton, G. and Randle, L.: Learning Networks in Adult Education: Non-Formal Education on a Housing Estate (Routledge and Kegan Paul, 1979).
3. Glaser, B. G. and Strauss, A. L.: The Discovery of Grounded Theory (Weidenfeld and Nicolson, 1968).