Conference: Logic in Computer Science - LICS, 2013]]>

Conference: Logic in Computer Science - LICS, pp. 335-344, 2011]]>

Conference: Logic in Computer Science - LICS, pp. 301-310, 2011]]>

While much of the current study on quantum computation employs low-level formalisms such as quantum circuits, several high-level languages/calculi have been recently proposed aiming at structured quantum programming. The current work contributes to the semantical study of such languages, by providing interaction-based semantics of a func- tional quantum programming language; the latter is based on linear ...

Conference: Logic in Computer Science - LICS, pp. 237-246, 2011]]>In semantics and in programming practice, algebraic concepts such as monads or, essentially equivalently, (large) Lawvere theories are a well-established tool for modelling generic side-effects. An important issue in this context are combination mechanisms for such algebraic effects, which allow for the modular design of programming languages and verification logics. The most basic combination operators are sum and ...

Conference: Logic in Computer Science - LICS, vol. abs/1101.2, pp. 227-236, 2011]]>Conference: Logic in Computer Science - LICS, pp. 279-288, 2011]]>

Conference: Logic in Computer Science - LICS, vol. abs/1104.0, pp. 133-142, 2011]]>

There is recently a significant effort to add quantita- tive objectives to formal verification and synthesis. We introduce and investigate the extension of temporal logics with quantitative atomic assertions, aiming for a general and flexible framework for quantitative-oriented specifications. In the heart of quantitative objectives lies the accumulation of values along a computation. It is either the accumulated summation, ...

Conference: Logic in Computer Science - LICS, pp. 43-52, 2011]]>Using Jeˇ´ abek's framework for probabilistic rea- soning, we formalize the correctness of two fundamental RNC 2 algorithms for bipartite perfect matching within the theory VPV for polytime reasoning. The first algorithm is for testing if a bipartite graph has a perfect matching, and is based on the Schwartz-Zippel Lemma for polynomial identity testing applied to the Edmonds ...

Conference: Logic in Computer Science - LICS, vol. abs/1103.5, pp. 185-194, 2011]]>We present the topos S of trees as a model of guarded recursion. We study the internal dependently-typed higher-order logic of S and show that S models two modal operators, on predicates and types, which serve as guards in recursive definitions of terms, predicates, and types. In particular, we show how to solve recursive type equations involving dependent ...

Conference: Logic in Computer Science - LICS, pp. 55-64, 2011]]>We study the two-variable fragments D 2 and IF 2 of dependence logic and independence-friendly logic. We consider the satisfiability and finite satisfiability problems of these logics and show that for D 2 , both problems are NEXPTIME-complete, whereas for IF 2 , the problems are 0 1 and 0 1 -complete, respectively. We also show that D 2 ...

Conference: Logic in Computer Science - LICS, vol. abs/1104.3, pp. 289-298, 2011]]>Conference: Logic in Computer Science - LICS, pp. 65-74, 2011]]>

Conference: Logic in Computer Science - LICS, pp. 13-22, 2011]]>

Conference: Logic in Computer Science - LICS, pp. 87-96, 2011]]>

Conference: Logic in Computer Science - LICS, pp. 387-396, 2011]]>

A bicategory of very general nondeterministic con- current games and strategies is presented. The intention is to formalize distributed games in which both Player (or a team of players) and Opponent (or a team of opponents) can interact in highly distributed fashion, without, for instance, enforcing that their moves alternate. I. INTRODUCTION This paper characterizes nondeterministic concurrent strate- gies in ...

Conference: Logic in Computer Science - LICS, pp. 409-418, 2011]]>Conference: Logic in Computer Science - LICS, pp. 143-151, 2011]]>

Our motivating question is a Myhill-Nerode theorem for infinite alphabets. We consider several kinds of those: alpha- bets whose letters can be compared only for equality, but also ones with more structure, such as a total order or a partial order. We develop a framework for studying such alphabets, where the key role is played by the automorphism group ...

Conference: Logic in Computer Science - LICS, pp. 355-364, 2011]]>We study Markov decision processes (MDPs) with multiple limit-average (or mean-payoff) functions. We consider two different objectives, namely, expectation and satisfaction objectives. Given an MDP with kk reward functions, in the expectation objective the goal is to maximize the expected limit- average value, and in the satisfaction objective the goal is to maximize the probability of runs such ...

