An Alternative Semantics for the Parallel Operator of the Calculus of Gamma Programs

The Gamma model is a minimal programming notation based on the chemical reaction metaphor. Hankin, Le M etayer, and Sands derived a Calculus of Gamma Programs adding two operators to the notation: the parallel and sequential composition operators. In this paper we address some compositional problems due to the semantics of the parallel operator for which we propose an alternative semantics as a solution to these problems. The semantics of the new version of the calculus is also deened by means of a labeled transition system. This permits the deenition of some observational equivalences. We introduce two of them using the concept of bisimulation. The equivalences are proved to be congruences and are characterized by means of sound and complete axiomatizations.