Specification of a Program Derivation Editor

In this paper, a tool for structuring and manipulating formal program derivations is specified using the Z notation. A program derivation style based on (transitive) relations between programs, as found in the refinement calculus, is assumed. The structuring and manipulation of derivations is based on the notion of refinement diagrams proposed by Back. This allows for a style of derivation that is much more flexible than top-down refinement and is more suited to large-scale program development. The original refinement diagram notion is also extended with ideas from window inference which provides a powerful way of dealing with the use of different relations in sub-derivations