Conference: Logic in Computer Science - LICS, vol. abs/1104.3, pp. 33-42, 2011]]>Conference: Logic in Computer Science - LICS, pp. 345-354, 2011]]>

Conference: Logic in Computer Science - LICS, pp. 321-328, 2011]]>

Conference: Logic in Computer Science - LICS, pp. 247-256, 2011]]>

We consider timed Petri nets, i.e., unbounded Petri nets where each token carries a real-valued clock. Transition arcs are labeled with time intervals, which specify constraints on the ages of tokens. Our cost model assigns token storage costs per time unit to places, and firing costs to transitions. We study the cost to reach a given control-state. ...

Conference: Logic in Computer Science - LICS, vol. abs/1104.0, pp. 399-408, 2011]]>We study the computability of conditional proba- bility, a fundamental notion in probability theory and Bayesian statistics. In the elementary discrete setting, a ratio of proba- bilities defines conditional probability. In more general settings, conditional probability is defined axiomatically, and the search for more constructive definitions is the subject of a rich literature in probability theory and statistics. However, we ...

Conference: Logic in Computer Science - LICS, pp. 107-116, 2011]]>We describe a denotational model of higher-order functional reactive programming using ultrametric spaces and nonexpansive maps, which provide a natural Cartesian closed generalization of causal stream functions and guarded recursive definitions. We define a type theory corresponding to this semantics and show that it satisfies normalization. Finally, we show how to efficiently implement reactive programs written in this language ...

Conference: Logic in Computer Science - LICS, pp. 257-266, 2011]]>We present a new fully abstract and effectively pre- sentable denotational model for RefML, a paradigmatic higher- order programming language combining call-by-value evaluation and general references in the style of ML. Our model is built using game semantics. In contrast to the previous model by Abramsky, Honda and McCusker (3), it provides a faithful account of reference types, ...

Conference: Logic in Computer Science - LICS, pp. 75-84, 2011]]>The Halpern-Shoham logic is a modal logic of time intervals. Some effort has been put in last ten years to clas- sify fragments of this beautiful logic with respect to decidability of its satisfiability problem. We complete this classification by showing — what we believe is quite an unexpected result — that the logic of subintervals, the fragment of the Halpern-...

Conference: Logic in Computer Science - LICS, pp. 377-386, 2011]]>Conference: Logic in Computer Science - LICS, pp. 97-106, 2011]]>

Additive linear logic, the fragment of linear logic concerning linear implication between strictly additive formu- lae, coincides with sum-product logic, the internal language of categories with free finite products and coproducts. Deciding equality of its proof terms, as imposed by the categorical laws, is complicated by the presence of the units (the initial and terminal objects of the category) ...

Conference: Logic in Computer Science - LICS, pp. 207-216, 2011]]>There are standard logics DTC, TC, and LFP capturing the complexity classes L, NL, and P on ordered structures, respectively. In (4) we have shown that LFPinv ,t he "order-invariant least fixed-point logic LFP," captures P (on all finite structures) if and only if there is a listing of the P- subsets of the set TAUT of propositional ...

Conference: Logic in Computer Science - LICS, vol. 18, pp. 20-174, 2011]]>Conference: Logic in Computer Science - LICS, pp. 311-320, 2011]]>

We extend languages of dot-depth one to infinite words. As for finite words, this class of languages corresponds to BSigma1, the first level of the quantifier alternation hierarchy of first-order logic FO = FO[<,+1,min,max]. We give a decidable characterization of BSigma1[<,+1,min] over infinite words; here, the max-predicate is void. Our characterization ...

Conference: Logic in Computer Science - LICS, vol. abs/1101.4, pp. 23-32, 2011]]>Conference: Logic in Computer Science - LICS, pp. 175-184, 2011]]>

We investigate the problem of type isomorphisms in a programming language with higher-order references. We first recall the game-theoretic model of higher-order references by Abramsky, Honda and McCusker. Solving an open problem by Laurent, we show that two finitely branching arenas are isomorphic if and only if they are geometrically the same, up to renaming of moves (...

Conference: Logic in Computer Science - LICS, pp. 152-161, 2011]]>Conference: Logic in Computer Science - LICS, pp. 197-206, 2011]]>

Conference: Logic in Computer Science - LICS, pp. 3-3, 2011]]>

Conference: Logic in Computer Science - LICS, pp. 4-5, 2011]]>

Conference: Logic in Computer Science - LICS, pp. 119-119, 2011]]>

The model checking of higher-order recursion schemes (higher-order model checking for short) has been actively studied in the last decade, and has seen significant progress in both theory and practice. From a practical perspec- tive, higher-order model checking provides a foundation for software model checkers for functional programming languages such as ML and Haskell. This short article ...

