Three notes on the complexity of model checking fixpoint logic with chop

This paper analyses the complexity of model checking fixpoint logic with Chop – an extension of the modal μ-calculus with a sequential composition operator. It uses two known game-based characterisations to derive the following results: the combined model checking complexity as well as the data complexity of FLC are EXPTIME-complete. This is already the case for its alternation-free fragment. The expression complexity of FLC is trivially P-hard and limited from above by the complexity of solving a parity game, i.e. in UP ∩ co-UP. For any fragment of fixed alternation depth, in particular alternation- free formulas it is P-complete

European Social Models and Growth: Where are the Eastern European countries heading?

The authors find that as they seek to develop a social model both appropriate to their needs and consistent with EU standards, Eastern European countries must understand that a single European Social Model does not exist. Recently, some Eastern European unionists have begun to support their demands with reference to the European Social Model, which they only comprehend, however, in terms of its most inefficient Continental form. Eastern European countries must engage in a deeper public discussion of the pros and cons of various diverse social models, while taking into account the effects of different social models on the past and future competitiveness of the countries that have adopted them. Let those models compete to open opportunities based on forward-looking approach with full respect to the minimum harmonized standards (such as social safety net etc.) instead of fixing the past.European social model, competitiveness, welfare, public goods

Eventually Consistent Configuration Management in Fog Systems with CRDTs

Current fog systems rely on centralized and strongly consistent services for configuration management originally designed for cloud systems. In the geo-distributed fog, such systems can exhibit high communication latency or become unavailable in case of network partition. In this paper, we examine the drawbacks of strong consistency for fog configuration management and propose an alternative based on CRDTs. We prototypically implement our approach for the FReD fog data management platform. Early results show reductions of server response times of up to 50%

A template-based approach for the generation of abstractable and reducible models of featured networks

We investigate the relationship between symmetry reduction and inductive reasoning when applied to model checking networks of featured components. Popular reduction techniques for combatting state space explosion in model checking, like abstraction and symmetry reduction, can only be applied effectively when the natural symmetry of a system is not destroyed during specification. We introduce a property which ensures this is preserved, open symmetry. We describe a template-based approach for the construction of open symmetric Promela specifications of featured systems. For certain systems (safely featured parameterised systems) our generated specifications are suitable for conversion to abstract specifications representing any size of network. This enables feature interaction analysis to be carried out, via model checking and induction, for systems of any number of featured components. In addition, we show how, for any balanced network of components, by using a graphical representation of the features and the process communication structure, a group of permutations of the underlying state space of the generated specification can be determined easily. Due to the open symmetry of our Promela specifications, this group of permutations can be used directly for symmetry reduced model checking. The main contributions of this paper are an automatic method for developing open symmetric specifications which can be used for generic feature interaction analysis, and the novel application of symmetry detection and reduction in the context of model checking featured networks. We apply our techniques to a well known example of a featured network – an email system

One threat - multiple responses : countering hybrid threats in V4 countries

Nowa dynamika w globalnym środowisku bezpieczeństwa, której towarzyszył powrót do rywalizacji mocarstw i jej wpływ na zapewnienie bezpieczeństwa państw Europy Środkowej, przyniosła nowe wyzwania, zwłaszcza w zakresie przeciwdziałania zagrożeniom hybrydowym. Artykuł przedstawia wyniki badań analizujących strategie przeciwdziałania zagrożeniom hybrydowym w czterech krajach wyszehradzkich: w Czechach, na Węgrzech, w Polsce i na Słowacji. Celem artykułu jest omówienie i wyjaśnienie polityki tych czterech państw w odniesieniu do złożoności wyzwań hybrydowych oraz zdolności ich łagodzenia. Narodowe stanowiska zostały wszechstronnie ocenione w czterech studiach przypadków. Omówiono ich główne podobieństwa i kluczowe różnice. Wniosek z przeprowadzonych badań wskazuje na to, że chociaż kraje V4 mają te same podstawy koncepcyjno-teoretyczne, to polityki wobec zagrożenia hybrydowego są różne. Autorzy proponują sprawniejsze działanie na poziomie krajowym oraz poprawę koordynacji między krajami V4.The new dynamics in the global security environment accompanied by the renewal of great power competition and its impact on security provision of Central European countries brought new challenges, especially in countering hybrid threats. The article embraces the outcome of a multilateral research analysing countering hybrid threat policies in the four Visegrad countries: Czech Republic, Hungary, Poland, and Slovakia. The goal of the article is to discuss and explain the four nations' policies towards the mitigation of the hybrid challenges and their complexity. Those national approaches are comprehensively assessed in four case studies and their main commonalities and key differences are discussed. The conclusion is that although the V4 countries have the same conceptual theoretical basis, the policies against the hybrid threat differ. The authors propose more efficient way ahead at the national level and the improvement of coordination between the V4 countries

Bialgebraic Semantics for String Diagrams

Turi and Plotkin's bialgebraic semantics is an abstract approach to specifying the operational semantics of a system, by means of a distributive law between its syntax (encoded as a monad) and its dynamics (an endofunctor). This setup is instrumental in showing that a semantic specification (a coalgebra) satisfies desirable properties: in particular, that it is compositional. In this work, we use the bialgebraic approach to derive well-behaved structural operational semantics of string diagrams, a graphical syntax that is increasingly used in the study of interacting systems across different disciplines. Our analysis relies on representing the two-dimensional operations underlying string diagrams in various categories as a monad, and their bialgebraic semantics in terms of a distributive law over that monad. As a proof of concept, we provide bialgebraic compositional semantics for a versatile string diagrammatic language which has been used to model both signal flow graphs (control theory) and Petri nets (concurrency theory). Moreover, our approach reveals a correspondence between two different interpretations of the Frobenius equations on string diagrams and two synchronisation mechanisms for processes, \`a la Hoare and \`a la Milner.Comment: Accepted for publications in the proceedings of the 30th International Conference on Concurrency Theory (CONCUR 2019

A Survey on Continuous Time Computations

We provide an overview of theories of continuous time computation. These theories allow us to understand both the hardness of questions related to continuous time dynamical systems and the computational power of continuous time analog models. We survey the existing models, summarizing results, and point to relevant references in the literature

Parameterized verification

The goal of parameterized verification is to prove the correctness of a system specification regardless of the number of its components. The problem is of interest in several different areas: verification of hardware design, multithreaded programs, distributed systems, and communication protocols. The problem is undecidable in general. Solutions for restricted classes of systems and properties have been studied in areas like theorem proving, model checking, automata and logic, process algebra, and constraint solving. In this introduction to the special issue, dedicated to a selection of works from the Parameterized Verification workshop PV \u201914 and PV \u201915, we survey some of the works developed in this research area