Search

We consider bisimulation-invariant monadic second-order logic over various classes of finite transition systems. We present several combinatorial characterisations of when the expressive power of this fragment coincides with that of the modal μ -calculus. Using these characterisations we prove for some simple classes of transition systems that this is indeed the case. In particular, we show that, over the class of all finite transition systems with Cantor–Bendixson rank at most k , bisimulation-invariant Image 1 coincides with L μ. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of verifying heap evolution properties of pointer programs. To this end, a new unified model checking approach with MSVL (Modeling, Simulation and Verification Language) and PPTLSL is presented. The former is an executable subset of PTL (Projection Temporal Logic) while the latter is an extension of PPTL (Propositional Projection Temporal Logic) with separation logic. MSVL is used to model pointer programs, and PPTLSL to specify heap evolution properties. Technically, on one hand, models of MSVL programs are characterized by Normal Form Graphs (NFGs). On the other hand, PPTLSL is equisatisfiably reduced to its subset which can reuse the decision procedure of PPTL. Our technique is able to deal with a variety of pointer structures such as linked lists and composite structures. In addition, we implement a prototype tool by using an SMT solver as the verification engine in order to demonstrate our approach. [ABSTRACT FROM AUTHOR]

To specify and verify the concurrent and reactive systems with the theorem proving approach, a complete axiomatization is formalized for first order projection temporal logic (PTL) with both finite and infinite time. To this end, PTL is restricted to a finite domain, and the syntax, semantics as well as the axiomatization of PTL are presented. Further, the techniques of labeled normal form and labeled normal form graph of PTL formulas are introduced respectively, with which a decision procedure for quantifier free PTL (QFPTL) formulas is given. Moreover, a generalized labeled normal form graph is defined and employed to transform a quantified PTL formula into its equivalent QFPTL formula. Finally, a decision procedure for PTL is formalized and the completeness of the axiomatic system is proved based on the decidability of PTL formulas. [ABSTRACT FROM AUTHOR]

A binary decision diagram (BDDs) is a compact data structure used to represent a Boolean function, which facilitates scalable constructions of Boolean functions using reversible logic gates. Motivated by the scalable synthesis approach, this paper proposes an effective scheme for transforming the BDD representation of a Boolean function into a reversible circuit composed by reversible logic elements. Unlike a logic gate, a reversible logic element carries a memory to record a finite number of states. Especially, logic circuits composed by reversible elements can operate in asynchronous mode, thereby no need of a clock signal to drive all elements operating simultaneously. [ABSTRACT FROM AUTHOR]

Temporal logic has become essential for various areas in computer science, most notably for the specification and verification of hardware and software systems. For the specification purposes rich temporal languages are required that, in particular, can express fairness constraints. For linear-time logics which deal with fairness in the linear-time setting, one-pass and two-pass tableau methods have been developed. In the repository of the CTL-type branching-time setting, the well-known logics ECTL and ECT L + were developed to explicitly deal with fairness. However, due to the syntactical restrictions, these logics can only express restricted versions of fairness. The logic CT L ⋆ , often considered as 'the full branching-time logic' overcomes these restrictions on expressing fairness. However, CT L ⋆ is extremely challenging for the application of verification techniques, and the tableau technique, in particular. For example, there is no one-pass tableau construction for CT L ⋆ , while one-pass tableau has an additional benefit enabling the formulation of dual sequent calculi that are often treated as more 'natural' being more friendly for human understanding. These two considerations lead to the following problem - are there logics that have richer expressiveness than ECT L + , allowing the formulation of a new range of fairness constraints with 'until' operator, yet 'simpler' than CT L ⋆ , and for which a one-pass tableau can be developed? Here we give a positive answer to this question, introducing a sub-logic of CT L ⋆ called ECT L # , its tree-style one-pass tableau, and an algorithm for obtaining a systematic tableau, for any given admissible branching-time formulae. We prove the termination, soundness and completeness of the method. As tree-shaped one-pass tableaux are well suited for the automation and are amenable for the implementation and for the formulation of sequent calculi. Our results also open a prospect of relevant developments of the automation and implementation of the tableau method for ECT L # , and of a dual sequent calculi. [ABSTRACT FROM AUTHOR]

In this paper, we build a logic which is named N-sequent calculus. Based on this logic, we provide two kinds of logical representations of Lawson compact algebraic L-domains: one in terms of logical algebras and the other in terms of logical syntax. The first representation takes the corresponding logical algebras as research objects. The use of prime filters achieves the connection between our logic and Lawson compact algebraic L-domains. This approach is inspired by Abramsky's SFP domain logic and the disjunctive propositional logic on algebraic L-domains introduced by Yixiang Chen and Achim Jung. However, there are essential differences between them at the morphisms part. For the second representation, we directly adopt N-sequent calculi themselves as objects instead of the logical algebras. Then we establish the category of N-sequent calculi with consequence relations equivalent to that of Lawson compact algebraic L-domains with Scott continuous maps. This demonstrates the capability of the syntax of the logic in representing domains. [ABSTRACT FROM AUTHOR]

