Abstract. An impure language is one that combines functional and imperative constructs. We propose a method for ensuring termination of impure concurrent languages that makes it possible to combine term rewriting measure-based techniques with traditional approaches for termination in functional languages such as logical relations. The method can be made parametric on the termination technique employed on the functional part; it can also be iterated. We illustrate the method in the case of a π-calculus with both functional and imperative names, and show that, with respect to previous approaches to termination, it allows us to extend considerably the set of processes that can be handled. The method can also be applied to sequential languages, e.g., λ-calculi with references.

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International audienceWe describe an abstract machine, called GcPan, for the dis- tributed execution of Safe Ambients (SA), a variant of the Ambient Calculus (AC).Our machine improves over previous proposals for executing AC, or variants of it, mainly through a better management of special agents (forwarders), created upon code migration to transmit messages to the target location of the migration.We establish the correctness of our machine by proving a weak bisimilarity result with a previous abstract machine for SA, and then appealing to the correctness of the latter machine.More broadly, this study is a contribution towards understanding issues of correctness and optimisations in implementations of distributed languages encompassing mobility

Abstract. We give an axiomatisation of strong bisimilarity on a small fragment of CCS that does not feature the sum operator. This axiomatisation is then used to derive congruence of strong bisimilarity in the finite π-calculus in absence of sum. To our knowledge, this is the only nontrivial subcalculus of the π-calculus that includes the full output prefix and for which strong bisimilarity is a congruence.

We study the encoding of λ [] , the call by name λ-calculus enriched with McCarthy's amb operator, into the π-calculus. Semantically, amb is a challenging operator, for the fairness constraints that it expresses. We prove that, under a certain interpretation of divergence in the λ-calculus (weak divergence), a faithful encoding is impossible. However, with a different interpretation of divergence (strong divergence), the encoding is possible, and for this case we derive results and coinductive proof methods to reason about λ [] that are similar to those for the encoding of pure λ-calculi. We then use these methods to derive the most important laws concerning amb. We take bisimilarity as behavioural equivalence on the π-calculus, which sheds some light on the relationship between fairness and bisimilarity. As a spin-off result, we show that there is no small-step operational semantics for λ [] that preserves the branching structure of terms and yields the correct predicates of convergence and (weak) divergence.

This paper discusses an application of the higher-order abstract syntax technique to general-purpose theorem proving, yielding shallow embeddings of the binders of formalized languages. Higher-order abstract syntax has been applied with success in specialized logical frameworks which satisfy a closed-world assumption. As more general environments (like Isabelle/HOL or Coq) do not support this closed-world assumption, higher-order abstract syntax may yield exotic terms, that is, datatypes may produce more terms than there should actually be in the language. The work at hand demonstrates how such exotic terms can be eliminated by means of a two-level well-formedness predicate, further preparing the ground for an implementation of structural induction in terms of rule induction, and hence providing fully-fledged syntax analysis. In order to apply and justify well-formedness predicates, the paper develops a proof technique based on a combination of instantiations and reabstractions of higher-order terms. As an application, syntactic principles like the theory of contexts (as introduced by Honsell, Miculan, and Scagnetto) are derived, and adequacy of the predicates is shown, both within a formalization of the π-calculus in Isabelle/HOL.

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