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14
An Efficiency Preorder for Processes
"... A simple efficiency preorder for CCS processes is introduced, in which p ! q means that q is at least as fast as p, or more generally, p uses at least as much resources as q. It is shown to be preserved by all CCS contexts except summation and it is used to analyse a nontrivial example: differe ..."
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Cited by 70 (10 self)
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A simple efficiency preorder for CCS processes is introduced, in which p ! q means that q is at least as fast as p, or more generally, p uses at least as much resources as q. It is shown to be preserved by all CCS contexts except summation and it is used to analyse a nontrivial example: different implementations of a bounded buffer. Finally a sound and complete proof system for finite processes is given. This paper appeared earlier in [1] and [2]. This version of the paper has been revised, corrected and extended to include more operators, more examples and some additional remarks and observations by the first author. Hence all errors are entirely his responsiblity. Most of this work was done while the first author was at the University of Sussex and supported by SERC grant GR/D 97368 of the Science and Engineering Research Council of Great Britain. y The second author would like to acknowledge the support of ESPIRIT II. 1 Introduction A large number of behavioural equivale...
Bisimulation Congruences in Safe Ambients
 In 29th ACM Symposium on Principles of Programming Languages (POPL
, 2001
"... We study a variant of Levi and Sangiorgi's Safe Ambients (SA) enriched with passwords (SAP). In SAP by managing passwords, for example generating new ones and distributing them selectively, an ambient may now program who may migrate into its computation space, and when. Moreover in SAP an ambient ma ..."
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Cited by 54 (7 self)
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We study a variant of Levi and Sangiorgi's Safe Ambients (SA) enriched with passwords (SAP). In SAP by managing passwords, for example generating new ones and distributing them selectively, an ambient may now program who may migrate into its computation space, and when. Moreover in SAP an ambient may provide different services depending on the passwords exhibited by its incoming clients. We give an lts based operational semantics for SAP and a labelled bisimulation based equivalence which is proved to coincide with barbed congruence. Our notion of bisimulation is used to prove a set of algebraic laws which are subsequently exploited to prove more significant examples. 1
Bisimulations in the joincalculus
 Theoretical Computer Science
, 1998
"... We propose an objectoriented calculus with internal concurrency and classbased inheritance that is built upon the join calculus. Method calls, locks, and states are handled in a uniform manner, using asynchronous messages. Classes are partial message definitions that can be combined and transforme ..."
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Cited by 50 (6 self)
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We propose an objectoriented calculus with internal concurrency and classbased inheritance that is built upon the join calculus. Method calls, locks, and states are handled in a uniform manner, using asynchronous messages. Classes are partial message definitions that can be combined and transformed. We design operators for behavioral and synchronization inheritance. We also give a type system that statically enforces basic safety properties. Our model is compatible with the JoCaml implementation
Communication interference in mobile boxed ambients
 In FST & TCS
, 2002
"... communication primitives acting across ambient boundaries. Expressiveness is achieved at the price of communication interferences on message reception whose resolution requires synchronisation of activities at multiple, distributed locations. We study a variant of BA aimed at controlling communicati ..."
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Cited by 42 (7 self)
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communication primitives acting across ambient boundaries. Expressiveness is achieved at the price of communication interferences on message reception whose resolution requires synchronisation of activities at multiple, distributed locations. We study a variant of BA aimed at controlling communication interferences as well as mobility ones. Our calculus draws inspiration from Safe Ambients (SA) (with passwords) and modifies the communication mechanism of BA. Expressiveness is maintained through a new form of cocapability that at the same time registers incoming agents with the receiver ambient and performs access control.
Cyclic Lambda Calculi
, 1997
"... . We precisely characterize a class of cyclic lambdagraphs, and then give a sound and complete axiomatization of the terms that represent a given graph. The equational axiom system is an extension of lambda calculus with the letrec construct. In contrast to current theories, which impose restrictio ..."
