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The Fusion Calculus: Expressiveness and Symmetry in Mobile Processes (Extended Abstract)
 LICS'98
, 1998
"... We present the fusion calculus as a significant step towards a canonical calculus of concurrency. It simplifies and extends the πcalculus.
The fusion calculus contains the polyadic πcalculus as a proper subcalculus and thus inherits all its expressive power. The gain is that fusion contains action ..."
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Cited by 115 (13 self)
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We present the fusion calculus as a significant step towards a canonical calculus of concurrency. It simplifies and extends the πcalculus.
The fusion calculus contains the polyadic πcalculus as a proper subcalculus and thus inherits all its expressive power. The gain is that fusion contains actions akin to updating a shared state, and a scoping construct for bounding their effects. Therefore it is easier to represent computational models such as concurrent constraints formalisms. It is also easy to represent the so called strong reduction strategies in the lambdacalculus, involving reduction under abstraction. In the πcalculus these tasks require elaborate encodings.
The dramatic main point of this paper is that we achieve these improvements by simplifying the πcalculus rather than adding features to it. The fusion calculus has only one binding operator where the πcalculus has two (input and restriction). It has a complete symmetry between input and output actions where the πcalculus has not. There is only one sensible variety of bisimulation congruence where the picalculus has at least three (early, late and open). Proofs about the fusion calculus, for example in complete axiomatizations and full abstraction, therefore are shorter and clearer.
Our results on the fusion calculus in this paper are the following. We give a structured operational semantics in the traditional style. The novelty lies in a new kind of action, fusion actions for emulating updates of a shared state. We prove that the calculus contains the πcalculus as a subcalculus. We define and motivate the bisimulation equivalence and prove a simple characterization of its induced congruence, which is given two versions of a complete axiomatization for finite terms. The expressive power of the calculus is demonstrated by giving a straightforward encoding of the strong lazy lambdacalculus, which admits reduction under lambda abstraction.
Decoding Choice Encodings
, 1999
"... We study two encodings of the asynchronous #calculus with inputguarded choice into its choicefree fragment. One encoding is divergencefree, but refines the atomic commitment of choice into gradual commitment. The other preserves atomicity, but introduces divergence. The divergent encoding is ..."
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Cited by 100 (5 self)
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We study two encodings of the asynchronous #calculus with inputguarded choice into its choicefree fragment. One encoding is divergencefree, but refines the atomic commitment of choice into gradual commitment. The other preserves atomicity, but introduces divergence. The divergent encoding is fully abstract with respect to weak bisimulation, but the more natural divergencefree encoding is not. Instead, we show that it is fully abstract with respect to coupled simulation, a slightly coarserbut still coinductively definedequivalence that does not enforce bisimilarity of internal branching decisions. The correctness proofs for the two choice encodings introduce a novel proof technique exploiting the properties of explicit decodings from translations to source terms.
From SOS Rules to Proof Principles: An Operational Metatheory for Functional Languages
 In Proc. POPL'97, the 24 th ACM SIGPLANSIGACT Symposium on Principles of Programming Languages
, 1997
"... Structural Operational Semantics (SOS) is a widely used formalism for specifying the computational meaning of programs, and is commonly used in specifying the semantics of functional languages. Despite this widespread use there has been relatively little work on the imetatheoryj for such semantics. ..."
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Cited by 18 (1 self)
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Structural Operational Semantics (SOS) is a widely used formalism for specifying the computational meaning of programs, and is commonly used in specifying the semantics of functional languages. Despite this widespread use there has been relatively little work on the imetatheoryj for such semantics. As a consequence the operational approach to reasoning is considered ad hoc since the same basic proof techniques and reasoning tools are reestablished over and over, once for each operational semantics speciøcation. This paper develops some metatheory for a certain class of SOS language speciøcations for functional languages. We deøne a rule format, Globally Deterministic SOS (gdsos), and establish some proof principles for reasoning about equivalence which are sound for all languages which can be expressed in this format. More speciøcally, if the SOS rules for the operators of a language conform to the syntax of the gdsos format, then ffl a syntactic analogy of continuity holds, which rel...
Improvement Theory and its Applications
 HIGHER ORDER OPERATIONAL TECHNIQUES IN SEMANTICS, PUBLICATIONS OF THE NEWTON INSTITUTE
, 1997
"... An improvement theory is a variant of the standard theories of observational approximation (or equivalence) in which the basic observations made of a functional program's execution include some intensionalinformation about, for example, the program's computational cost. One program is an i ..."
