Showing papers in "Acta Informatica in 2017"

A theory of formal synthesis via inductive learning

Abstract: Formal synthesis is the process of generating a program satisfying a high-level formal specification. In recent times, effective formal synthesis methods have been proposed based on the use of inductive learning. We refer to this class of methods that learn programs from examples as formal inductive synthesis. In this paper, we present a theoretical framework for formal inductive synthesis. We discuss how formal inductive synthesis differs from traditional machine learning. We then describe oracle-guided inductive synthesis (OGIS), a framework that captures a family of synthesizers that operate by iteratively querying an oracle. An instance of OGIS that has had much practical impact is counterexample-guided inductive synthesis (CEGIS). We present a theoretical characterization of CEGIS for learning any program that computes a recursive language. In particular, we analyze the relative power of CEGIS variants where the types of counterexamples generated by the oracle varies. We also consider the impact of bounded versus unbounded memory available to the learning algorithm. In the special case where the universe of candidate programs is finite, we relate the speed of convergence to the notion of teaching dimension studied in machine learning theory. Altogether, the results of the paper take a first step towards a theoretical foundation for the emerging field of formal inductive synthesis.

The Teacher Wars: A History of America’s Most Embattled Profession

Abstract: Dana Goldstein je novinarka i spisateljica te dobitnica nekoliko cijenjenih stipendija na području novinarstva. Piše o obrazovanju, ženskim pitanjima, nejednakosti i kaznenom pravosuđu. Njena knjiga „The Teacher Wars“ u kojoj pokriva 175 godina povijesti američkog školstva postala je bestseler New York Timesa što je učinilo Goldstein jednom od najcjenjenijih mladih novinarki u Sjedinjenim Američkim Državama.

Precise parameter synthesis for stochastic biochemical systems

Abstract: We consider the problem of synthesising rate parameters for stochastic biochemical networks so that a given time-bounded CSL property is guaranteed to hold, or, in the case of quantitative properties, the probability of satisfying the property is maximised or minimised. Our method is based on extending CSL model checking and standard uniformisation to parametric models, in order to compute safe bounds on the satisfaction probability of the property. We develop synthesis algorithms that yield answers that are precise to within an arbitrarily small tolerance value. The algorithms combine the computation of probability bounds with the refinement and sampling of the parameter space. Our methods are precise and efficient, and improve on existing approximate techniques that employ discretisation and refinement. We evaluate the usefulness of the methods by synthesising rates for three biologically motivated case studies: infection control for a SIR epidemic model; reliability analysis of molecular computation by a DNA walker; and bistability in the gene regulation of the mammalian cell cycle.

Stateless model checking for TSO and PSO

Abstract: We present a technique for efficient stateless model checking of programs that execute under the relaxed memory models TSO and PSO. The basis for our technique is a novel representation of executions under TSO and PSO, called chronological traces. Chronological traces induce a partial order relation on relaxed memory executions, capturing dependencies that are needed to represent the interaction via shared variables. They are optimal in the sense that they only distinguish computations that are inequivalent under the widely-used representation by Shasha and Snir. This allows an optimal dynamic partial order reduction algorithm to explore a minimal number of executions while still guaranteeing full coverage. We apply our techniques to check, under the TSO and PSO memory models, LLVM assembly produced for C/pthreads programs. Our experiments show that our technique reduces the verification effort for relaxed memory models to be almost that for the standard model of sequential consistency. This article is an extended version of Abdulla et al. (Tools and algorithms for the construction and analysis of systems, Springer, New York, pp 353–367, 2015), appearing in TACAS 2015.

Verification of population protocols

Abstract: Population protocols (Angluin et al. in PODC, 2004) are a formal model of sensor networks consisting of identical mobile devices. Two devices can interact and thereby change their states. Computations are infinite sequences of interactions satisfying a strong fairness constraint. A population protocol is well specified if for every initial configuration C of devices, and every computation starting at C, all devices eventually agree on a consensus value depending only on C. If a protocol is well specified, then it is said to compute the predicate that assigns to each initial configuration its consensus value. While the computational power of well-specified protocols has been extensively studied, the two basic verification problems remain open: Is a given protocol well specified? Does a given protocol compute a given predicate? We prove that both problems are decidable by reduction to the reachability problem of Petri nets. We also give a new proof of the fact that the predicates computed by well-defined protocols are those definable in Presburger arithmetic (Angluin et al. in PODC, 2006).