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Cited by 36 (5 self)
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. We precisely characterize a class of cyclic lambdagraphs, and then give a sound and complete axiomatization of the terms that represent a given graph. The equational axiom system is an extension of lambda calculus with the letrec construct. In contrast to current theories, which impose restrictions on where the rewriting can take place, our theory is very liberal, e.g., it allows rewriting under lambdaabstractions and on cycles. As shown previously, the reduction theory is nonconfluent. We thus introduce an approximate notion of confluence. Using this notion we define the infinite normal form or L'evyLongo tree of a cyclic term. We show that the infinite normal form defines a congruence on the set of terms. We relate our cyclic lambda calculus to the traditional lambda calculus and to the infinitary lambda calculus. Since most implementations of nonstrict functional languages rely on sharing to avoid repeating computations, we develop a variant of our calculus that enforces the ...
Bisimulation Proof Methods for Mobile Ambients
 IN PROC. OF ICALP’03, VOLUME 2719 OF LNCS
, 2003
"... We study the behavioural theory of Cardelli and Gordon's Mobile Ambients. We give an LTS based operational semantics, and a labelled bisimulation based equivalence that coincides with reduction barbed congruence. We also provide two upto proof techniques that we use to prove a set of algebraic laws ..."
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Cited by 21 (3 self)
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We study the behavioural theory of Cardelli and Gordon's Mobile Ambients. We give an LTS based operational semantics, and a labelled bisimulation based equivalence that coincides with reduction barbed congruence. We also provide two upto proof techniques that we use to prove a set of algebraic laws, including the perfect firewall equation.
Relational Reasoning about Contexts
 HIGHER ORDER OPERATIONAL TECHNIQUES IN SEMANTICS, PUBLICATIONS OF THE NEWTON INSTITUTE
, 1998
"... ..."
Conformance: A Precongruence Close to Bisimilarity
 In STRICT ’95, Workshops in Comp
, 1995
"... In a previous paper we had dened the notion of an eciency preorder for concurrent systems. In this paper, we present a coarser relation, called the elaboration preorder, which is ner than observational equivalence. Further, this preorder is incomparable with the almostweak bismulation preorder of Mi ..."
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Cited by 16 (5 self)
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In a previous paper we had dened the notion of an eciency preorder for concurrent systems. In this paper, we present a coarser relation, called the elaboration preorder, which is ner than observational equivalence. Further, this preorder is incomparable with the almostweak bismulation preorder of Milner and Sangiorgi. In particular, the elaboration preorder is preserved under all contexts except summation. The largest precongruence contained in it, which we call conformance, is obtained by the usual means and a complete axiomatization for conformance of nite processes is given. The paper ends with an example to show the use of this relation. 1 Introduction In [1] the eciency preorder was dened on processes and a proof system was given and shown to be complete for nite processes. It was shown that it was possible to compare eciencies of dierent implementations of the same specication with little extra eort than that required to prove their correctness. However, the eciency preo...
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 improvement ..."
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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".
Unique Fixed Point Induction for McCarthy's Amb
 IN: PROCEEDINGS OF THE 24TH INTERNATIONAL SYMPOSIUM ON MATHEMATICAL FOUNDATIONS OF COMPUTER SCIENCE, ”LNCS” 1672
, 1999
"... We develop an operational theory of higherorder functions, recursion, and fair nondeterminism for a nontrivial, higherorder, callbyname functional programming language extended with McCarthy's amb. Implemented via fair parallel evaluation, functional programming with amb is very expressive. ..."
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Cited by 7 (2 self)
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We develop an operational theory of higherorder functions, recursion, and fair nondeterminism for a nontrivial, higherorder, callbyname functional programming language extended with McCarthy's amb. Implemented via fair parallel evaluation, functional programming with amb is very expressive. However, conventional semantic fixed point principles for reasoning about recursion fail in the presence of fairness. Instead, we adapt higherorder operational methods to deal with fair nondeterminism. We present two natural semantics, describing mayand mustconvergence, and define a notion of contextual equivalence over these two modalities. The presence of amb raises special difficulties when reasoning about contextual equivalence. In particular, we report on a challenging open problem with regard to the validity of bisimulation proof methods. We develop two sound and useful reasoning methods which, in combination, enable us to prove a rich collection of laws for contextual...