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1

Decidability of addition and Frobenius map for polynomials and rational functions

Chompitaki Dimitra, Kamarianakis Manos, Pheidas Thanases

Reports on Mathematical Logic

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2022

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Vol. 57

53--60

EN

Let p be a prime number, Fp a finite field with p elements, F an algebraic extension of Fp and z a variable. We consider the structure of addition and the Frobenius map (i.e., x 7→ x p ) in the polynomial rings F[z] and in fields F(z) of rational functions. We prove that any question about F[z] in the structure of addition and Frobenius map may be effectively reduced to questions about the similar structure of the field F. Furthermore, we provide an example which shows that a fact which is true for addition and the Frobenius map in the polynomial rings F[z] fails to be true in F(z). As a consequence, certain methods used to prove model completeness for polynomials do not suffice to prove model completeness for similar structures for fields of rational functions F(z), a problem that remains open even for F = Fp

2

Resource Bisimilarity in Petri Nets is Decidable

Lomazova Irina, Bashkin Vladimir, Jančar Petr

Fundamenta Informaticae

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2022

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Vol. 186, nr 1-4

175--194

EN

Petri nets are a popular formalism for modeling and analyzing distributed systems. Tokens in Petri net models can represent the control flow state or resources produced/consumed by transition firings. We define a resource as a part (a submultiset) of Petri net markings and call two resources equivalent when replacing one of them with another in any marking does not change the observable Petri net behavior. We consider resource similarity and resource bisimilarity, two congruent restrictions of bisimulation equivalence on Petri net markings. Previously it was proved that resource similarity (the largest congruence included in bisimulation equivalence) is undecidable. Here we present an algorithm for checking resource bisimilarity, thereby proving that this relation (the largest congruence included in bisimulation equivalence that is a bisimulation) is decidable. We also give an example of two resources in a Petri net that are similar but not bisimilar.

3

Residuated Algebraic Structures in the Vicinity of Pre-rough Algebra and Decidability

Lin Zhe, Chakraborty Mihir Kumar, Ma Minghui

Fundamenta Informaticae

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2021

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Vol. 179, nr 3

239--274

EN

Varieties of topological quasi-Boolean algebras in the vicinity of pre-rough algebras [28, 29] are expanded to residuated algebraic structures by introducing a new implication operation and its residual in these structures. Sequent calculi for some classes of residuated algebraic structures are established. These sequent calculi have the strong finite model property which yields the decidability of the word problem for corresponding classes of algebraic structures.

4

Freeness Problem for Matrix Semigroups of Parikh Matrices

Teh Wen Chean, Atanasiu Adrian, Wong Denis C. K.

Fundamenta Informaticae

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2021

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Vol. 179, nr 4

385--397

EN

Since the undecidability of the mortality problem for 3 × 3 matrices over integers was proved using the Post Correspondence Problem, various studies on decision problems of matrix semigroups have emerged. The freeness problem in particular has received much attention but decidability remains open even for 2 × 2 upper triangular matrices over nonnegative integers. Parikh matrices are upper triangular matrices introduced as a generalization of Parikh vectors and have become useful tools in studying of subword occurrences. In this work, we focus on semigroups of Parikh matrices and study the freeness problem in this context.

5

The progress of science from a computational point of view: the drive towards ever higher solvability

Marciszewski Witold

Foundations of Computing and Decision Sciences

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2019

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Vol. 44, No. 1

11--26

EN

This essay's content is rendered by the titles of the successive sections. 1. Effective solvability versus intuitive solvability. — 2. Decidability, i.e. effective solvability, in predicate logic. The speedup phenomenon — 3. Contributions of the second-order logic to the problems of solvability — 4. The infinite progress of science in the light of Turing's idea of the oracle. The term "oracle" is a technical counterpart of the notion of mathematical intuition. A more detailed summary can be obtained through juxtaposing the textboxes labelled with letters A...F. Conclusion: in the progress of science an essential role is played by the feedback between intellectual intuitions (intuitive solvability) and algorithmic procedures (effective solvability).

6

Vector Ambiguity and Freeness Problems in SL (2, Z)

Ko S.-K., Potapov I.

Fundamenta Informaticae

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2018

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Vol. 162, nr 2/3

161--182

EN

We study the vector ambiguity problem and the vector freeness problem in SL (2, Z). Given a finitely generated n x n matrix semigroup S and an n-dimensional vector x, the vector ambiguity problem is to decide whether for every target vector y = Mx, where M ∈ S, M is unique. We also consider the vector freeness problem which is to show that every matrix M which is transforming x to Mx has a unique factorization with respect to the generator of S. We show that both problems are NP-complete in SL (2, Z), which is the set of 2 x 2 integer matrices with determinant 1. Moreover, we generalize the vector ambiguity problem and extend to the finite and k-vector ambiguity problems where we consider the degree of vector ambiguity of matrix semigroups.

7

Pure Strategies in Imperfect Information Stochastic Games

Carayol A., Löding C., Serre O.

Fundamenta Informaticae

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2018

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Vol. 160, nr 4

361--384

EN

We consider imperfect information stochastic games where we require the players to use pure (i.e. non randomised) strategies. We consider reachability, safety, Büchi and co-Büchi objectives, and investigate the existence of almost-sure/positively winning strategies for the first player when the second player is perfectly informed or more informed than the first player. We obtain decidability results for positive reachability and almost-sure Büchi with optimal algorithms to decide existence of a pure winning strategy and to compute one if it exists. We complete the picture by showing that positive safety is undecidable when restricting to pure strategies even if the second player is perfectly informed.

8

On Axiomatizability of the Multiplicative Theory of Numbers

Salehi S.