In the last years, some extensions of ω -regular languages, namely, ωB -regular (ω -regular languages extended with boundedness), ωS -regular (ω -regular languages extended with strong unboundedness), and ωBS -regular languages (the combination of ωB - and ωS -regular ones), have been proposed in the literature. While the first two classes satisfy a generalized closure property, which states that the complement of an ωB -regular (resp., ωS -regular) language is an ωS -regular (resp., ωB -regular) one, the last class is not closed under complementation. The existence of non- ωBS -regular languages that are the complements of some ωBS -regular ones and express fairly natural asymptotic behaviors motivates the search for other significant classes of extended ω -regular languages. In this paper, we present the class of ωT -regular languages, which includes meaningful languages that are not ωBS -regular. We define this new class of languages in terms of ωT -regular expressions. Then, we introduce a new class of automata (counter-check automata) and we prove that (i) their emptiness problem is decidable in PTIME, and (ii) they are expressive enough to capture ωT -regular languages. We also provide an encoding of ωT -regular expressions into S1S + U. Finally, we investigate a stronger variant of ωT -regular languages (ω T s -regular languages). We characterize the resulting class of languages in terms of ω T s -regular expressions, and we show how to map it into a suitable class of automata, called counter-queue automata. We conclude the paper with a comparison of the expressiveness of ωT - and ω T s -regular languages and of the corresponding automata. [ABSTRACT FROM AUTHOR]

Hybrid branching-time logics are a powerful extension of branching-time logics like CTL, CTL⁎ or even the modal μ -calculus through the addition of binders, jumps and variable tests. Their expressiveness is not restricted by bisimulation-invariance anymore. Hence, they do not retain the tree model property, and the finite model property is equally lost. Their satisfiability problems are typically undecidable, their model checking problems (on finite models) are decidable with complexities ranging from polynomial to non-elementary time. In this paper we study the expressive power of such hybrid branching-time logics. We extend the hierarchy of branching-time logics CTL, CTL+, CTL⁎ and the modal μ -calculus to their hybrid extensions. We show that most separation results can be transferred to the hybrid world, even though the required techniques become more involved. We also present collapse results for linear, tree-shaped and finite models. [ABSTRACT FROM AUTHOR]

We provide a proofs-as-concurrent-programs interpretation for a large class of intermediate logics that can be formalized by cut-free hypersequent calculi. Obtained by adding classical disjunctive tautologies to intuitionistic logic, these logics are used to type concurrent λ -calculi by Curry–Howard correspondence; each of the calculi features a specific communication mechanism, enhanced expressive power when compared to the λ -calculus, and implements forms of code mobility. We thus confirm Avron's 1991 thesis that intermediate logics formalizable by hypersequent calculi can serve as basis for concurrent λ -calculi. [ABSTRACT FROM AUTHOR]

We investigate the succinctness gap between two known equally-expressive and different linear-past extensions of standard ATL ⁎ . We establish by formal non-trivial arguments that the 'memoryful' linear-past extension (the history leading to the current state is taken into account) can be exponentially more succinct than the standard 'local' linear-past extension (the history leading to the current state is forgotten). As a second contribution, we consider the ATL -like fragment, denoted ATL l p , of the known 'memoryful' linear-past extension of ATL ⁎ . We show that ATL l p is strictly more expressive than ATL , and interestingly, it can be exponentially more succinct than the more expressive logic ATL ⁎. Moreover, we prove that both satisfiability and model-checking for the logic ATL l p are Exptime -complete. [ABSTRACT FROM AUTHOR]

We show how to represent polynomial time computation in an untyped version of proof-nets for elementary linear logic. This follows previous work by P. Baillot but which was developed in a typed and affine setting. We describe how these two properties can be adapted. [ABSTRACT FROM AUTHOR]