Assume-admissible synthesis

Abstract: In this paper, we introduce a novel rule for synthesis of reactive systems, applicable to systems made of n components which have each their own objectives. This rule is based on the notion of admissible strategies. We compare this rule with previous rules defined in the literature, and show that contrary to the previous proposals, it defines sets of solutions which are rectangular. This property leads to solutions which are robust and resilient, and allows one to synthesize strategies separately for each agent. We provide algorithms with optimal complexity and also an abstraction framework compatible with the new rule.

Multiparty session types as coherence proofs

Abstract: We propose a Curry---Howard correspondence between a language for programming multiparty sessions and a generalisation of Classical Linear Logic (CLL). In this framework, propositions correspond to the local behaviour of a participant in a multiparty session type, proofs to processes, and proof normalisation to executing communications. Our key contribution is generalising duality, from CLL, to a new notion of n-ary compatibility, called coherence. Building on coherence as a principle of compositionality, we generalise the cut rule of CLL to a new rule for composing many processes communicating in a multiparty session. We prove the soundness of our model by showing the admissibility of our new rule, which entails deadlock-freedom via our correspondence.

Efficient and secure attribute-based signature for monotone predicates

Abstract: Attribute-based signature (ABS) is a novel cryptographic primitive, which can make the signing party sign a message with fine-grained control over identifying information ABS only reveals the fact that the verified message must be signed by a user with a set of attributes satisfying a predicate Thus, ABS can hide any identifying information and make fine-grained control on signing Presently, many attribute-based signature schemes have been proposed, but most of them are not very efficient Maji et al recently presented a complete definition and construction about ABS for monotone predicates and showed three instantiations under their framework for ABS Although the most practical one of their instantiations is efficient, the instantiation is constructed in the generic group model and has been proved to be insecure Then, Okamoto et al proposed an attribute-based signature scheme in the standard model, which can support generalized non-monotone predicates over access structure However, their scheme is not efficient in practice In this paper, we present a framework for ABS and show a detailed security model for ABS Under our framework, we present an attribute-based signature scheme for monotone predicates in the standard model, where we choose the Waters' signature scheme as the prototype of our attribute-based signature scheme Compared with the Maji's scheme in the generic group model, the proposed scheme is constructed in the standard model Furthermore, compared with the Okamoto's scheme, the proposed scheme is more efficient by decreasing the computation cost

A general account of coinduction up-to

Abstract: Bisimulation up-to enhances the coinductive proof method for bisimilarity, providing efficient proof techniques for checking properties of different kinds of systems. We prove the soundness of such techniques in a fibrational setting, building on the seminal work of Hermida and Jacobs. This allows us to systematically obtain up-to techniques not only for bisimilarity but for a large class of coinductive predicates modeled as coalgebras. The fact that bisimulations up to context can be safely used in any language specified by GSOS rules can also be seen as an instance of our framework, using the well-known observation by Turi and Plotkin that such languages form bialgebras. In the second part of the paper, we provide a new categorical treatment of weak bisimilarity on labeled transition systems and we prove the soundness of up-to context for weak bisimulations of systems specified by cool rule formats, as defined by Bloom to ensure congruence of weak bisimilarity. The weak transition systems obtained from such cool rules give rise to lax bialgebras, rather than to bialgebras. Hence, to reach our goal, we extend the categorical framework developed in the first part to an ordered setting.

Dynamic Bayesian networks for formal verification of structured stochastic processes

Abstract: We study the problem of finite-horizon probabilistic invariance for discrete-time Markov processes over general (uncountable) state spaces. We compute discrete-time, finite-state Markov chains as formal abstractions of the given Markov processes. Our abstraction differs from existing approaches in two ways: first, we exploit the structure of the underlying Markov process to compute the abstraction separately for each dimension; second, we employ dynamic Bayesian networks (DBN) as compact representations of the abstraction. In contrast, approaches which represent and store the (exponentially large) Markov chain explicitly incur significantly higher memory requirements. In our experiments, explicit representations scaled to models of dimension less than half the size as those analyzable by DBN representations. We show how to construct a DBN abstraction of a Markov process satisfying an independence assumption on the driving process noise. We compute a guaranteed bound on the error in the abstraction w.r.t. the probabilistic invariance property--the dimension-dependent abstraction makes the error bounds more precise than existing approaches. Additionally, we show how factor graphs and the sum-product algorithm for DBNs can be used to solve the finite-horizon probabilistic invariance problem. Together, DBN-based representations and algorithms can be significantly more efficient than explicit representations of Markov chains for abstracting and model checking structured Markov processes.

