1. Dijkstra, E.W.: ‘Why correctness must be a mathematical concern’, Boyer, R.S., Moore, J.S, (Academic PressThe correct-ness problem in computer science, 1981)
2. Hofstadter, D.R.: (Basic BooksGoder, Escher, Bach, 1979)
3. Jones, C.B.: (Prentice-HallSoftware development: A rigorous approach, 1980)
4. Sufrin, B.: (PRG Monograph 21, Oxford University PressFormal specification of a display editor, 1981)