Unfold/fold Transformations of Concurrent Processes 1

Program transformation is a technique for obtaining, starting from a program P, a semantically equivalent one, which is "better" than P with respect to a particular goal. Traditionally, the main goal of program transformation was obtaining more eecient programs, but, in general, this technique can be used to produce programs written in a syntactic form satisfying some properties. Program transformation techniques have been extensively studied in the framework of functional and logic languages, where they were applied mainly to obtain more eecient and readable programs. All these works are based on the Unfold/Fold program transformation method developed by Burstall and Darlington in the context of their recursive equational language. The use of Un-fold/Fold based transformations for concurrent languages is a relevant issue that has not yet received an adequate attention. In fact the existing proposals of transformations of concurrent programs are not based on a general Unfold/Fold transformation theory. The aim of this paper is to deene such a theory for the concurrent calculus CCS and to prove it correct.