1. R.J. Back. Correctness Preserving Program Refinements: Proof Theory and Applications, volume 131 of Mathematical Centre Tracts. Mathematical Centre, Amsterdam, 1980.
2. R.J. Back. A calculusof refinementsfor program derivations. Acta Informatica, 25:593–624, 1988.
3. .R.J. Back. Refinement diagrams. J. M. Morris and R. C. Shaw, editors, 4th Refinement Workshop, pages125–137, Cambridge, UK, January 1991. Springer-Verlag.
4. R.J. Back, L. Milovanov, I. Porres-Paltor and V. Preoteasa. A Case Study in Extreme Programming and Stepwise Feature Introduction. TUCS Technical Report, in preparation.
5. R.J. Back, L. Milovanov and V. Preoteasa. Testing layered software. TUCS Technical Report, in preparation.