Several type systems have been proposed to statically control the time complexity of lambda-calculus programs and characterize complexity classes such as FPTIME or FEXPTIME. A first line of research stems from linear logic and restricted versions of its !-modality controlling duplication. An instance of this is light linear logic for polynomial time computation [5]. A second approach relies on the idea of tracking the size increase between input and output, and together with a restricted recursion scheme, to deduce time complexity bounds. This second approach is illustrated for instance by non-size-increasing types [8]. However, both approaches suffer from limitations. The first one, that of linear logic, has a limited intensional expressivity, that is to say some natural polynomial time programs are not typable. As to the second approach it is essentially linear, more precisely it does not allow for a non-linear use of functional arguments. In the present work we incorporate both approaches into a common type system, in order to overcome their respective constraints. The source language we consider is a lambda-calculus with data-types and iteration, that is to say a variant of Gödel's system T. Our goal is to design a system for this language allowing both to handle non-linear functional arguments and to keep a good intensional expressivity. We illustrate our methodology by choosing the system of elementary linear logic (ELL) and combining it with a system of linear size types. We discuss the expressivity of this new type system, called sEAL, and prove that it gives a characterization of the complexity classes FPTIME and 2k-FEXPTIME, for k ≥ 0. [ABSTRACT FROM AUTHOR]

Let A be an alphabet and S P ⋄ (A) denote the class of all countable N-free partially ordered sets labeled by A , in which chains are scattered linear orderings and antichains are finite. We characterize the rational languages of S P ⋄ (A) by means of logic. We define an extension of monadic second-order logic by Presburger arithmetic, named P-MSO, such that a language L of S P ⋄ (A) is rational if and only if L is the language of a sentence of P-MSO, with effective constructions from one formalism to the other. As a corollary, the P-MSO theory of S P ⋄ (A) is decidable. [ABSTRACT FROM AUTHOR]

This paper introduces Graded Computation Tree Logic with finite path semantics (GCTL f ⁎ , for short), a variant of Computation Tree Logic CTL⁎, in which path quantifiers are interpreted over finite paths and can count the number of such paths. State formulas of GCTL f ⁎ are interpreted over Kripke structures. The syntax of GCTL f ⁎ has path quantifiers of the form E ≥ g ψ which express that there are at least g many distinct finite paths that satisfy ψ. After defining and justifying the logic GCTL f ⁎ , we solve its model checking problem and establish that its computational complexity is PSPACE-complete. Moreover, we investigate GCTL f ⁎ under the imperfect information setting. Precisely, we introduce GCTLK f ⁎ , an epistemic extension of GCTL f ⁎ and prove that the model checking problem also in this case is PSPACE-complete. [ABSTRACT FROM AUTHOR]

We consider the one-variable fragment of first-order logic extended with Presburger constraints. The logic is designed in such a way that it subsumes the previously-known fragments extended with counting, modulo counting or cardinality comparison and combines their expressive powers. We prove Image 1 -completeness of the logic by presenting an optimal algorithm for solving its finite satisfiability problem. [ABSTRACT FROM AUTHOR]

Halpern and Shoham modal logic of time intervals (HS in short) is an elegant and highly influential propositional interval-based modal logic. Its sub-propositional fragments, that is fragments obtained by restricting use of propositional connectives, and their hybrid extensions with nominals and satisfaction operators have been recently studied and successfully applied in real-world use cases. Detailed investigation of their decidability and computational complexity has been conducted, however, there has been significantly less research on their expressive power. In this paper we make a step towards filling this gap. In particular, we (1) compare classes of frames definable in full HS and in its hybrid extension, and (2) determine in which sub-propositional HS -fragments we can express the difference operator, nominals, and satisfaction operators. The obtained results enable us to classify HS , its sub-propositional fragments, and their hybrid extensions according to their expressive power. [ABSTRACT FROM AUTHOR]

We study a variant ATL FB of the alternating-time temporal logic ATL with a non-standard, 'finitely bounded' semantics (FBS). FBS was originally defined as a game-theoretic semantics where players must commit to time limits when attempting to verify eventuality (respectively, to falsify safety) formulae. It turns out that FBS has a natural corresponding compositional semantics that essentially evaluates formulae only on finite initial segments of paths and imposes uniform bounds on all plays for the fulfilment of eventualities. The resulting version ATL FB differs in some essential features from the standard ATL, as it no longer has the finite model property, though the two logics are equivalent on finite models. We develop two tableau systems for ATL FB. The first one deals with infinite sets of formulae and may run in a transfinite sequence of steps, whereas the second one deals only with finite sets of formulae in an extended language allowing explicit symbolic indication of time limits in formulae. We prove soundness and completeness of the infinitary tableau system and prove that it is equivalent to the finitary one. We also show that the finitary tableau system provides an exponential-time decision procedure for the satisfiability problem of ATL FB and thus establishes its EXPTIME-completeness. Furthermore, we present an infinitary axiomatization for ATL FB and prove its soundness and completeness. [ABSTRACT FROM AUTHOR]

