In the modern era of multi-core systems, the main aim is to utilize the cores properly. This utilization can be done by concurrent programming. But developing a flawless and well-organized concurrent program is difficult. Software Transactional Memory Systems (STMs) are a convenient programming interface which assist the programmer to access the shared memory concurrently without worrying about consistency

We investigate exploration algorithms for autonomous mobile robots evolving in uniform ring-shaped networks. Different from the usual Look-Compute-Move (LCM) model, we consider two characteristics: myopia and luminosity. Myopia means each robot has a limited visibility. We consider the weakest assumption for myopia: each robot can only observe its neighboring nodes. Luminosity means each robot maintains

We consider search in an unknown finite 2D square grid by a metamorphic robotic system consisting of anonymous memory-less modules. Each module autonomously moves while executing a common distributed algorithm and the modules collectively form a robotic system by keeping connectivity. The number of shapes of the metamorphic robotic system grows as the number of modules increases, and a shape of the

We present LB-Spiral, a novel distributed directory protocol for shared objects, suitable for large-scale distributed shared memory systems. Each shared object has an owner node that can modify its value. The ownership may change by moving the object from one node to another in response to move requests. The value of an object can be read by other nodes with lookup requests. The distinctive feature

We consider the fundamental problem of arranging a set of n autonomous robots (points) on a real plane according to an arbitrary given pattern. Each robot operates in a, largely oblivious, look-compute-move step. We measure the time complexity of our algorithms in “epochs,” which denotes the minimum time interval in which every robot performs at least one look-compute-move step. We present a framework

We study the problems of leader election and population size counting for population protocols: networks of finite-state anonymous agents that interact randomly under a uniform random scheduler. We provide simple protocols for approximate counting of the size of the population and for leader election. We show a protocol for leader election that terminates in O(log2⁡nlog⁡m) parallel time, where m is

While a lot of research in distributed computing has covered solutions for self-stabilizing computing and topologies, there is far less work on self-stabilization for distributed data structures. Considering crashing peers in peer-to-peer networks, it should not be taken for granted that a distributed data structure remains intact. In this work, we present a self-stabilizing protocol for a distributed

We consider the state machine replication problem in semi-synchronous systems subject to Byzantine server failures. We propose a new solution to the problem in the form of a protocol for the generalized consensus problem. The protocol solves the consensus problem in a setting in which information about conflicts between transactions is available (such information can be in the form of transaction read

Quantum computation has emerged as a powerful computational medium of our time, having demonstrated the remarkable efficiency in factoring a positive integer and searching databases faster than any currently known classical computing algorithm. Adiabatic evolution of quantum systems have been studied as a potential means that physically realizes quantum computation. Up to now, all the research on adiabatic

Right-one way jumping finite automata are deterministic devices that process their input in a discontinuous fashion. We generalise these devices to nondeterministic machines. More precisely we study the impact on the computational power of these machines when allowing multiple initial states and/or a nondeterministic transition function including spontaneous or λ-transitions. We show inclusion relations

We compute the exact maximum state complexity for the language consisting of m words of length N, and characterize languages achieving the maximum. We also consider a special case, namely languages C(w) consisting of the conjugates of a single word w. The words for which the maximum state complexity of C(w) is achieved turn out to be a natural generalization of de Bruijn words. We show that generalized

Union-free languages are described by regular expressions using only concatenation and Kleene-star. Every regular language can be given as a union of finitely many union-free languages. By the minimal number of union-free languages needed in such union-free decompositions of a regular language, its union-complexity is defined. In this paper, the union-complexity of the languages obtained by various

We introduce the deterministic computational model of an iterated uniform finite-state transducer (iufst). An iufst performs the same length-preserving transduction on several left-to-right sweeps. The first sweep takes place on the input string, while any other sweep processes the output of the previous one. The iufst accepts by halting at the end of a sweep in an accepting state. First, we focus

The paper investigates the state complexity of two operations on regular languages, known as GF(2)-concatenation and GF(2)-inverse of Bakinova et al. (2018) [1], in the case of a one-symbol alphabet. The GF(2)-concatenation is a variant of the classical concatenation obtained by replacing Boolean logic in its definition with the GF(2) field; it is proved that GF(2)-concatenation of two unary languages

In matrix grammars, context-free rules have to be applied in a certain order. However in simple semi-conditional (SSC) grammars, the derivations are controlled either by a permitting string or by a forbidden string associated to each rule. Typical descriptional complexity measures incorporate the number of nonterminals and the number of rules per matrix in a matrix grammar. In SSC grammars, the maximum

