1. Back R.J.R.: “A calculus of refinements for program derivations”, Acta Informatica
25, pp 593–624, 1988.
2. Chen, W. and Udding, J.T., “Towards a Calculus of Data Refinement”, Computing Science Notes CS8902, Dept. of Mathematics and Computing Science, Groningen University, Groningen, The Netherlands, 1989.
3. Dahl, O.-J., Dijkstra, E.W. and Hoare, C.A.R.: Structured Programming, Academic Press, London and New York, 1972.
4. Dijkstra, E.W.: A Discipline of Programming, Prentice-Hall, Englewood Cliffs, NJ, 1976.
5. Dijkstra, E.W.: “Extreme solutions of equation(draft of ch.5)”, EWD 912, UT at Austin, Texas, 1985.