In Temporal Logic (TL), a well-formed formula is generally formed by applying rules of its syntax finitely many times. However, under some circumstances, although formulas such as ones expressed by index set expressions , are constructed via applying rules of the syntax infinitely many times, they are possibly still well-formed since their equivalent concise syntax formulas can be found. With this motivation, this paper investigates the relationship between formulas specified by index set expressions and concise syntax by means of fixed-point approach. Firstly, we present two kinds of formulas, namely ⋁ i ∈ N 0 ◯ i Q and ⋁ i ∈ N 0 Q i , and prove they are indeed well-formed by proving they are equivalent to formulas ◇ Q and Q ⁎ respectively. Further, we generalize ⋁ i ∈ N 0 ◯ i Q to ⋁ i ∈ N 0 P (i) ∧ ◯ i Q and explore the least and greatest fixed-points of an abstract equation X ≡ Q ∨ P ∧ ◯ X. Based on these, some well-formed special instances of ⋁ i ∈ N 0 P (i) ∧ ◯ i Q are obtained. Besides, with the index set expression technique, we equivalently represent ' U ' (strong until) and ' W ' (weak until) constructs of propositional Linear Temporal Logic (LTL) within Propositional Projection Temporal Logic (PPTL). [ABSTRACT FROM AUTHOR]

When studying sequent calculi, proof theorists often have to prove properties about the systems, whether to show that they are "well-behaved", amenable to automated proof search, complete with respect to another system, consistent, among other reasons. These proofs usually involve many very similar cases, which leads to authors rarely writing them in full detail, only pointing to one or two more complicated cases. Moreover, the amount of details makes them more error-prone for humans. Computers, on the other hand, are very good at handling details and repetitiveness. In this work we have formalized textbook proofs of the meta-theory of sequent calculi for linear logic in Abella. Using the infrastructure developed, the proofs can be easily adapted to other substructural logics. We implemented rules as clauses in an intuitive and straightforward way, similar to logic programming, using operations on multisets for the explicit contexts. Although the proofs are quite big, they use only elementary reasoning principles, which makes the proof techniques fairly portable to other formal reasoning systems. [ABSTRACT FROM AUTHOR]

Among the very many research interests of Maurice Nivat, a special role, according to the produced literature, was played by the study of the algorithmic and combinatorial aspects of connected finite discrete sets of points called polyominoes. In particular, he addressed the problem of a faithful reconstruction of some subclasses of them by imposing convexity constraints. The present study fits in this research line, and relies on a well known algorithm that Maurice Nivat and co-authors defined 1996 for the reconstruction of hv -convex polyominoes by orthogonal projections in polynomial time. Here, we consider a hierarchy on this class of polyominoes, and we continue a longstanding research on the reconstruction of its first levels by specializing the above mentioned result. The algorithm we propose bases on the possibility of characterizing the elements of the second level of the hierarchy, by a logic formula belonging to Dual-Horn and so polynomially solvable. Some related open problems are also presented. [ABSTRACT FROM AUTHOR]

In this paper, we study the model checking problem of pushdown systems for projection temporal logic (PTL), an interval-based temporal logic that is as expressive as the full regular languages. For this, we provide an algorithm to decide whether a pushdown system, determined by a pushdown automaton, satisfies a desired logic property, by using relevant automata notations and operations. The algorithm terminates in exponential time for normal PTL properties, i.e. properties specified as normal PTL formulas. To show the lower bound of complexity of the model checking problem, we also construct a polynomial-time reduction from the acceptance problem of a linearly bounded alternating Turing machine. As a result, the model checking problem of pushdown systems for normal PTL properties is EXPTIME-complete. [ABSTRACT FROM AUTHOR]

To specify properties of open systems with interval based temporal logics, Alternating Projection Temporal Logic (APTL) is proposed by introducing Concurrent Game Structures (CGS) to Propositional Projection Temporal Logic (PPTL). Further, examples are given to show how properties of open systems can be specified by APTL formulas. Moreover, to establish the automata based model theory for the new proposed logic, Generalized alternating Büchi automata over Concurrent Game structures (GBCGs) are defined, and a transformation from APTL formulas to GBCGs is presented. In addition, a decision procedure for checking the satisfiability of APTL formulas, and a model checking approach for APTL with Concurrent Game Structures (CGSs) being models are presented. [ABSTRACT FROM AUTHOR]

