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18
Models for NamePassing Processes: Interleaving and Causal
 In Proceedings of LICS 2000: the 15th IEEE Symposium on Logic in Computer Science (Santa Barbara
, 2000
"... We study syntaxfree models for namepassing processes. For interleaving semantics, we identify the indexing structure required of an early labelled transition system to support the usual picalculus operations, defining Indexed Labelled Transition Systems. For noninterleaving causal semantics we de ..."
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Cited by 27 (3 self)
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We study syntaxfree models for namepassing processes. For interleaving semantics, we identify the indexing structure required of an early labelled transition system to support the usual picalculus operations, defining Indexed Labelled Transition Systems. For noninterleaving causal semantics we define Indexed Labelled Asynchronous Transition Systems, smoothly generalizing both our interleaving model and the standard Asynchronous Transition Systems model for CCSlike calculi. In each case we relate a denotational semantics to an operational view, for bisimulation and causal bisimulation respectively. We establish completeness properties of, and adjunctions between, categories of the two models. Alternative indexing structures and possible applications are also discussed. These are first steps towards a uniform understanding of the semantics and operations of namepassing calculi.
A Proof Search Specification of the πCalculus
 IN 3RD WORKSHOP ON THE FOUNDATIONS OF GLOBAL UBIQUITOUS COMPUTING
, 2004
"... We present a metalogic that contains a new quantifier (for encoding "generic judgment") and inference rules for reasoning within fixed points of a given specification. We then specify the operational semantics and bisimulation relations for the finite πcalculus within this metalogic ..."
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Cited by 21 (11 self)
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We present a metalogic that contains a new quantifier (for encoding "generic judgment") and inference rules for reasoning within fixed points of a given specification. We then specify the operational semantics and bisimulation relations for the finite πcalculus within this metalogic. Since we
Proof search specifications of bisimulation and modal logics for the πcalculus
 ACM Trans. on Computational Logic
"... We specify the operational semantics and bisimulation relations for the finite πcalculus within a logic that contains the ∇ quantifier for encoding generic judgments and definitions for encoding fixed points. Since we restrict to the finite case, the ability of the logic to unfold fixed points allo ..."
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Cited by 14 (9 self)
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We specify the operational semantics and bisimulation relations for the finite πcalculus within a logic that contains the ∇ quantifier for encoding generic judgments and definitions for encoding fixed points. Since we restrict to the finite case, the ability of the logic to unfold fixed points allows this logic to be complete for both the inductive nature of operational semantics and the coinductive nature of bisimulation. The ∇ quantifier helps with the delicate issues surrounding the scope of variables within πcalculus expressions and their executions (proofs). We shall illustrate several merits of the logical specifications permitted by this logic: they are natural and declarative; they contain no sideconditions concerning names of variables while maintaining a completely formal treatment of such variables; differences between late and open bisimulation relations arise from familar logic distinctions; the interplay between the three quantifiers (∀, ∃, and ∇) and their scopes can explain the differences between early and late bisimulation and between various modal operators based on bound input and output actions; and proof search involving the application of inference rules, unification, and backtracking can provide complete proof systems for onestep transitions, bisimulation, and satisfaction in modal logic. We also illustrate how one can encode the πcalculus with replications, in an extended logic with induction and coinduction.
Mixing finite success and finite failure in an automated prover
 In Proceedings of ESHOL’05: Empirically Successful Automated Reasoning in HigherOrder Logics, pages 79 – 98
, 2005
"... Abstract. The operational semantics and typing judgements of modern programming and specification languages are often defined using relations and proof systems. In simple settings, logic programming languages can be used to provide rather direct and natural interpreters for such operational semantic ..."
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Cited by 14 (7 self)
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Abstract. The operational semantics and typing judgements of modern programming and specification languages are often defined using relations and proof systems. In simple settings, logic programming languages can be used to provide rather direct and natural interpreters for such operational semantics. More complex features of specifications such as names and their bindings, proof rules with negative premises, and the exhaustive enumeration of state spaces, all pose significant challenges to conventional logic programming systems. In this paper, we describe a simple architecture for the implementation of deduction systems that allows a specification to interleave between finite success and finite failure. The implementation techniques for this prover are largely common ones from higherorder logic programming, i.e., logic variables, (higherorder pattern) unification, backtracking (using streambased computation), and abstract syntax based on simply typed λterms. We present a particular instance of this prover’s architecture and its prototype implementation, Level 0/1, based on the dual interpretation of (finite) success and finite failure in proof search. We show how Level 0/1 provides a highlevel and declarative implementation of model checking and bisimulation checking for the (finite) πcalculus. 1
Symbolic Bisimulations and Proof Systems for the πCalculus
 PROC. 17TH ACM STOC,327{334(1985
, 1994
"... A theory of symbolic bisimulation for the πcalculus is proposed which captures the conventional notions of bisimulationbased equivalences for this calculus. Proof systems are presented for both late and early equivalences, and their soundness and completeness are proved. The proof system for early ..."
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Cited by 11 (1 self)
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A theory of symbolic bisimulation for the πcalculus is proposed which captures the conventional notions of bisimulationbased equivalences for this calculus. Proof systems are presented for both late and early equivalences, and their soundness and completeness are proved. The proof system for early equivalence differs from that for late equivalence only in the inference rule for input prefixing. For the version of πcalculus extended with the mismatch construction, complete proof systems can be obtained by adding a rule for mismatch to the proof systems for the πcalculus proper.