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Cited by 10 (4 self)
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An improvement theory is a variant of the standard theories of observational approximation (or equivalence) in which the basic observations made of a functional program's execution include some intensionalinformation about, for example, the program's computational cost. One program is an improvement of another if its execution is more efficient in any program context. In this article we give an overview of our work on the theory and applications of improvement. Applications include reasoning about time properties of functional programs, and proving the correctness of program transformation methods. We also introduce a new application, in the form of some bisimulationlike proof techniques for equivalence, with something of the flavour of Sangiorgi's "bisimulation upto expansion and context".
Encoding Distributed Areas and Local Communication into the πCalculus
, 2002
"... We show how the #calculus can express local communications within a distributed system, through an encoding of the local area #calculus, an enriched system that explicitly represents names which are known universally but always refer to local information. Our translation replaces pointtopoint co ..."
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Cited by 4 (0 self)
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We show how the #calculus can express local communications within a distributed system, through an encoding of the local area #calculus, an enriched system that explicitly represents names which are known universally but always refer to local information. Our translation replaces pointtopoint communication with a system of shared local ethers; we prove that this preserves and reflects process behaviour.
Implicative Logic based encoding of the λcalculus into the πcalculus
, 2010
"... We study an outputbased encoding of the λcalculus with explicit substitution into the synchronous πcalculus – enriched with pairing – that has its origin in mathematical logic, and show that this encoding respects reduction. We will define the notion of (explicit) spine reductionwhich encompasse ..."
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Cited by 2 (1 self)
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We study an outputbased encoding of the λcalculus with explicit substitution into the synchronous πcalculus – enriched with pairing – that has its origin in mathematical logic, and show that this encoding respects reduction. We will define the notion of (explicit) spine reductionwhich encompasses (explicit) lazy reduction and show that the encoding fully encodes this reduction in that termsubstitution as well as each single reduction step are modelled up to contextual similarity. We show that all the main properties (soundness, completeness, and adequacy) hold for these four notions of reduction, as well as that termination is preserved. We then define a notion of type assignment for the πcalculus that uses the type constructor→, and show that all Curry types assignable to λterms are preserved by the encoding. Key words: the λcalculus, the πcalculus, intuitionistic logic, classical logic, encoding, type assignment
Relating Semantic Models for the Object Calculus
 In Proceedings of Express 97 Workshop, volume 7 of Electronic Notes in Theoretical Computer Science. Elsevier Science B.V
, 1997
"... Abadi and Cardelli have investigated several versions of the &calculus, a calculus for describing central features of objectoriented programs, with particular emphasis on various type systems. In this paper we study the properties of a denotational semantics due to Abadi and Cardelli vis`avi ..."
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Cited by 2 (2 self)
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Abadi and Cardelli have investigated several versions of the &calculus, a calculus for describing central features of objectoriented programs, with particular emphasis on various type systems. In this paper we study the properties of a denotational semantics due to Abadi and Cardelli vis`avis the notion of observational congruence for the calculus Ob 1!:¯ . In particular, we prove that the denotational semantics based on partial equivalence relations is correct with respect to observational congruence. By means of a counterexample, we argue that the denotational model is not fully abstract with respect to observational congruence. In fact, the model is able to distinguish objects that have the same behaviour in every Ob 1!:¯ context. 1 Introduction In [AC96] Abadi and Cardelli present and investigate several versions of the &calculus, a calculus for describing central features of objectoriented programs, with particular emphasis on various type systems. These object calculi ...
Communication Errors in the πCalculus are Undecidable
"... We present an undecidability proof of the notion of communication errors in the polyadic #calculus. The demonstration follows a general pattern of undecidability proofs  reducing a wellknown undecidable problem to the problem in question. We make use of an encoding of the #calculus into the ..."
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Cited by 1 (0 self)
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We present an undecidability proof of the notion of communication errors in the polyadic #calculus. The demonstration follows a general pattern of undecidability proofs  reducing a wellknown undecidable problem to the problem in question. We make use of an encoding of the #calculus into the #calculus to show that the decidability of communication errors would solve the problem of deciding whether a lambda term has a normal form.
Encoding Distributed Areas and Local Communication into the πCalculus
"... We show how the πcalculus can express local communications within a distributed system, through an encoding of the local area πcalculus, an enriched system that explicitly represents names which are known universally but always refer to local information. Our translation replaces pointtopoint co ..."
Abstract
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We show how the πcalculus can express local communications within a distributed system, through an encoding of the local area πcalculus, an enriched system that explicitly represents names which are known universally but always refer to local information. Our translation replaces pointtopoint communication with a system of shared local ethers; we prove that this preserves and reflects process behaviour. We give an example based on an internet service dæmon, and investigate some limitations of the encoding. 1