Abstract Intensional computations are those that query the internal structure of their arguments. In a higher-order setting, such queries perform program analysis. This is beyond the expressive power of traditional term rewriting systems, such as lambda-calculus or combinatory logic, as they are extensional. In such settings it has been necessary to encode or quote the program before analysis. However, there are intensional calculi, specifically confluent term rewriting systems, that can analyse higher-order programs within the calculus proper, without quotation; there are even programs that produce the Goedel numbers of their program argument. This paper summarizes the current situation. Highlights include the following observations. We have known since 2011 that the simplest intensional calculus, SF-calculus, supports arbitrary queries of closed normal forms, including equality, pattern-matching, searching and self-interpretation. Recent work, verified using the Coq proof assistant, has shown that all recursive programs can be represented as closed normal forms in SF-calculus, and even in combinatory logic. Thus, we can here deduce that SF-calculus (but not combinatory logic) can define queries of programs. These results are compatible with direct support for lambda-abstraction. Although these results conflict with the traditional understanding of expressive power of combinatory logic and λ -calculus, as developed by Church and Kleene, our recent publication has shown that their approach is compromised by its reliance on encodings. To drive the point home, this paper uses a non-standard encoding to lambda-define a trivial solution of the Halting Problem. [ABSTRACT FROM AUTHOR]

An important problem when modelling gene networks lies in the identification of parameters, even when using a discrete framework such as the one of René Thomas. We present in this article a new approach based on Hoare logic to generate constraints on parameter values. Specifications of observed behaviours play a role comparable to programs in the classical Hoare logic, and deduced weakest preconditions characterize the sets of all compatible parameterizations, expressed as constraints on parameters. Besides being natural and simple, our Hoare logic approach is remarkably powerful and, among others, it allows one to express external interventions of the biologist during experiments such as knockouts. In supplementary materials, we give a proof of soundness of our Hoare logic for gene networks as well as a proof of completeness and decidability based on the notion of the weakest precondition. [ABSTRACT FROM AUTHOR]

We introduce a new concept in the area of formal logic: axioms for model morphisms. We work in the setting of specification languages that define the semantics of a theory as a category of models. While it is routine to use axioms to specify the class of models of a theory, there has so far been no analogue to systematically specify the morphisms between these models. This leads to subtle problems where it is difficult to give a theory that specifies the intended model category, or where seemingly isomorphic theories actually have non-isomorphic model categories. Our morphism axioms remedy this by providing new syntax for axiomatizing and reasoning about the properties of model morphisms. Additionally, our system resolves a subtle incompatibility between theory morphisms and model morphisms: the semantics that maps theories to model categories is functorial. While this result is standard in principle, previous formulations had to restrict the allowed theory morphisms or the allowed model morphisms. Our system allows establishing the result in full generality. [ABSTRACT FROM AUTHOR]

Algorithms for answering XPath queries on Xml streams have been studied intensively in the last decade. Nevertheless, there still exists no solution with high efficiency and large coverage. In this paper, we introduce early nested word automata in order to approximate earliest query answering algorithms for nested word automata. Our early query answering algorithm is based on stack-and-state sharing for running early nested word automata on all answer candidates with on-the-fly determinization. We prove tight upper complexity bounds on time and space consumption. We have implemented our algorithm in the QuiXPath system and show that it outperforms all previous tools in coverage on the XPathMark benchmark, while obtaining very high time and space efficiency and scaling to huge Xml streams. Furthermore, it turns out that our early query answering algorithm is earliest in practice on most queries from the XPathMark benchmark. 1 1 Thanks to the QuiXProc project of Inria and Innovimax and the Cnrs Sosp project. [ABSTRACT FROM AUTHOR]

Although there have been many works on bounded semantics, a characterization of a good definition for a bounded semantics has not been given, and this has led to definitions of bounded semantics of temporal logics that may not be appropriate with respect to the potential usefulness as a basis for developing bounded model checking approaches. On the other side, the research effort on bounded semantics has mainly focused on existentially interpreted fragments of temporal logics, due to the intricacy of defining appropriate bounded semantics for universally interpreted fragments, or for temporal logics with path quantifiers that are closed under negation. This work addresses these two problems, by defining the characteristics of bounded semantics for clarifying the concept of bounded semantics, and presenting a bounded semantics for the full set of CTL, a logic closed under negation, including possibility for specifying both existential and universal properties. [ABSTRACT FROM AUTHOR]

Dynamic graph theory is a novel, growing area that deals with graphs that change over time and is of great utility in modeling modern wireless, mobile and dynamic environments. As a graph evolves, possibly arbitrarily, it is challenging to identify the graph properties that can be preserved over time and understand their respective computability. In this paper we are concerned with the treewidth of dynamic graphs. We focus on metatheorems , which allow the generation of a series of results based on general properties of classes of structures. In graph theory two major metatheorems on treewidth provide complexity classifications by employing structural graph measures and finite model theory. Courcelle's Theorem gives a general tractability result for problems expressible in monadic second order logic on graphs of bounded treewidth, and Frick and Grohe demonstrate a similar result for first order logic and graphs of bounded local treewidth. We extend these theorems by showing that dynamic graphs of bounded (local) treewidth where the length of time over which the graph evolves and is observed is finite and bounded can be modeled in such a way that the (local) treewidth of the underlying graph is maintained. We show the application of these results to problems in dynamic graph theory and dynamic extensions to static problems. In addition we demonstrate that certain widely used dynamic graph classes have bounded local treewidth. [ABSTRACT FROM AUTHOR]

