Constructive characterisations of the must-preorder for asynchrony
Résumé
De Nicola and Hennessy's must-preorder is a contextual refinement which states that a server q refines a server p if all clients satisfied by p are also satisfied by q. Owing to the universal quantification over clients, this definition does not yied a practical proof method for the must-preorder, and alternative characterisations are necessary to reason on it.
We present the first characterisations of the must-preorder that are constructive, supported by a mechanisation in Coq, and independent from any calculus: our results pertain to Selinger output-buffered
agents with feedback. This is a class of Labelled Transition Systems that captures programs that communicate asynchronously via a shared unordered buffer, as in the asynchronous pi-calculus.
Our results are surprising: the behavioural characterisations devised for synchronous communication carry over as they stand to asynchronous communication, if servers are enhanced to act as forwarders,
i.e. they can input any message as long as they store it back into the shared buffer. This suggests a technique to port standard characterisations from synchronous to asynchronous settings.
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