Safraless LTL synthesis considering maximal realizability

Abstract: Linear temporal logic (LTL) synthesis is a formal method for automatically composing a reactive system that realizes a given behavioral specification described in LTL if the specification is realizable. Even if the whole specification is unrealizable, it is preferable to synthesize a best-effort reactive system. That is, a system that maximally realizes its partial specifications. Therefore, we categorized specifications into must specifications (which should never be violated) and desirable specifications (the violation of which may be unavoidable). In this paper, we propose a method for synthesizing a reactive system that realizes all must specifications and strongly endeavors to satisfy each desirable specification. The general form of the desirable specifications without assumptions is $$\mathbf{G }\varphi $$ , which means “ $$\varphi $$ always holds”. In our approach, the best effort to satisfy $$\mathbf{G }\varphi $$ is to maximize the number of steps satisfying $$\varphi $$ in the interaction. To quantitatively evaluate the number of steps, we used a mean-payoff objective based on LTL formulae. Our method applies the Safraless approach to construct safety games from given must and desirable specifications, where the must specification can be written in full LTL and may include assumptions. It then transforms the safety games constructed from the desirable specifications into mean-payoff games and finally composes a reactive system as an optimal strategy on a synchronized product of the games.

Pseudopolynomial iterative algorithm to solve total-payoff games and min-cost reachability games

Abstract: Quantitative games are two-player zero-sum games played on directed weighted graphs Total-payoff games--that can be seen as a refinement of the well-studied mean-payoff games--are the variant where the payoff of a play is computed as the sum of the weights Our aim is to describe the first pseudo-polynomial time algorithm for total-payoff games in the presence of arbitrary weights It consists of a non-trivial application of the value iteration paradigm Indeed, it requires to study, as a milestone, a refinement of these games, called min-cost reachability games, where we add a reachability objective to one of the players For these games, we give an efficient value iteration algorithm to compute the values and optimal strategies (when they exist), that runs in pseudo-polynomial time We also propose heuristics to speed up the computations

On the relations between Markov chain lumpability and reversibility

Abstract: In the literature, the notions of lumpability and time reversibility for large Markov chains have been widely used to efficiently study the functional and non-functional properties of computer systems. In this paper we explore the relations among different definitions of lumpability (strong, exact and strict) and the notion of time-reversed Markov chain. Specifically, we prove that an exact lumping induces a strong lumping on the reversed Markov chain and a strict lumping holds both for the forward and the reversed processes. Based on these results we introduce the class of $$\lambda \rho $$ -reversible Markov chains which combines the notions of lumping and time reversibility modulo state renaming. We show that the class of autoreversible processes, previously introduced in Marin and Rossi (Proceedings of the IEEE 21st international symposium on modeling, analysis and simulation of computer and telecommunication systems MASCOTS, pp. 151–160, 2013), is strictly contained in the class of $$\lambda \rho $$ -reversible chains.

Signature-free asynchronous Byzantine systems: from multivalued to binary consensus with $$t<n/3$$t<n/3, $$O(n^2)$$O(n2) messages, and constant time

Abstract: This paper presents a new algorithm that reduces multivalued consensus to binary consensus in an asynchronous message-passing system made up of n processes where up to t may commit Byzantine failures. This algorithm has the following noteworthy properties: it assumes t < n/3 (and is consequently optimal from a resilience point of view), uses $$O(n^2)$$O(n2) messages, has a constant time complexity, and uses neither signatures nor additional computational power (such as random numbers, failure detectors, additional scheduling assumption, or additional synchrony assumption). The design of this reduction algorithm relies on two new all-to-all communication abstractions. The first one allows the non-faulty processes to reduce the number of proposed values to c, where c is a small constant. The second communication abstraction allows each non-faulty process to compute a set of (proposed) values satisfying the following property: if the set of a non-faulty process is a singleton containing value v, the set of any non-faulty process contains v. Both communication abstractions have an $$O(n^2)$$O(n2) message complexity and a constant time complexity. The reduction of multivalued Byzantine consensus to binary Byzantine consensus is then a simple sequential use of these communication abstractions. To the best of our knowledge, this is the first asynchronous message-passing algorithm that reduces multivalued consensus to binary consensus with $$O(n^2)$$O(n2) messages and constant time complexity (measured with the longest causal chain of messages) in the presence of up to t < n/3 Byzantine processes, and without using cryptography techniques. Moreover, this reduction algorithm uses a single instance of the underlying binary consensus, and tolerates message re-ordering by Byzantine processes.