Tree width (respectively, string path width) measures the maximal number of partial (respectively, complete) computations of a nondeterministic finite automaton on an input of given length. We characterize polynomial and exponential growth rates of tree width and string path width by structural properties of the corresponding nondeterministic finite automaton (NFA). As the main result we show that

Maximally parallel manner is a usual rule application strategy for P systems, where a maximal set of enabled rules are chosen and each rule in the set is applied as many times as possible. In this work, we consider a rule application strategy, rule synchronization, where some synchronization sets of rules are given, a rule in a synchronization set of rules can be applied only if all rules in the set

In this paper, we propose a novel algorithm to learn a Büchi automaton from a teacher who knows an ω-regular language. The learned Büchi automaton can be a nondeterministic Büchi automaton or a limit deterministic Büchi automaton. The learning algorithm is based on learning a formalism called family of DFAs (FDFAs) recently proposed by Angluin and Fisman. The main catch is that we use a classification

In this paper, we study Reiter's propositional default logic when the treewidth of a certain graph representation (semi-primal graph) of the input theory is bounded. We establish a dynamic programming algorithm on tree decompositions that decides whether a theory has a consistent stable extension ( Cons ). Our algorithm can even be used to enumerate all generating defaults ( EnumSD ) that lead to stable

Reset Petri nets are a particular class of Petri nets where transition firings can remove all tokens from a place without checking if this place actually holds tokens or not. In this paper we look at partial order semantics of reset Petri nets. In particular, we propose a pomset bisimulation for comparing their concurrent behaviours. Building on this pomset bisimulation we then propose a generalization

We investigate the function L(h,p,q), called here the length function, such that L(h,p,q) is the minimum length which guarantees that a natural extension of the periodicity lemma is valid for partial words with h holes and (so-called strong) periods p,q. In a series of papers, the formulae for the length function, in terms of p and q, were provided for each fixed h≤7. We demystify the generic structure

The paper is focused on automata and linear temporal logics for describing the behaviour of real-time pushdown reactive systems. The goal of the paper is to bridge (both in the context of automata and linear temporal logics) tractable formalisms specialized for expressing separately dense-time real-time properties and context-free properties though preserving tractability in the combined setting. As

Variants of the union and concatenation operations on formal languages are investigated, in which Boolean logic in the definitions (that is, conjunction and disjunction) is replaced with the operations in the two-element field GF(2) (conjunction and exclusive OR). Union is thus replaced with symmetric difference, whereas concatenation gives rise to a new GF(2)-concatenation operation, which is notable

The learners considered in this paper process an infinite text of data containing all members of the set to be learnt in cycles, one word in each cycle, and maintain as a long term memory a string which provides all internal data the learner can use in the next cycle. Updating of these strings is usually done by either recursive or automatic learners. The present work looks at transduced learners,

Graph-walking automata (GWA) are finite-state devices that traverse graphs given as an input by following their edges; they have been studied both as a theoretical notion and as a model of pathfinding in robotics. If a graph is regarded as the set of memory configurations of a certain abstract machine, then various families of devices can be described as GWA: such are two-way finite automata, their

A Two-Party Authenticated Key Agreement (2-PAKA) protocol facilitates two communicating entities to equally contribute to the establishment of a shared session key. IDentity-based 2-PAKA (ID-2-PAKA) protocols are widely researched, since it eliminates the need for explicit public-key verification using digital certificates. Over the years, ID-2-PAKA protocols with perfect forward secrecy and Key Generation

In this work, we present the first secure stegosystem in the common computational model which, for any communication channel, is provably secure, reliable, and has nearly optimal bandwidth, but needs super-polynomial time. This solves several open problems about secret-key steganography in the computational model. In particular, our result answers affirmatively the question whether there exists a secure

We formalize and examine the online Dictionary Recognition with One Gap problem (DROG) which is the following. Preprocess a dictionary D of d patterns each containing a special gap symbol that matches any string, so that given a text arriving online a character at a time, all patterns from D which are suffixes of the text that has arrived so far and have not been reported yet, are reported before the

This paper investigates the model of probabilistic program with delays (PPD) that consists of a few program blocks. Performing each block has an additional time-consumption—waiting to be executed—besides the running time. We interpret the operational semantics of PPD by Markov automata with a cost structure on transitions. Our goal is to measure those individual execution paths of a PPD that terminates

We study a class of quantitative models for higher-order computation: Lafont categories with (infinite) biproducts. Each of these has a complete “internal semiring” and can be enriched over its modules. We describe a semantics of nondeterministic PCF weighted over this semiring in which fixed points are obtained from the bifree algebra over its exponential structure. By characterizing them concretely

This paper introduces a new inequality in algorithmic information theory that can be seen as an extended coding theorem. This inequality has applications in new bounds between quantum complexity measures.