This paper presents a practical decision procedure for Propositional Projection Temporal Logic with infinite models. First, a set Prop l of labels l i , 0 ⩽ i ⩽ n ∈ N 0 , is used to mark nodes of an LNFG of a formula, and a node with l i is treated as an accepting state as in an automaton. Further, the generalized Büchi accepting condition for automata is employed to identify a path (resulting a word) in an LNFG as a model of the formula. In addition, the implementation details of the decision procedure and relevant algorithms including pre-processing, LNFG, circle finding algorithms are presented; as a matter of fact, all algorithms are implemented by C++ programs. [ABSTRACT FROM AUTHOR]

The problem of automated theorem finding is one of the 33 basic research problems in automated reasoning which was originally proposed by Wos in 1988, and it is still an open problem. To solve the problem, an approach of forward deduction based on the strong relevant logics was proposed. Following the approach, this paper presents a systematic methodology for automated theorem finding. To show the effectiveness of our methodology, the paper presents two case studies, one is automated theorem finding in NBG set theory and the other is automated theorem finding in Peano's arithmetic. Some known theorems have been found in our case studies. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper is to obtain a theoretical foundation of inconsistency-tolerant (or paraconsistent) reasoning by presenting a comprehensive study of the structural proof-theory of David Nelson’s paraconsistent logic. Inconsistency handling has a growing importance in Computer Science since inconsistencies may frequently occur in knowledge-based and intelligent information systems. Paraconsistent, inconsistency-tolerant logics have been studied to cope with such inconsistencies. In this paper, proof systems for Nelson’s paraconsistent logic N4 are comprehensively studied. The logic N4 is a fundamental system and known to be a common basis for various extended and useful paraconsistent logics. Some basic theorems including cut-elimination, normalization and completeness are uniformly proved using various embedding theorems. A variety of sequent calculi and natural deduction systems for N4 and some closely related systems are presented and compared. [Copyright &y& Elsevier]

Abstract: Inspired by the Multiplicative Exponential fragment of Linear Logic, we define a framework called the prismoid of resources where each vertex is a language which refines the -calculus by using a different choice to make explicit or implicit (meta-level) the definition of the contraction, weakening, and substitution operations. For all the calculi in the prismoid we show simulation of -reduction, confluence, preservation of -strong normalisation and strong normalisation for typed terms. Full composition also holds for all the calculi of the prismoid handling explicit substitutions. The whole development of the prismoid is done by making the set of resources a parameter of the formalism, so that all the properties for each vertex are obtained as a particular case of the general abstract proofs. [Copyright &y& Elsevier]

Abstract: A focused proof system provides a normal form to cut-free proofs in which the application of invertible and non-invertible inference rules is structured. Within linear logic, the focused proof system of Andreoli provides an elegant and comprehensive normal form for cut-free proofs. Within intuitionistic and classical logics, there are various different proof systems in the literature that exhibit focusing behavior. These focused proof systems have been applied to both the proof search and the proof normalization approaches to computation. We present a new, focused proof system for intuitionistic logic, called LJF, and show how other intuitionistic proof systems can be mapped into the new system by inserting logical connectives that prematurely stop focusing. We also use LJF to design a focused proof system LKF for classical logic. Our approach to the design and analysis of these systems is based on the completeness of focusing in linear logic and on the notion of polarity that appears in Girard’s LC and LU proof systems. [Copyright &y& Elsevier]

Abstract: In this paper, we consider the robust interpretation of Metric Temporal Logic (MTL) formulas over signals that take values in metric spaces. For such signals, which are generated by systems whose states are equipped with non-trivial metrics, for example continuous or hybrid, robustness is not only natural, but also a critical measure of system performance. Thus, we propose multi-valued semantics for MTL formulas, which capture not only the usual Boolean satisfiability of the formula, but also topological information regarding the distance, , from unsatisfiability. We prove that any other signal that remains -close to the initial one also satisfies the same MTL specification under the usual Boolean semantics. Finally, our framework is applied to the problem of testing formulas of two fragments of MTL, namely Metric Interval Temporal Logic (MITL) and closed Metric Temporal Logic (clMTL), over continuous-time signals using only discrete-time analysis. The motivating idea behind our approach is that if the continuous-time signal fulfills certain conditions and the discrete-time signal robustly satisfies the temporal logic specification, then the corresponding continuous-time signal should also satisfy the same temporal logic specification. [Copyright &y& Elsevier]