Reactive synthesis without regret

Abstract: Two-player zero-sum games of infinite duration and their quantitative versions are used in verification to model the interaction between a controller (Eve) and its environment (Adam). The question usually addressed is that of the existence (and computability) of a strategy for Eve that can maximize her payoff against any strategy of Adam. In this work, we are interested in strategies of Eve that minimize her regret, i.e. strategies that minimize the difference between her actual payoff and the payoff she could have achieved if she had known the strategy of Adam in advance. We give algorithms to compute the strategies of Eve that ensure minimal regret against an adversary whose choice of strategy is (1) unrestricted, (2) limited to positional strategies, or (3) limited to word strategies, and show that the two last cases have natural modelling applications. These results apply for quantitative games defined with the classical payoff functions $$\mathsf {Inf}$$Inf, $$\mathsf {Sup}$$Sup, $${\mathsf {LimInf}}$$LimInf, $$\mathsf {LimSup}$$LimSup, and mean-payoff. We also show that our notion of regret minimization in which Adam is limited to word strategies generalizes the notion of good for games introduced by Henzinger and Piterman, and is related to the notion of determinization by pruning due to Aminof, Kupferman and Lampert.

The Cult of 'Maria Regina' in Early Medieval Rome

Abstract: paper delivbered at the international conference on the theme of 'Mater Christi' (Rome, 7-9 October 2004)

Approximate counting in SMT and value estimation for probabilistic programs

Abstract: #SMT, or model counting for logical theories, is a well-known hard problem that generalizes such tasks as counting the number of satisfying assignments to a Boolean formula and computing the volume of a polytope. In the realm of satisfiability modulo theories (SMT) there is a growing need for model counting solvers, coming from several application domains (quantitative information flow, static analysis of probabilistic programs). In this paper, we show a reduction from an approximate version of #SMT to SMT. We focus on the theories of integer arithmetic and linear real arithmetic. We propose model counting algorithms that provide approximate solutions with formal bounds on the approximation error. They run in polynomial time and make a polynomial number of queries to the SMT solver for the underlying theory, exploiting “for free” the sophisticated heuristics implemented within modern SMT solvers. We have implemented the algorithms and used them to solve the value problem for a model of loop-free probabilistic programs with nondeterminism.

Efficiently solving the Bin Packing problem through bio-inspired mobility

Abstract: Recently we have considered the possibility of using bio-inspired mobility for solving a weak NP-complete problem (Partition). In this paper we provide a semi-uniform polynomial solution for a strong NP-complete problem (Bin Packing) by means of membrane computing techniques. The solution employs mobile membranes and elementary membrane division.

Model checking the evolution of gene regulatory networks

Abstract: The behaviour of gene regulatory networks (GRNs) is typically analysed using simulation-based statistical testing-like methods. In this paper, we demonstrate that we can replace this approach by a formal verification-like method that gives higher assurance and scalability. We focus on Wagner’s weighted GRN model with varying weights, which is used in evolutionary biology. In the model, weight parameters represent the gene interaction strength that may change due to genetic mutations. For a property of interest, we synthesise the constraints over the parameter space that represent the set of GRNs satisfying the property. We experimentally show that our parameter synthesis procedure computes the mutational robustness of GRNs—an important problem of interest in evolutionary biology—more efficiently than the classical simulation method. We specify the property in linear temporal logic. We employ symbolic bounded model checking and SMT solving to compute the space of GRNs that satisfy the property, which amounts to synthesizing a set of linear constraints on the weights.