This paper presents a study of causality in a reversible, concurrent setting. There exist various notions of causality in π-calculus, which differ in the treatment of parallel extrusions of the same name. Hence, by using a parametric way of bookkeeping the order and the dependencies among extruders it is possible to map different causal semantics into the same framework. Starting from this simple observation

We study edit distances between strings, based on weighted operations such as character substitutions, insertions, deletions and additionally consolidations and fragmentations. The two latter operations transform a sequence of characters into one character and vice-versa. They correspond to the compression and expansion in Dynamic Time-Warping algorithms for speech recognition and are also used for

In the last years renewed investigation of operator precedence languages (OPL) led to discover important properties thereof: OPL are closed with respect to all major operations, are characterized, besides by the original grammar family, in terms of an automata family (OPA) and an MSO logic; furthermore they significantly generalize the well-known visibly pushdown languages (VPL). A different area of

We define a Syntactic Stochastic Process (SSP) as a stochastic process valued in the set of terminal symbols of a grammar, and whose realizations are terminal strings generated by some stochastic grammar. We consider first the case of a Stochastic Context-Free Grammar (SCFGs) generating the process and show that any SSP generated by an SCFG (a context free process) can be consistently indexed by a

We study the role of randomness in the broadcast congested clique model. This is message-passing model of distributed computation where the nodes of a network know their local neighborhoods and they broadcast, in synchronous rounds, messages that are visible to every other node. This works aims to separate three different settings: deterministic protocols, randomized protocols with private coins, and

The reputation of a process is based on its past and present behaviour; it evolves in time depending on several factors including the actions performed, the reputation of its interacting processes and locations where the process resides. We design a calculus of mobile agents in distributed systems able to handle the dynamics of reputation which changes over time depending on specified factors. The

Nonconstructive computations by various types of machines and automata have been considered by, for example, Karp and Lipton [21], and Freivalds [9], [10]. They allow to regard more complicated algorithms from the viewpoint of much more primitive computational devices. The amount of nonconstructivity is a quantitative characterization of the distance between types of computational devices with respect

Context-free languages of infinite words have recently found increasing interest. Here, we will present a second-order logic with the same expressive power as Büchi or Muller pushdown automata for infinite words. This extends fundamental logical characterizations of Büchi, Elgot, Trakhtenbrot for regular languages of finite and infinite words and a more recent logical characterization of Lautemann

Probabilistic automata are an extension of nondeterministic finite automata in which transitions are annotated with probabilities. Despite its simplicity, this model is very expressive and many of the associated algorithmic questions are undecidable. In this work we focus on the emptiness problem (and its variant the value problem), which asks whether a given probabilistic automaton accepts some word

Functional MSO transductions, deterministic two-way transducers, as well as streaming string transducers are all equivalent models for regular functions. In this paper, we show that every regular function, either on finite words or on infinite words, captured by a deterministic two-way transducer, can be described with a regular transducer expression (RTE ). For infinite words, the two-way transducer

We develop a new bisimulation (pseudo)metric for weighted finite automata (WFA) that generalizes Boreale's linear bisimulation relation. Our metrics are induced by seminorms on the state space of WFA. Our development is based on spectral properties of sets of linear operators. In particular, the joint spectral radius of the transition matrices of WFA plays a central role. We also study continuity properties

We consider Pareto analysis of reachable states in multi-priced timed automata (MPTA). An MPTA is a timed automaton equipped with multiple observers that record costs (to be minimised) and rewards (to be maximised) that are accumulated along a computation. Each observer has a non-negative derivative that is constant in each location of the automaton. We study the Pareto Domination Problem, which asks

We introduce semiring-weighted regular tree grammars with storage where the semiring is complete. We show that the class of weighted tree languages generated by them is a principal abstract family of weighted tree languages provided that the semiring is commutative, the rank of symbols occurring in trees is bounded by a global parameter, and that the storage is finitely encoded and contains a reset

We consider input deterministic finite state transducers with infinite inputs and infinite outputs, and we consider the property of Borel normality on infinite words. When these transducers are given by a strongly connected set of states, and when the input is a Borel normal sequence, the output is an infinite word such that every word has a frequency given by a weighted automaton over the rationals

