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26
Hereditary History Preserving Simulation is Undecidable
, 1999
"... We show undecidability of hereditary history preserving simulation for finite asynchronous transition systems by a reduction from the halting problem of deterministic Turing machines. To make the proof more transparent we introduce an intermediate problem of deciding the winner in domino snake games ..."
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We show undecidability of hereditary history preserving simulation for finite asynchronous transition systems by a reduction from the halting problem of deterministic Turing machines. To make the proof more transparent we introduce an intermediate problem of deciding the winner in domino snake games. First we reduce the halting problem of deterministic Turing machines to domino snake games. Then we show how to model a domino snake game by a hereditary history simulation game on a pair of finite asynchronous transition systems.
Two Notes on the Computational Complexity of OneDimensional Sandpiles
"... We prove that the onedimensional sandpile prediction problem is . The previously best known upper bound on the AC scale was AC . We also prove that it is not in AC for any constant > 0. ..."
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We prove that the onedimensional sandpile prediction problem is . The previously best known upper bound on the AC scale was AC . We also prove that it is not in AC for any constant > 0.
Northeastern University
"... Abstract. We present a sound and complete method for reasoning about contextual equivalence in the untyped, imperative object calculus of Abadi and Cardelli [1]. Our method is based on bisimulations, following the work of Sumii and Pierce [25, 26] and our own [14]. Using our method we were able to p ..."
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Abstract. We present a sound and complete method for reasoning about contextual equivalence in the untyped, imperative object calculus of Abadi and Cardelli [1]. Our method is based on bisimulations, following the work of Sumii and Pierce [25, 26] and our own [14]. Using our method we were able to prove equivalence in more complex examples than the ones of Gordon, Hankin and Lassen [7] and Gordon and Rees [8]. We can also write bisimulations in closed form in cases where similar bisimulation methods [26] require an inductive specification. To derive our bisimulations we follow the same technique as we did in [14], thus indicating the extensibility of this method. 1
A πcalculus process semantics of concurrent idealised ALGOL
 In Proc. FOSSACS'99, volume 1578 of LNCS
, 1999
"... We study the use of the πcalculus for semantical descriptions of languages such as Concurrent Idealised ALGOL (CIA), combining imperative, functional and concurrent features. We first present an operational semantics for CIA, given by SOS rules and a contextual form of behavioural equivalence; th ..."
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We study the use of the πcalculus for semantical descriptions of languages such as Concurrent Idealised ALGOL (CIA), combining imperative, functional and concurrent features. We first present an operational semantics for CIA, given by SOS rules and a contextual form of behavioural equivalence; then a πcalculus semantics. As behavioural equivalence on πcalculus processes we choose the standard (weak early) bisimilarity. We compare the two semantics, demonstrating that there is a close operational correspondence between them and that the πcalculus semantics is sound. This allows for applying thecalculus theory in proving behavioural properties of CIA phrases. We discuss laws and examples which have served as benchmarks to various semantics, and a more complex example involving procedures of higher order.
Mobile Objects as Mobile Processes
, 2001
"... this paper, we rewrite our modified semantics of jeblik in terms of the #calculus, and we use it to formally prove the correctness of object surrogation, the abstraction of object migration in jeblik. Key Words: #calculus, Objects, Migration 1. ..."
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this paper, we rewrite our modified semantics of jeblik in terms of the #calculus, and we use it to formally prove the correctness of object surrogation, the abstraction of object migration in jeblik. Key Words: #calculus, Objects, Migration 1.
Responsive Bisimulation
 In Proceedings of the 2nd IFIP InternationalConference on Theoretical Computer Science
, 2002
"... This paper introduces the responsive bisimulation, which treats local delays of incoming messages the same as external delays, as long as potential interference by competing receptors is avoided. By this bisimulation, the calculus process , representing a lock with a message receptor , is ..."
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This paper introduces the responsive bisimulation, which treats local delays of incoming messages the same as external delays, as long as potential interference by competing receptors is avoided. By this bisimulation, the calculus process , representing a lock with a message receptor , is equivalent to the 22824 ; the first process will delay messages externally, the second locally. Existing bisimulations distinguish between these processes. The responsive bisimulation is a congruence for the family of processes which model objects. It is useful for studying compositional synchronisation in such models. 1.
An Interpretation of Typed Concurrent Objects in the Blue Calculus
 In Proceedings of the Conference on Empirical Methods in Natural Language Pr ocessing
, 1999
"... We propose an interpretation of a typed concurrent calculus of objects (conc&) based on the model of Abadi and Cardelli's imperative object calculus. The target of our interpretation is a version of the blue calculus, a variant of the picalculus that directly contains the lambdacalculus, with reco ..."
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We propose an interpretation of a typed concurrent calculus of objects (conc&) based on the model of Abadi and Cardelli's imperative object calculus. The target of our interpretation is a version of the blue calculus, a variant of the picalculus that directly contains the lambdacalculus, with record and firstorder types. We show that reduction and type judgements can be derived in a rather simple and natural way, and that our encoding can be extended to "selftypes" and synchronisation primitives. We also prove some equational laws on objects.
Concurrent Objects in the Blue Calculus
, 1998
"... . We describe a model of concurrent objects based on the blue calculus ( ? ), a typed variant of the asynchronous calculus in which the notion of function is directly embedded. We propose a definition for a simple concurrent objectbased calculus and show how objects can be translated in ? . W ..."
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. We describe a model of concurrent objects based on the blue calculus ( ? ), a typed variant of the asynchronous calculus in which the notion of function is directly embedded. We propose a definition for a simple concurrent objectbased calculus and show how objects can be translated in ? . We also present the type system for objects derived from our definition and we verify the expressiveness of the object calculus by giving a direct and adequate interpretation of Abadi and Cardelli object calculus: Ob1!: , that preserves subtyping. 1 Introduction In his article [21], Milner states that the reduction relation of the calculus () is based on the object paradigm, in the sense that "what is transmitted and bound is never an object, but rather access to the object". There is a strong connection with objectoriented programming here: processes are objects (and states), and communication channels are the references used to name/access objects. But the objectoriented paradigm is mor...
Surrogates in Øjeblik: Towards Migration in Obliq
 In H. Huttel and U. Nestmann, eds, Proceedings of SOAP '98, volume NS985 of BRICS Notes Series
, 1998
"... In Cardelli's lexically scoped, distributed, objectbased programming language Obliq, object migration was suggested as creating a (remote) copy of an objects' state at the target site, followed by turning the (local) object itself into a surrogate, i.e. a pointer to the just created remote copy. Th ..."
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In Cardelli's lexically scoped, distributed, objectbased programming language Obliq, object migration was suggested as creating a (remote) copy of an objects' state at the target site, followed by turning the (local) object itself into a surrogate, i.e. a pointer to the just created remote copy. This kind of migration is only safemigrated objects shall behave the same before and after migrationif it is protected and serialized. Protected objects can only be accessed by clients via selection, and within a serialized object at most one method can be active at any time. Yet, since Obliq does not have a formal semantics, there is no proof of this claim. In this abstract, we consider the act of creating object surrogates as an abstraction of the abovementioned style of migration. We introduce the language Øjeblik, a simplified distributionfree subset of Obliq, and give its formal semantics in terms of an encoding into the ßcalculus. This semantics shall provide the ground for pr...