Pembiayaan usaha mikro, kecil, dan menengah melalui situs crowdfunding “patungan.net” dikaitkan dengan undang-undang nomor 20 tahun 2008 tentang usaha mikro, kecil, dan menengah

Abstract: ABSTRAK Keterbatasan mengakses bantuan permodalan merupakan salah satu persoalan yang dihadapi sebagian besar pelaku usaha, termasuk UMKM. Pada praktiknya, saat ini berkembang kegiatan penggalangan dana masyarakat secara online melalui situs crowdfunding yang ditujukan untuk pembiayaan UMKM. Tulisan ini merupakan hasil dari penelitian yang telah selesai dilakukan untuk mengetahui dan mengkaji legalitas pembiayaan UMKM yang bersumber dari penggalangan dana secara online melalui situs Patungan.net serta sejauh mana tanggung jawab pengelola situs Patungan.net sebagai perantara pelaku UMKM selaku pemilik proyek dan suporter dalam hal tidak ada kontrak yang menjadi dasar hubungan hukum dalam pembiayaan UMKM. Sebagai bagian dari penelitian yuridis normatif yang dianalisis secara yuridis normatif, hasil yang didapat sebagai kesimpulan yaitu bahwa pembiayaan UMKM yang bersumber dari penggalangan dana masyarakat melalui situs crowdfunding Patungan.net tidak legal karena berdasarkan ketentuan Pasal 1 angka 11 Undang-Undang Nomor 20 Tahun 2008 tentang Usaha Mikro, Kecil, dan Menengah. Tanggung jawab pengelola situs Patungan.net sebagai perantara dengan suporter tidak hanya terbatas pada kewajiban menyerahkan donasi yang terkumpul kepada pelaku UMKM apabila penggalangan dana berhasil mencapai target atau kewajiban untuk mengembalikan donasi yang terkumpul kepada masing-masing suporter apabila penggalangan dana gagal mencapai target, tetapi adanya lastgeving antara pengelola situs dengan pelaku UMKM yang terjadi dengan sendirinya sesuai ketentuan Pasal 1793 KUHPerdata, maka harus bertanggung jawab melaporkan transparansi dana yang terkumpul selama penggalangan dana berlangsung berdasarkan Pasal 1802 KUHPerdata. Kata kunci: Crowfunding, Pembiayaan, Usaha Mikro Kecil Menengah.

Reversible Watson---Crick automata

Abstract: Since 1970, reversible finite automata have generated interest among researcher; but till now, we have not come across a model of reversible read only one-way finite automata which accept all regular languages, In this paper, we introduce a new model of one-way reversible finite automata inspired by the Watson---Crick complementarity relation and show that our model can accept all regular languages. We further show that our model accepts a language which is not accepted by any multi-head deterministic finite automaton.

Immagini di Maria nella pittura e nei mosaici romani dalla crisi monotelita agli inizi della seconda iconoclastia (640-819)

Abstract: L’articolo analizza le immagini della Vergine, pittoriche e musive, presenti a Roma dalla meta del VII secolo ai primi decenni del IX. Il taglio prescelto cerca di usare in parallelo le diverse chiavi interpretative proposte dalla storiografia: l’analisi storica, le ricerche iconografico-iconologiche, le letture stilistico-formali. Nelle rappresentazioni di Maria si riflettono le dinamiche religiose dello sviluppo dottrinale e della pratica devozionale, legate prima alla eresia monotelita poi alla crisi iconoclasta; in seguito in esse convergono nuovi significati politici connessi alla nascente ideologia dello Stato della Chiesa. Lo sviluppo delle immagini mariane mostra nel corso dei quasi duecento anni esaminati il progressivo distacco dalla cultura bizantina ed il profilarsi di una nuova identita culturale.

Compositional schedulability analysis of real-time actor-based systems

Abstract: We present an extension of the actor model with real-time, including deadlines associated with messages, and explicit application-level scheduling policies, e.g.,"earliest deadline first" which can be associated with individual actors. Schedulability analysis in this setting amounts to checking whether, given a scheduling policy for each actor, every task is processed within its designated deadline. To check schedulability, we introduce a compositional automata-theoretic approach, based on maximal use of model checking combined with testing. Behavioral interfaces define what an actor expects from the environment, and the deadlines for messages given these assumptions. We use model checking to verify that actors match their behavioral interfaces. We extend timed automata refinement with the notion of deadlines and use it to define compatibility of actor environments with the behavioral interfaces. Model checking of compatibility is computationally hard, so we propose a special testing process. We show that the analyses are decidable and automate the process using the Uppaal model checker.