Conference: Logic in Computer Science - LICS, pp. 219-224, 2011]]>This paper introduces a new static analysis method for controlling and certifying imperative program runtime. We propose a type system to reflect information flow and to explore the computational complexity properties of well-typed programs. We exhibit a relation between Implicit Computational Complexity approaches and research on language-based

Conference: Logic in Computer Science - LICS, pp. 123-132, 2011]]>Conference: Logic in Computer Science - LICS, pp. 9-10, 2011]]>

Conference: Logic in Computer Science - LICS, pp. 365-374, 2011]]>

Conference: Logic in Computer Science - LICS, pp. 331-331, 2011]]>

Automatic structures are finitely presented structures where the universe and all relations can be recognized by finite automata. It is known that the isomorphism problem for automatic structures is complete for $\Sigma^1_1$; the first existential level of the analytical hierarchy. Several new results on isomorphism problems for automatic structures are shown in this paper: (i) The isomorphism problem ...

Conference: Logic in Computer Science - LICS, vol. abs/1001.2, pp. 160-169, 2010]]>We define tree automata with global constraints (TAGC), generalizing the well-known class of tree automata with global equality and disequality constraints (14) (TAGED). TAGC can test for equality and disequality between sub- terms whose positions are defined by the states reached dur- ing a computation. In particular, TAGC can check that all the subterms reaching a given state are ...

Conference: Logic in Computer Science - LICS, pp. 263-272, 2010]]>This paper summarizes results on a recently introduced family of Datalog-based languages, called Datalog+/-, which is a new framework for tractable ontology querying, and for a variety of other applications. Datalog+/- extends plain Datalog by features such as existentially quantified rule heads and, at the same time, restricts the rule syntax so as to achieve decidability and tractability. In ...

Conference: Logic in Computer Science - LICS, pp. 228-242, 2010]]>Evaluating a boolean conjunctive query q over a guarded first-order theory T is equivalent to checking whether (T & not q) is unsatisfiable. This problem is relevant to the areas of database theory and description logic. Since q may not be guarded, well known results about the decidability, complexity, and finite-model property of the guarded fragment do not ...

Conference: Logic in Computer Science - LICS, pp. 1-10, 2010]]>We develop a compositional behavioural model that integrates a variation of probabilistic automata into a conservative extension of interactive Markov chains. The model is rich enough to embody the semantics of generalised stochastic Petri nets. We define strong and weak bisimulations and discuss their compositionality properties. Weak bisimulation is partly oblivious to the probabilistic branching structure, in order to reflect ...

Conference: Logic in Computer Science - LICS, pp. 342-351, 2010]]>Separation logic has proven an effective formalism for the analysis of memory-manipulating programs. We show that the purely propositional fragment of separation logic is undecidable. In fact, for any choice of concrete heap-like model of separation logic, validity in that model remains undecidable. Besides its intrinsic technical interest, this result also provides new insights into the nature of ...

Conference: Logic in Computer Science - LICS, pp. 130-139, 2010]]>We develop the theory of regular cost functions over finite trees: aquantitative extension to the notion of regular languages of trees: Cost functions map each input (tree) to a value in ω + 1, and are considered modulo an equivalence relation which forgets about specific values, but preserves boundedness of functions on all subsets of the domain. We introduce nondeterministic ...

Conference: Logic in Computer Science - LICS, pp. 70-79, 2010]]>We solve the open problem of the decidability of Boolean BI logic (BBI), which can be considered as the core of separation and spatial logics. For this, we define a complete phase semantics for BBI and characterize it as trivial phase semantics. We deduce an embedding between trivial phase semantics for intuitionistic linear logic (ILL) and Kripke semantics for BBI. ...

Conference: Logic in Computer Science - LICS, pp. 140-149, 2010]]>We prove that fixed-point logic with counting captures polynomial time on all classes of graphs with excluded minors. That is, for every class C of graphs such that some graph H is not a minor of any graph in C, a property P of graphs in C is decidable in polynomial time if and only if it is definable ...

