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- Why should I believe that your program is correct?
- Formal model of the specification.
- Designed model system such that some invariants are maintained.
- Can reason that invariants imply specification.
- Code is implementation of the model system.

- But you have not verified your allegations in detail.
- With more efforts (costs), reasoning can be refined.
- Show that model system indeed maintains invariants.
- Refine invariants such that they indeed imply specification.
- Show that implementation preserves properties of model.

*Design process increases confidence and supports further analysis.*

Author: Wolfgang Schreiner

Last Modification: April 22, 1999