Kewenangan pengaturan dan pengawasan perbankan oleh bank indonesia dan otoritas jasa keuangan (ojk)

Abstract: ABSTRAK Studi ini menganalisis kewenangan pengaturan dan pengawasan perbankan yang dilakukan oleh Otoritas Jasa Keuangan yang di atur dalam Undang Undang No. 21 Tahun 2011 yang sebelumnya dilakukan oleh Bank Indonesia sesungguhnya untuk menerapkan prinsip kehati-hatian dan prinsip itikad baik pada perbankan dalam rangka mencegah resiko terhadap adanya tindak pidana perbankan. Pengawasan dan pengaturan perbankan setelah keluarnya Undang Undang OJK (Otoritas Jasa Keuangan), Bank Indonesia sebagai bank sentral hanya berperan sebagai regulator kebijakan moneter untuk menjaga stabilitas moneter. Permasalahan dalam penelitian ini adalah mengenai konsep hukum pengaturan dan pengawasan sektor perbankan oleh OJK dan bagaimana hubungan hukum dengan Bank Indonesia. Jenis penelitian yang digunakan adalah yuridis normatif, selanjutnya data yang digunakan data sekunder dan data primer, pendekatan dalam penelitian ini menggunakan pendekatan konseptual, dan komporatif. Kewenangan tugas pengaturan dan pengawasan perbankan oleh Bank Indonesia yang dialihkan ke Otoritas Jasa Keuangan hanya yang berkaitan dengan microprudential, dan pengaturan perbankan oleh Bank Indonesia tetap dilakukan oleh Bank Indonesia hanya macroprudential, sedangkan pengaturan perbankan oleh Otoritas Jasa Keuangan tidak sepenuhnya secara indenpenden. Kata kunci: Bank Indonesia, hubungan hukum, kewenangan, Otoritas Jasa Keuangan. ABSTRACT This study analyzes the regulatory and supervisory authority of banks conducted by the Financial Services Authority set out in Law no. 21 of 2011 which was previously undertaken by Bank Indonesia in fact to apply the principles of prudence and good faith principles to banks in order to prevent the risk of banking crime. Banking supervision and regulation after the issuance of the OJK Law (Financial Services Authority), Bank Indonesia as the central bank only acts as a monetary policy regulator to maintain monetary stability. The problem in this research is about the concept of law of regulation and supervision of banking sector by OJK and how the legal relationship with Bank Indonesia. The type of research used is juridical normative, then the data used secondary data and primary data, the approach in this study using conceptual approach, and komporatif. Bank Indonesia’s regulatory and supervisory duties transferred to OJK are only related to microprudential, and the banking arrangements by Bank Indonesia are still conducted by Bank Indonesia only macroprudential, while the regulation of banking by OJK is not fully independent. Keywords: authority, Bank Indonesia, legal relations and the Financial Services Authority

Characteristic bisimulation for higher-order session processes

Abstract: For higher-order (process) languages, characterising contextual equivalence is a long-standing issue. In the setting of a higher-order $$\pi $$ź-calculus with session types, we develop characteristic bisimilarity, a typed bisimilarity which fully characterises contextual equivalence. To our knowledge, ours is the first characterisation of its kind. Using simple values inhabiting (session) types, our approach distinguishes from untyped methods for characterising contextual equivalence in higher-order processes: we show that observing as inputs only a precise finite set of higher-order values suffices to reason about higher-order session processes. We demonstrate how characteristic bisimilarity can be used to justify optimisations in session protocols with mobile code communication.

Symblicit algorithms for mean-payoff and shortest path in monotonic Markov decision processes

Abstract: When treating Markov decision processes (MDPs) with large state spaces, using explicit representations quickly becomes unfeasible. Lately, Wimmer et al. have proposed a so-called symblicit algorithm for the synthesis of optimal strategies in MDPs, in the quantitative setting of expected mean-payoff. This algorithm, based on the strategy iteration algorithm of Howard and Veinott, efficiently combines symbolic and explicit data structures, and uses binary decision diagrams as symbolic representation. The aim of this paper is to show that the new data structure of pseudo-antichains (an extension of antichains) provides another interesting alternative, especially for the class of monotonic MDPs. We design efficient pseudo-antichain based symblicit algorithms (with open source implementations) for two quantitative settings: the expected mean-payoff and the stochastic shortest path. For two practical applications coming from automated planning and $$\mathsf {LTL}$$ synthesis, we report promising experimental results w.r.t. both the run time and the memory consumption. We also show that a variant of pseudo-antichains allows to handle the infinite state spaces underlying the qualitative verification of probabilistic lossy channel systems.