Conference: Logic in Computer Science - LICS, pp. 179-188, 2010]]>We propose a formal theory for contract-based computing. A contract is an agreement stipulated between two or more parties, which specifies the duties and the rights of the parties involved therein. We model contracts as formulae in an intuitionistic logic extended with a "contractual" form of implication. Decidability holds for our logic: this allows us to mechan- ically infer ...

Conference: Logic in Computer Science - LICS, pp. 332-341, 2010]]>Let R be a class of generators of node-labelled infinite trees, and Lbe a logical language for describing correctness properties of the setrees. Given r in R and phi in L, we say that r_phi is aphi-reflection of r just if (i) r and r_phi generate the same underlying tree, and (ii) suppose a node u ...

Conference: Logic in Computer Science - LICS, pp. 120-129, 2010]]>Stream circuits are a convenient graphical way to represent streams (or stream functions) computed by finite dimensional linear systems. We present a sound and complete expression calculus that allows us to reason about the semantic equivalence of finite closed stream circuits. For our proof of the soundness and completeness we build on recent ideas of Bonsangue, Rutten and Silva. They ...

Conference: Logic in Computer Science - LICS, pp. 421-430, 2010]]>Alternating timed automata are a powerful extension of classical Alur-Dill timed automata that are closed under all Boolean operations. They have played a key role, among others, in providing verification algorithms for prominent specification formalisms such as Metric Temporal Logic. Unfortunately, when interpreted over an infinite dense time domain (such as the reals), alternating time automata have an undecidable ...

Conference: Logic in Computer Science - LICS, pp. 60-69, 2010]]>A synchronization is a mechanism allowing two or more processes to perform actions at the same time. We study the expressive power of synchronizations gathering more and more processes simultaneously. We demonstrate the non- existence of a uniform, fully distributed translation of Mil- ner's CCS with synchronizations of n + 1 processes into CCS with synchronizations of n processes ...

Conference: Logic in Computer Science - LICS, pp. 382-391, 2010]]>Psi-calculi extend the pi-calculus with nominal datatypes to represent data, communication channels, and logics for facts and conditions. This general framework admits highly expressive formalisms such as concurrent higher-order constraints and advanced cryptographic primitives. We here establish the theory of weak bisimula- tion, where the actions are unobservable. In comparison to other calculi the presence of assertions ...

Conference: Logic in Computer Science - LICS, pp. 322-331, 2010]]>We construct finite groups whose Cayley graphs have large girth even w.r.t. a discounted distance measure that contracts arbitrarily long sequences of edges from the same colour class, and only counts transitions between colour classes. These groups are shown to be useful in the construction of finite bisimilar hypergraph covers that avoid any small cyclic configurations. We present ...

Conference: Logic in Computer Science - LICS, pp. 11-20, 2010]]>Parikh's Theorem states that semilinear sets are effectively equivalent with the Parikh images of regular languages and those of context-free languages. In this paper, we study the complexity of Parikh's Theorem over any fixed alphabet size d. We prove various normal form the oremsin the case of NFAs and CFGs. In particular, the normalform theorems ensure that ...

Conference: Logic in Computer Science - LICS, pp. 80-89, 2010]]>A fully abstract game semantics for an idealized programming language with local state and higher rank polymorphism - System F extended with general references - is described. It quite concrete, and extends existing games models by a simple development of the existing question/answer labelling to represent "copycat links" between positive and negative occurrences of type variables, using a notion of scoping ...

Conference: Logic in Computer Science - LICS, pp. 41-49, 2010]]>We consider formulas which, in addition to the symbols in the vocabulary, may use two designated symbolsand+ that must be interpreted as a linear order and its associated addition. Such a formula is called addition-invariant if, f or each fixed interpretation of the initial vocabulary, its result is independent of the particular interpretation ofand +. This paper studies the ...

Conference: Logic in Computer Science - LICS, pp. 273-282, 2010]]>Rule-based approaches (as in our own Kappa, or the BNG language, or many other propositions allowing the consideration of "reaction classes'') offer new and more powerful ways to capture the combinatorial interactions that are typical of molecular biological systems. They afford relatively compact and faithful descriptions of cellular interaction networks despite the combination of two broad types of interaction: ...

Conference: Logic in Computer Science - LICS, pp. 362-381, 2010]]>We design an intuitionistic predicate logic that supports a limited amount of classical reasoning, just enough to prove a variant of Markov's principle suited for predicate logic. At the computational level, the extraction of an existential witness out of a proof of its double negation is done by using a form of statically-bound exception mechanism, what can be ...