Abstract: Certain behavioral properties of distributed systems are difficult to express in interleaving semantics, whereas they are naturally expressed in terms of partial orders of events or, equivalently, Mazurkiewicz traces. Two examples of such properties are serializability of a database and global snapshots of concurrent systems. Recently, a modest extension for LTL by an operator that expresses snapshots, has been proposed. It combines the ease of linear (interleaving) specification with this useful partial order concept. The new construct allows one to assert that a global snapshot appeared in the past, perhaps not in the observed execution sequence, but possibly in an equivalent one. Originally, a model checking algorithm for this logic that is exponential space in the size of the system was suggested. In this paper, we provide a model checking algorithm that is in polynomial space in the size of the system. Our construction can also serve as an efficient (polynomial) algorithm for detecting conjunctive properties (i.e., conjunction of local process properties) in a concurrent history of execution. [Copyright &y& Elsevier]

Abstract: The calculus of Mobile Ambients has been introduced for expressing mobility and mobile computation. In this paper we present a probabilistic version of Mobile Ambients by augmenting the syntax of the original Ambient Calculus with a (guarded) probabilistic choice operator. To allow for the representation of both the probabilistic behaviour introduced through the new probabilistic choice operator and the nondeterminism present in the original Ambient Calculus we use probabilistic automata as the underpinning semantic model. The Ambient logic is a logic for Mobile Ambients that contains a novel treatment of both locations and hidden names. For specifying properties of Probabilistic Mobile Ambients, we extend this logic to specify probabilistic behaviour. In addition, to show the utility of our approach we present an example of a virus infecting a network. [Copyright &y& Elsevier]

Abstract: Commutative, integral and bounded -algebras form a subvariety of residuated lattices which provides the algebraic semantics of an interesting common fragment of intuitionistic logic and of several fuzzy logics. It is known that both the equational theory and the quasiequational theory of commutative -algebras are decidable (in contrast to the noncommutative case), but their complexity has not been studied yet. In this paper, we prove that both theories are in , and that the quasiequational theory is -hard. [Copyright &y& Elsevier]

Abstract: Eilenberg, Elgot and Shepherdson showed in 1969, [S. Eilenberg, C.C. Elgot, J.C. Shepherdson, Sets recognized by -tape automata, Journal of Algebra 13 (1969) 447–464], that a relation on finite words over a finite, non-unary alphabet with letters is definable in first order logic with predicates for the relations equal length, prefix and last letter is (for each letter ) if and only if it can be recognized by a finite multitape synchronous automaton, i.e., one whose read heads move simultaneously. They left open the characterization in the case of infinite alphabets, and proposed some conjectures concerning them. We solve all problems and sharpen the main theorem of [S. Eilenberg, C.C. Elgot, J.C. Shepherdson, Sets recognized by -tape automata, Journal of Algebra 13 (1969) 447–464]. [Copyright &y& Elsevier]

Abstract: This is a survey of results about versions of fine hierarchies and many-one reducibilities that appear in different parts of theoretical computer science. These notions and related techniques play a crucial role in understanding complexity of finite and infinite computations. We try not only to present the corresponding notions and facts from the particular fields but also to identify the unifying notions, techniques and ideas. [Copyright &y& Elsevier]

Abstract: We consider the notion of modular decomposition for countable graphs. The modular decomposition of a graph given with an enumeration of its set of vertices can be defined by formulas of monadic second-order logic. Another result is the definition of a representation of modular decompositions by low degree relational structures. Such relational structures can also be defined in the considered graph by monadic second-order formulas. [Copyright &y& Elsevier]

Abstract: We solve the Angel Problem, by describing a strategy that guarantees the win of an Angel of power 2 or greater. Basically, the Angel should move north as quickly as possible. However, he should detour around eaten squares, as long as the extra distance does not exceed twice the number of eaten squares evaded. We show that an Angel following this strategy will always spot a trap early enough to avoid it. [Copyright &y& Elsevier]

Abstract: We develop possible worlds (Kripke) semantics at the categorical abstract model theoretic level provided by the so-called ‘institutions’. Our general abstract modal logic framework provides a method for systematic Kripke semantics extensions of logical systems from computing science and logic. We also extend the institution-independent method of ultraproducts of [R. Diaconescu, Institution-independent ultraproducts, Fundamenta Informaticæ 55 (3–4) (2003) 321–348] to possible worlds semantics and prove a fundamental preservation result for abstract modal satisfaction. As a consequence we develop a generic compactness result for possible worlds semantics. [Copyright &y& Elsevier]