A Fully Abstract Symbolic Semantics for PsiCalculi
"... We present a symbolic transition system and bisimulation equivalence for psicalculi, and show that it is fully abstract with respect to bisimulation congruence in the nonsymbolic semantics. A psicalculus is an extension of the picalculus with nominal data types for data structures and for logica ..."
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Cited by 10 (6 self)
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We present a symbolic transition system and bisimulation equivalence for psicalculi, and show that it is fully abstract with respect to bisimulation congruence in the nonsymbolic semantics. A psicalculus is an extension of the picalculus with nominal data types for data structures and for logical assertions representing facts about data. These can be transmitted between processes and their names can be statically scoped using the standard picalculus mechanism to allow for scope migrations. Psicalculi can be more general than other proposed extensions of the picalculus such as the applied picalculus, the spicalculus, the fusion calculus, or the concurrent constraint picalculus. Symbolic semantics are necessary for an efficient implementation of the calculus in automated tools exploring state spaces, and the full abstraction property means the semantics of a process does not change from the original. 1
Tau laws for pi calculus
 Theoretical Computer Science
"... The paper investigates the nonsymbolic algebraic semantics of the weak bisimulation congruences on finite pi processes. The weak bisimulation congruences are studied both in the absence and in the presence of the mismatch operator. Some interesting phenomena about the open congruences are revealed. ..."
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Cited by 10 (4 self)
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The paper investigates the nonsymbolic algebraic semantics of the weak bisimulation congruences on finite pi processes. The weak bisimulation congruences are studied both in the absence and in the presence of the mismatch operator. Some interesting phenomena about the open congruences are revealed. Several new tau laws are discovered and their relationship is discussed. The contributions of the paper are mainly as follows: 1. It is proved that Milner’s three tau laws fail to lift a complete system for the strong open congruence to a complete system for the weak open congruence in the absence of both the mismatch operator and the restriction operator. A fourth tau law is proposed to deal with the match operator under the prefix operation. It is shown that for this calculus a complete system for the strong open congruence extended with all the four tau laws is complete for the weak open congruence. 2. It is verified that the four tau laws are also enough for the weak open congruence of the pi calculus without the mismatch operator. Two complete systems are given, one using distinctions and the other using a schematic law for the restriction operator.
Model checking for nominal calculi
 IN FOSSACS, VOLUME 3441 OF LNCS
, 2005
"... Nominal calculi have been shown very effective to formally model a variety of computational phenomena. The models of nominal calculi have often infinite states, thus making model checking a difficult task. In this note we survey some of the approaches for model checking nominal calculi. Then, we f ..."
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Cited by 10 (3 self)
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Nominal calculi have been shown very effective to formally model a variety of computational phenomena. The models of nominal calculi have often infinite states, thus making model checking a difficult task. In this note we survey some of the approaches for model checking nominal calculi. Then, we focus on HistoryDependent automata, a syntaxfree automatonbased model of mobility. HistoryDependent automata have provided the formal basis to design and implement some existing verification toolkits. We then introduce a novel syntaxfree setting to model the symbolic semantics of a nominal calculus. Our approach relies on the notions of reactive systems and observed borrowed contexts introduced by Leifer and Milner, and further developed by Sassone, Lack and Sobocinski. We argue that the symbolic semantics model based on borrowed contexts can be conveniently applied to web service discovery and binding.
Representing and reasoning with operational semantics
 In: Proceedings of the Joint International Conference on Automated Reasoning
, 2006
"... The operational semantics of programming and specification languages is often presented via inference rules and these can generally be mapped into logic programminglike clauses. Such logical encodings of operational semantics can be surprisingly declarative if one uses logics that directly account ..."
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Cited by 8 (2 self)
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The operational semantics of programming and specification languages is often presented via inference rules and these can generally be mapped into logic programminglike clauses. Such logical encodings of operational semantics can be surprisingly declarative if one uses logics that directly account for termlevel bindings and for resources, such as are found in linear logic. Traditional theorem proving techniques, such as unification and backtracking search, can then be applied to animate operational semantic specifications. Of course, one wishes to go a step further than animation: using logic to encode computation should facilitate formal reasoning directly with semantic specifications. We outline an approach to reasoning about logic specifications that involves viewing logic specifications as theories in an objectlogic and then using a metalogic to reason about properties of those objectlogic theories. We motivate the principal design goals of a particular metalogic that has been built for that purpose.
On Compositional Reasoning in the Spicalculus
 In Proc. of the 5th International Conference on Foundations of Software Science and Computation Structures (FossaCS’02), volume 2303 of LNCS
, 2002
"... Observational equivalences can be used to reason about the correctness of security protocols described in the spicalculus. Unlike in CCS or in #calculus, these equivalences do not enjoy a simple formulation in spicalculus. The present paper aims at enriching the set of tools for reasoning on proc ..."
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Cited by 7 (1 self)
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Observational equivalences can be used to reason about the correctness of security protocols described in the spicalculus. Unlike in CCS or in #calculus, these equivalences do not enjoy a simple formulation in spicalculus. The present paper aims at enriching the set of tools for reasoning on processes by providing a few equational laws for a sensible notion of spibisimilarity. We discuss the di#culties underlying compositional reasoning in spicalculus and show that, in some cases and with some care, the proposed laws can be used to build compositional proofs. A selection of these laws forms the basis of a proof system that we show to be sound and complete for the strong version of bisimilarity.