We introduce and investigate a weighted propositional configuration logic over commutative semirings. Our logic is intended to serve as a specification language for software architectures with quantitative features. We prove an efficient construction of full normal forms and decidability of equivalence of formulas in this logic. We illustrate the motivation of this work by describing well-known architectures

Weighted automata map input words to numerical values. Applications of weighted automata include formal verification of quantitative properties, as well as text, speech, and image processing. In the 90's, Krob studied the decidability of problems on rational series, which strongly relate to weighted automata. In particular, it follows from Krob's results that the universality problem (that is, deciding

This paper studies the following approximate minimization problem: given a minimal weighted tree automaton A with n states recognizing a weighted tree language f, can we construct a smaller automaton Aˆ with nˆ

We present a modal logic for subject-oriented representation and reasoning about a two-dimensional space. The space is represented with the polar coordinate system where the central point is occupied by the subject and modal operators are interpreted by relations defined relatively to the position and orientation of the subject, namely ‘outwards’, ‘inwards’, ‘clockwise’, ‘counter-clockwise’, and transitive

The model checking (MC) problem for Halpern and Shoham's interval temporal logic HS has been recently investigated in a systematic way, and it is known to be decidable. An intriguing open question is the exact complexity of the problem for full HS: it is at least EXPSPACE-hard, and the only known upper bound, which has been obtained by exploiting an abstract representation of Kripke structure paths

A Simple Temporal Network (STN) consists of time points modeling temporal events and constraints modeling the minimal and maximal temporal distance between them. A Simple Temporal Network with Decisions (STND) extends an STN by adding decision time points to model temporal plans with decisions. A decision time point is a special kind of time point that once executed allows for deciding a truth value

We study the satisfiability and model-checking problems for timed hyperproperties specified with HyperMITL, a timed extension of HyperLTL. While the satisfiability problem can be solved similarly as for HyperLTL, we show that the model-checking problem for HyperMITL, unless the specification is alternation-free, is undecidable even when very restricted timing constraints are allowed. On the positive

Given a qualitative constraint network (QCN), a singleton-style consistency is a local consistency that focuses on each base relation (atom) of a constraint separately, rather than the entire constraint altogether. More technically, such a consistency verifies if each base relation of each constraint of a QCN can serve as a support with respect to the closure of that network under a (naturally) weaker

This paper analyses a selection of articles from European transport regulations that contain algorithmic information, but may be problematic to implement. We focus on issues regarding the interpretation of tachograph data and requirements on weekly rest periods. We first show that the interpretation of data prescribed by these regulations is highly sensitive to minor variations in input, such that

Quantified CTL (QCTL) extends the temporal logic CTL with quantifications over atomic propositions. This extension is known to be very expressive: QCTL allows us to express complex properties over Kripke structures (it is as expressive as MSO). Several semantics exist for the quantifications: here, we work with the structure semantics, where the extra propositions label the Kripke structure (and not

First-Order Linear Temporal Logic (FOLTL) and its Many-Sorted variant (MSFOLTL) are well-suited to specify infinite-state systems. However, the satisfiability of (MS)FOLTL is not even semi-decidable, thus preventing automated verification. In this paper, we exhibit various fragments of increasing scope that provide a pertinent basis for the abstract specification of infinite-state systems. We show

Weighted counting problems are a natural generalization of counting problems where a weight is associated with every computational path of polynomial-time non-deterministic Turing machines. The goal is to compute the sum of weights of all paths (instead of number of accepting paths). Useful properties and plenty of applications make them interesting. The definition captures even undecidable problems

Motivated by applications in bioinformatics and image searching, in what follows, we study the classic pattern matching problem in the context of elastic-degenerate strings: the generalised notion of gapped strings. An elastic-degenerate string can been seen as an ordered collection of k strings interleaved by k−1 elastic-degenerate symbols, where each such elastic-degenerate symbol corresponds to

A variant of adaptive arithmetic coding is proposed, adding cryptographic features to this classical compression method. The idea is to perform the updates of the frequency tables for characters of the underlying alphabet selectively, according to some randomly chosen secret key K. We give empirical evidence that with reasonably chosen parameters, the compression performance is not hurt, and discuss

The notion of latent-variable probabilistic context-free derivation of syntactic structures is enhanced to allow heads and unrestricted discontinuities. The chosen formalization covers both constituency parsing and dependency parsing. By the new framework, one obtains a probability distribution over the space of all discontinuous parses. This lends itself to intrinsic evaluation in terms of cross-entropy