Abstract: We introduce a complexity measure of modal properties of finite structures which generalises the automaticity of languages. It is based on graph-automata-like devices called labelling systems. We define a measure of the size of a structure that we call rank, and show that any modal property of structures can be approximated up to any fixed rank by a labelling system. The function that takes to the size of the smallest labelling system doing this is called the labelling index of the property. We demonstrate that this is a useful and fine-grained measure of complexity and show that it is especially well suited to characterise the expressive power of modal fixed-point logics. From this we derive several separation results of modal and non-modal fixed-point logics, some of which are already known whereas others are new. [Copyright &y& Elsevier]

Abstract: The typical AI problem is that of making a plan of the actions to be performed by a robot so that the robot could get into a set of final situations, if it started with a certain initial situation. The planning problem is known to be generally very complex. Even within the case of ‘well-balanced’ actions, strong planning under uncertainty about the effects of actions, or games such as ‘Robot against Nature’, is EXPTIME-complete. As a result, AI planners are very sensitive to the number of the variables involved in making a plan, the inherent symmetry of the problem, and the nature of the logical formalisms being used. This paper shows that linear logic provides a convenient and adequate tool for representing strong and weak planning problems in non-deterministic domains. A particular focus of this paper is on planning problems with an unbounded number of functionally identical objects. We show that for such problems linear logic is especially effective and leads to a dramatic contraction of the search space from exponential to polynomial in size. We employ the ability of linear logic to reason about multisets, which in this instance are created by identifying several distinct objects as being functionally equivalent for the problem at hand (think of a number of balls, each of which must be moved to some new location — the balls are distinct, but are functionally equivalent for the problem). In linear logic terms, we establish a clear syntactic condition that allows us to show that solving a generic planning problem where there is only one generic object, directly implies a solution to the original real planning problem over several real objects, the isomorphic copies of the generic object. Moreover, this correspondence also guarantees to produce a real solution that works in polynomial time. [Copyright &y& Elsevier]

Abstract: We show that a class of vertex partitioning problems that can be expressed in monadic second order logic (MSOL) are polynomials on graphs of bounded clique-width. This class includes coloring, -free coloring, domatic number and partition into perfect graphs. Moreover we show that a class of vertex and edge partitioning problems are polynomials on graphs of bounded treewidth. [Copyright &y& Elsevier]

Abstract: For a propositional proof system we introduce the complexity class of all disjoint -pairs for which the disjointness of the pair is efficiently provable in the proof system . We exhibit structural properties of proof systems which make canonical -pairs associated with these proof systems hard or complete for . Moreover, we demonstrate that non-equivalent proof systems can have equivalent canonical pairs and that depending on the properties of the proof systems different scenarios for and the reductions between the canonical pairs exist. [Copyright &y& Elsevier]

Abstract: Context-aware computing refers to a paradigm in which applications sense aspects of the environment and use this information to adjust their behavior in response to changing circumstances. In this paper, we present a formal model and notation (Context UNITY) for expressing quintessential aspects of context-aware computations; existential quantification, for instance, proves to be highly effective in capturing the notion of discovery in open systems. Furthermore, Context UNITY treats context in a manner that is relative to the specific needs of an individual application and promotes an approach to context maintenance that is transparent to the application. In this paper, we construct the model from first principles, introduce its proof logic, and demonstrate how the model can be used as an effective abstraction tool for context-aware applications and middleware. [Copyright &y& Elsevier]

Abstract: In this paper we show how a resource-oriented logic, separation logic, can be used to reason about the usage of resources in concurrent programs. [Copyright &y& Elsevier]

Abstract: We present a trace semantics for a language of parallel programs which share access to mutable data. We introduce a resource-sensitive logic for partial correctness, based on a recent proposal of O’Hearn, adapting separation logic to the concurrent setting. The logic allows proofs of parallel programs in which “ownership” of critical data, such as the right to access, update or deallocate a pointer, is transferred dynamically between concurrent processes. We prove soundness of the logic, using a novel “local” interpretation of traces which allows accurate reasoning about ownership. We show that every provable program is race-free. [Copyright &y& Elsevier]

Abstract: In this paper, we introduce the split game, a variant of the Ehrenfeucht–Fraïssé game from logic, which is useful for analyzing the expressive power of classes of generalized regular expressions. An extension of the split game to generalized -regular expressions is also established. To gain insight into how the split game can be applied to attack the long-standing generalized star height 2 problem, we propose and solve the omega power problem, a similar but tractable problem in the context of -languages. Namely we show that omega powers, together with boolean combinations and concatenations, are not sufficient to express the class of -regular languages. [Copyright &y& Elsevier]