Kompetencije učenika i nastavnika za 21. stoljeće

Abstract: The paper reflects on the competencies necessary for quality and productive life in the 21st centurywhich is marked by the widespread use of ICT in all areas of life and work. It gives an overviewof the different models of competencies in witch, by the developed IT skills and informationliteracy, there are also a wider competencies such as, for example, those of communication,cooperation, competence for creative and critical thinking and problem solving, etc. Specialattention is devoted to the identification of recent students’ and teachers’ skills and competenciesthat support teaching and learning and that are further developing through the contemporaryopen class. For teachers, to be able to effectively integrate ICT in class process of learning andteaching, it is necessary that they have built two types of skills and competencies: at least thebasic skills of information literacy and multimedia didactic competencies. While teachers candevelop the basic technological skills through the common computer courses for the generalpublic, building multimedia didactic competence requires specialized teachers’ training, which isgeared towards the specific methods of ICT use in teaching. Competences represent a dynamicphenomenon caused by the characteristics of a particular context and variable over time, so it isvitally to continuously reflect on the skills and competencies necessary for life in the 21st century.

Adolescenti i školski stres

Abstract: The most common source of stress within adolescents is connected with school, conflicts with parents and friends. The goal of this thesis is to express literature views and researches that are dealing with school stress within the adolescents. In order to approach the problem of school stress within adolescents it is shown the sample of what is causing the school stress, strategy of confrontation of adolescents with stress, and the role of preventive programs as one of the most efficient ways of facing and detracting certain risky factors at school. Based on analysis of available researches, it is visible that, no matter the age and sexual differences a negative mark or mark lower than expected, represents specific and most usual source of stress that is visible with adolescents, and that there is a difference in perception of stress in the manner that priorities and sources of stress are different within adolescents in high school and elementary school. Exactly those sources of stress cause many psychosomatic disorders and/or emotional reactions with adolescents; because of what school stress represents a very serious problem. One of the most efficient ways of facing and detracting of certain risky factors at school is creating and realizing of preventive programs. Also, the quality of relationship that the teacher creates with adolescent person is extremely important in reducing of negative influence of school stress on adolescents, as well as achieving efficient conditions of learning and teaching.

Disjunctivity and other properties of sets of pseudo-bordered words

Abstract: The concepts of pseudo-bordered and pseudo-unbordered words are in large part motivated by research in theoretical DNA computing, wherein the Watson---Crick complementarity of DNA strands is modelled as an antimorphic involution, that is, a function $$\theta $$ź which is an antimorphism, $$\theta (uv)=\theta (v) \theta (u)$$ź(uv)=ź(v)ź(u), and an involution, $$\theta (\theta (u))=u$$ź(ź(u))=u, for all words u, v over the DNA alphabet. In particular, a word w is said to be $$\theta $$ź-bordered (or pseudo-bordered) if there exists a word $$v \in \Sigma ^{+}$$vźΣ+ that is a proper prefix of w, while $$\theta (v)$$ź(v) is a proper suffix of w. A word which is not $$\theta $$ź-bordered is $$\theta $$ź-unbordered. This paper continues the exploration of properties (for the case where $$\theta $$ź is a morphic involution) of the set of $$\theta $$ź-unbordered words, $$D_{\theta }(1)$$Dź(1), and the sets of words that have exactly i$$\theta $$ź-borders, $$D_{\theta }(i)$$Dź(i), $$i \ge 2$$iź2. We prove that, under some conditions, the set $$D_{\theta }(i)$$Dź(i) is disjunctive for all $$i \ge 1$$iź1, and that the set $$D_{\theta }^i(1){\setminus }D(i)$$Dźi(1)\D(i) is disjunctive for all $$i\ge 2$$iź2, where D(i) denotes the set of words with exactly i borders. We also discuss conditions for catenations of languages of $$\theta $$ź-unbordered words to remain $$\theta $$ź-unbordered, and anticipate further generalizations by showing that the set of all $$\theta $$ź-bordered words is not context-free for all morphisms $$\theta $$ź over an alphabet $$\Sigma $$Σ with $$|\Sigma | \ge 3$$|Σ|ź3 such that $$\theta (a) e a$$ź(a)źa for all $$a \in \Sigma $$aźΣ and $$\theta ^{3}$$ź3 equals the identity function on $$\Sigma $$Σ.