Conference: Logic in Computer Science - LICS, pp. 50-56, 2010]]>Polarized logic is the logic of values and continuations, and their interaction through continuation-passing style. The main limitations of this logic are the limitations of CPS: that continuations cannot be composed, and that programs are fully sequentialized. Delimited control operators were invented in response to the limitations of classical continuation-passing. That suggests the question: what is the logic ...

Conference: Logic in Computer Science - LICS, pp. 219-227, 2010]]>We define a new kind of automata recognizing properties of data words or data trees and prove that the automata capture all queries definable in Regular XPath. We show that the automata-theoretic approach may be applied to answer decidability and expressibility questions for XPath. Finally, we use the newly introduced automata as a common framework to classify existing automata ...

Conference: Logic in Computer Science - LICS, pp. 243-252, 2010]]>In our paper "Uniformity and the Taylor expansion of ordinary lambda-terms" (with Laurent Regnier), we studied a translation of lambda-terms as infinite linear combinatio ns of resource lambda-terms, from a calculus similar to Boudol's lambda-calculus with resources and based on ideas coming from differential linear logic and differential lambda-calculus. The good properties of this ...

Conference: Logic in Computer Science - LICS, vol. abs/1001.3, pp. 402-410, 2010]]>In recent years, there has been a growing interest in considering the probabilistic aspects of Information Flow. In this abstract we review some of the main approaches that have been considered to quantify the notion of information leakage, and we focus on some recent developments.

Conference: Logic in Computer Science - LICS, pp. 314-321, 2010]]>There are two usual ways to describe equality in a dependent typing system, one that uses an external notion of computation like beta-reduction, and one that introduces a typed judgement of beta-equality directly in the typing system. After being an open problem for some time, the general equivalence between both approaches has been solved by Adams for a ...

Conference: Logic in Computer Science - LICS, pp. 21-30, 2010]]>Conference: Logic in Computer Science - LICS, pp. 253-262, 2010]]>

We present a point of view concerning HOAS(Higher-Order Abstract Syntax) and an extensive exercise in HOAS along this point of view. The point of view is that HOAS can be soundly and fruitfully regarded as a definitional extension on top of FOAS (First-Order Abstract Syntax). As such, HOAS is not only an encoding technique, but also a ...

Conference: Logic in Computer Science - LICS, pp. 31-40, 2010]]>The paper discusses about the programming language ML (or MetaLanguage) as a language for manipulating formal systems. It has also had much influence on the further development of functional programming languages.

Conference: Logic in Computer Science - LICS, pp. 58-59, 2010]]>The following topics are dealt with: finite model theory; logic and automata; semantics; process calculi; and coalgebras.

Conference: Logic in Computer Science - LICS, pp. 57-57, 2010]]>This paper establishes a bridge between presheaf models for concurrency and the more operationally-informative world of event structures. It concentrates on a particular presheaf category, consisting of presheaves over finite partial orders of events; such presheaves form a model of nondeter- ministic processes in which the computation paths have the shape of partial orders. It is shown how with ...

Conference: Logic in Computer Science - LICS, pp. 392-401, 2010]]>This work belongs to a wider effort aimed at eliminating syntactic bureaucracy from proof systems. In this paper, we present a novel cut elimination procedure for classical propositional logic. It is based on the recently introduced atomic flows: they are purely graphical devices that ab- stract away from much of the typical bureaucracy of proofs. We make crucial use of ...

Conference: Logic in Computer Science - LICS, pp. 284-293, 2010]]>Summary form only given. Simple views of systems are often convenient in their design and analysis. However, attackers may attempt to exploit any oversimplification. For security, it is therefore useful to understand the value and the limitations of simplistic models. Computational-soundness theorems, which are the main subject of this lecture, can sometimes shed light on this question. We discuss ...

Conference: Logic in Computer Science - LICS, pp. 110-110, 2010]]>Maximality is a desirable property of paraconsistent logics, motivated by the aspiration to tolerate inconsistencies, but at the same time retain as much as possible from classical logic. In this paper we introduce a new, strong notion of maximal paraconsistency, which is based on possible extensions of the consequence relation of a logic. We investigate this notion in the framework ...

