1. UNIX Mail Reference Manual, Digital Equipment Corporation.
2. The trouble with UNIX;Norman;Datamation,1981
3. Lewis, C.: Using the “thinking-aloud” method in cognitive interface design. IBM Research Report RC 9265, IBM T.J. Watson Research Center, Yorktown Heights, New York, Feb. 1982.
4. O'Malley, C., Draper, S. and Riley, M.: Constructive Interaction: A method for studying user-computer interaction. In Proc. Interact′87, London, Sep. 1984, 1–5.
5. Mack, R.L.: Verbal protocol analysis comes of age. IBM Research Report RC 10655, IBM T.J. Watson Research Center Yorktown Heights, New York, Aug. 1984.