Circus specifications define both data and behavioural aspects of systems using a combination of Z and CSP constructs. Previously, a denotational semantics has been given to Circus; however, a shallow embedding of Circus in Z, in which the mapping from Circus constructs to their semantic representation as a Z specification, with yet another language being used as a meta-language, was not useful for proving properties like the refinement laws that justify the distinguishing development technique associated with Circus. This work presents a final reference for the Circus denotational semantics based on Hoare and He’s Unifying Theories of Programming (UTP); as such, it allows the proof of meta-theorems about Circus including the refinement laws in which we are interested. Its correspondence with the CSP semantics is illustrated with some examples. We also discuss the library of lemmas and theorems used in the proofs of the refinement laws. Finally, we give an account of the mechanisation of the Circus semantics and of the mechanical proofs of the refinement laws.

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The increasing interest in the combination of different computational paradigms is well represented by Hoare and He in the Unifying Theories of Programming (UTP). In this paper, we present a mechanisation of part of that work in a theorem prover, ProofPower-Z; the theories of alphabetised relations, designs, reactive and CSP processes are in the scope of this paper. Furthermore, the mechanisation of Circus , a language that combines Z, CSP, specification statements and Dijkstra’s guarded command language, is also presented here. We also present an account of how this mechanisation is achieved, and more interestingly, of what issues were raised, and of our decisions. We aim at providing tool support not only for CSP and Circus , but also for further explorations of Hoare and He’s unification, and for the mechanisation of languages whose semantics is based on the UTP.

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