Conference: Logic in Computer Science - LICS, pp. 304-313, 2010]]>Fixed point combinators (and their generalization: looping combinators) are classic notions belonging to the heart of λ-calculus and logic. We start with an exploration of the structure of fixed point combinators (fpc's), vastly generalizing the wellknown fact that if Yis an fpc, Y(SI) is again an fpc, generating the Böhm sequence of fpc's. Using the infinitary ...

Conference: Logic in Computer Science - LICS, pp. 111-119, 2010]]>We provide a syntactic analysis of contextual preorder and equivalence for a polymorphic programming language with effects. Our approach applies uniformly across a range of {algebraic effects}, and incorporates, as instances: errors, input/output, global state, nondeterminism, probabilistic choice, and combinations thereof. Our approach is to extend Plotkin and Power's structural operational semantics for algebraic effects (FoSSaCS 2001) with ...

Conference: Logic in Computer Science - LICS, pp. 209-218, 2010]]>Traditional Gödel completeness holds between finite proofs and infinite models over formulas of finite depth, where proofs and models are heterogeneous. Our purpose is to provide an interactive form of completeness between infinite proofs and infinite models over formulas of infinite depth (that include recursive types), where proofs and models are homogenous. We work on a nonlinear extension of ludics, ...

Conference: Logic in Computer Science - LICS, pp. 294-303, 2010]]>Summary form only given. Since Turing, computer scientists have understood that the question "does this program satisfy its specifications?" could be reduced to the question "are these formulas theorems?" But the theorem proving technology of the 50s and 60s was inadequate for the task. In 1971, here in Edinburgh, Boyer and I started building the first general-purpose theorem prover ...

Conference: Logic in Computer Science - LICS, pp. 283-283, 2010]]>We provide two new characterizations for finitely generated varieties with Taylor terms. The first characterization is using "absorbing sets" and the second one "cyclic operations". These new conditions allow us to reprove the conjecture of Bang-Jensen and Hell (proved by the authors, comp. STOC'08, SICOMP'09) and the characterization of locally finite Taylor varieties using weak near-unanimity ...

Conference: Logic in Computer Science - LICS, pp. 100-109, 2010]]>Courcelle's famous theorem from 1990 states that any property of graphs definable in monadic second-order logic with quantification over edge sets (MSO) can be decided in linear time on any class of graphs of bounded tree-width, or in other words, MSO is fixed-parameter tractable on any such class of graphs. From a logical perspective, Courcelle's ...

Conference: Logic in Computer Science - LICS, vol. abs/1001.5, pp. 189-198, 2010]]>Every finitary monad T on the category of sets is described by an algebraic theory whose n-ary operations are the elements of the free algebra Tn generated by n letters. This canonical presentation of the monad (called its Lawvere theory) offers a precious guideline in the search for an intuitive presentation of the monad by generators and relations. Hence, ...

Conference: Logic in Computer Science - LICS, pp. 150-159, 2010]]>Is there any cartesian-closed category of continuous domains that would be closed under Jones and Plotkin's probabilistic powerdomain construction? This is a major open problem in the area of denotational semantics of probabilistic higher-order languages. We relax the question, and look for quasi-continuous dcpos instead. These retain many nice properties from continuous dcpos. We introduce a ...

Conference: Logic in Computer Science - LICS, pp. 352-361, 2010]]>One of the major interests of finite model theory is to separate the expressive power of different logics or fragments of logics. In this paper, we define a variant of Ehrenfeucht-Fraïssé games that characterizes quantifier classes over finite structures and prove that the fragments of first-order logic based on quantifier structures form a strict hierarchy in terms of ...

Conference: Logic in Computer Science - LICS, pp. 170-178, 2010]]>We prove that it is decidable whether a regular unranked tree language is definable in FO2(<;h,<;v). By FO2(<;h,<;v) we refer to the two variable fragment of first order logic built from the descendant and following sibling predicates. In terms of expressive power it corresponds to a fragment of the navigational core of ...

Conference: Logic in Computer Science - LICS, pp. 253-262, 2010]]>Conference: Logic in Computer Science - LICS, 2010]]>

We consider the standard model of finite two-person zero-sum stochastic games with signals. We are interested in the existence of almost-surely winning or positively win- ning strategies, under reachability, safety, B¨ uchi or co- B¨ uchi winning objectives. We prove two qualitative deter- minacy results. First, in a reachability game either player 1 can achieve almost-surely ...

Conference: Logic in Computer Science - LICS, pp. 319-328, 2009]]>We show how to reason about "step-indexed" logi- cal relations in an abstract way, avoiding the tedious, error-prone, and proof-obscuring step-index arithmetic that seems superficially to be an essential element of the method. Specifically, we define a logic LSLR, which is inspired by Plotkin and Abadi's logic for parametricity, but also sup- ports recursively defined ...

Conference: Logic in Computer Science - LICS, pp. 71-80, 2009]]>The model checking of higher-order recursion schemes has important applications in the verification of higher- order programs. Ong has previously shown that the modal mu-calculus model checking of trees generated by order- n recursion scheme is n-EXPTIME complete, but his algo- rithm and its correctness proof were rather complex. We give an alternative, type-based verification method: ...

Conference: Logic in Computer Science - LICS, pp. 179-188, 2009]]>We show that the syntactically rich notion of inductive families can be reduced to a core type theory with a fixed number of type constructors exploiting the novel notion of indexed containers. Indexed containers generalize simple containers, capturing strictly positive families instead of just strictly positive types, without having to extend the core type theory. Other applications of indexed containers ...

Conference: Logic in Computer Science - LICS, pp. 277-285, 2009]]>The reachability problem for Vector Addition Systems (VASs) is a central problem of net theory. The general problem is known decidable by algorithms exclusively based on the classical Kosaraju-Lambert-Mayr-Sacerdote- Tenney decomposition. This decomposition is used in this paper to prove that the Parikh images of languages accepted by VASs are semi-pseudo-linear; a class that extends ...

Conference: Logic in Computer Science - LICS, vol. abs/1009.1, pp. 4-13, 2009]]>We study the following problem: given a continuous- time Markov chain (CTMC) C, and a linear real-time property provided as a deterministic timed automaton (DTA) A, what is the probability of the set of paths of C that are accepted by A (C satisfies A)? It is shown that this set of paths is measurable and computing its probability ...

Conference: Logic in Computer Science - LICS, pp. 309-318, 2009]]>This paper presents a new lower bound for the discrete strategy improvement algorithm for solving parity games due to V¨ oge and Jurdzi´ nski. First, we informally show which structures are difficult to solve for the algorithm. Sec- ond, we outline a family of games on which the algorithm requires exponentially many strategy iterations, answering in the negative the long-...

Conference: Logic in Computer Science - LICS, pp. 145-156, 2009]]>Abstract—One-counter processes are pushdown,systems over a,singleton,stack,alphabet,(plus a,stack-bottom,symbol). We study,the complexity,of two,closely related verification problems,over,one-counter,processes: model,checking,with the temporal logic EF, where formulas are given as directed acyclic graphs, and weak bisimilarity checking against finite systems. We show,that both problems,are P,[...

Conference: Logic in Computer Science - LICS, pp. 235-244, 2009]]>We prove that is possible to extend Girard's Ludics so as to have repetitions (hence exponentials), and still have the results on semantical types which characterize Ludics in the panorama of Game Semantics. The results are obtained by using less structure than in the original paper; this has an interest on its own, and we hope that it will ...

Conference: Logic in Computer Science - LICS, pp. 375-384, 2009]]>We study the complexity of evaluating positive equality-free sentences of rst-order (FO) logic over a xed, nite structure B. This may be seen as a natural generalisation of the non- uniform quantied constraint satisfaction problem QCSP(B). We introduce surjective hyper- endomorphisms and use them in proving a Galois connection that characterises denability in positive equality-free FO. ...

Conference: Logic in Computer Science - LICS, vol. abs/1003.0, pp. 429-438, 2009]]>In the work of Nash et al. (2005) have raised the question whether a logic Lles, already introduced by Gurevich in 1988, captures polynomial time, and they give a reformulation of this question in terms of a parameterized halting problem p-Accles for nondeterministic Turing machines. We analyze the precise relationship between Lles and p-Accles. We show that p-...

Conference: Logic in Computer Science - LICS, pp. 397-406, 2009]]>The problem of Pairwise CFL-reachability is to decide whether two given program locations in different threads are simultaneously reachable in the presence of recursion in threads and scheduling constraints imposed by synchro- nization primitives. Pairwise CFL-reachability is the cor e problem underlying concurrent program analysis especiall y dataflow analysis. Unfortunately, it is undecidable even fo r the most ...

Conference: Logic in Computer Science - LICS, pp. 27-36, 2009]]>