Fundamenta Informaticae

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2018

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Vol. 159, nr 3

279--296

EN

The multiplicative theory of a set of numbers (which could be natural, integer, rational, real or complex numbers) is the first-order theory of the structure of that set with (solely) the multiplication operation (that set is taken to be multiplicative, i.e., closed under multiplication). In this paper we study the multiplicative theories of the complex, real and (positive) rational numbers. These theories (and also the multiplicative theories of natural and integer numbers) are known to be decidable (i.e., there exists an algorithm that decides whether a given sentence is derivable form the theory); here we present explicit axiomatizations for them and show that they are not finitely axiomatizable. For each of these sets (of complex, real and [positive] rational numbers) a language, including the multiplication operation, is introduced in a way that it allows quantifier elimination (for the theory of that set).

9

Tinput-Driven Pushdown, Counter, and Stack Automata

Kutrib M., Malcher A., Wendlandt M.

Fundamenta Informaticae

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2017

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Vol. 155, nr 1/2

59--88

EN

In input-driven automata the input alphabet is divided into distinct classes and different actions on the storage medium are solely governed by the input symbols. For example, in inputdriven pushdown automata (IDPDA) there are three distinct classes of input symbols determining the action of pushing, popping, or doing nothing on the pushdown store. Here, input-driven automata are extended in such a way that the input is preprocessed by a deterministic sequential transducer. IDPDAs extended in this way are called tinput-driven pushdown automata (TDPDA) and it turns out that TDPDAs are more powerful than IDPDAs but still not as powerful as real-time deterministic pushdown automata. Nevertheless, even this stronger model has still good closure and decidability properties. In detail, it is shown that TDPDAs are closed under the Boolean operations union, intersection, and complementation. Furthermore, decidability procedures for the inclusion problem as well as for the questions of whether a given automaton is a TDPDA or an IDPDA are developed. Additionally, representation theorems for the context-free languages using IDPDAs and TDPDAs are established. Two other classes investigated are on the one hand TDPDAs restricted to tinput-driven counter automata and on the other hand TDPDAs generalized to tinput-driven stack automata. In both cases, it is possible to preserve the good closure and decidability properties of TDPDAs, namely, the closure under the Boolean operations as well as the decidability of the inclusion problem.

10

Soundness of Timed-Arc Workflow Nets in Discrete and Continuous-Time Semantics

Mateo J. A., Srba J., Sørensen M. G.

Fundamenta Informaticae

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2015

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Vol. 140, nr 1

89--121

EN

Analysis of workflow processes with quantitative aspects like timing is of interest in numerous time-critical applications. We suggest a workflow model based on timed-arc Petri nets and study the foundational problems of soundness and strong (time-bounded) soundness. We first consider the discrete-time semantics (integer delays) and explore the decidability of the soundness problems and show, among others, that soundness is decidable for monotonic workflow nets while reachability is undecidable. For general timed-arc workflow nets soundness and strong soundness become undecidable, though we can design efficient verification algorithms for the subclass of bounded nets. We also discuss the soundness problem in the continuous-time semantics (real-number delays) and show that for nets with nonstrict guards (where the reachability question coincides for both semantics) the soundness checking problem does not in general follow the approach for the discrete semantics and different zone-based techniques are needed for introducing its decidability in the bounded case. Finally, we demonstrate the usability of our theory on the case studies of a Brake System Control Unit used in aircraft certification, the MPEG2 encoding algorithm, and a blood transfusion workflow. The implementation of the algorithms is freely available as a part of the model checker TAPAAL (www.tapaal.net).

11

An analytical method for well-formed workflow/Petri net verification of classical soundness

Clempner J.

International Journal of Applied Mathematics and Computer Science

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2014

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Vol. 24, no. 4

931--939

EN

In this paper we consider workflow nets as dynamical systems governed by ordinary difference equations described by a particular class of Petri nets. Workflow nets are a formal model of business processes. Well-formed business processes correspond to sound workflow nets. Even if it seems necessary to require the soundness of workflow nets, there exist business processes with conditional behavior that will not necessarily satisfy the soundness property. In this sense, we propose an analytical method for showing that a workflow net satisfies the classical soundness property using a Petri net. To present our statement, we use Lyapunov stability theory to tackle the classical soundness verification problem for a class of dynamical systems described by Petri nets. This class of Petri nets allows a dynamical model representation that can be expressed in terms of difference equations. As a result, by applying Lyapunov theory, the classical soundness property for workflow nets is solved proving that the Petri net representation is stable. We show that a finite and non-blocking workflow net satisfies the sound property if and only if its corresponding PN is stable, i.e., given the incidence matrix A of the corresponding PN, there exists a Φ strictly positive m vector such that AΦ ≤ 0. The key contribution of the paper is the analytical method itself that satisfies part of the definition of the classical soundness requirements. The method is designed for practical applications, guarantees that anomalies can be detected without domain knowledge, and can be easily implemented into existing commercial systems that do not support the verification of workflows. The validity of the proposed method is successfully demonstrated by application examples.

12

Properties of Languages with Catenation and Shuffle

Kudlek M., Flick N. E.

Fundamenta Informaticae

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2014

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Vol. 129, nr 1/2

117--132

EN

We present structural properties of languages constructed with catenation and shuffle, comprising iteration lemmata and closure properties of the language classes, as well as decidability results that follow.

13

Stochastic Cellular Automata: Correlations : Decidability and Simulations

Arrighi P., Schabanel N., Theyssier G.

Fundamenta Informaticae

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2013

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Vol. 126, nr 2-3

121--156

EN

This paper introduces a simple formalism for dealing with deterministic, non-deterministic and stochastic cellular automata in an unified and composable manner. This formalism allows for local probabilistic correlations, a feature which is not present in usual definitions. We show that this feature allows for strictly more behaviors (for instance, number conserving stochastic cellular automata require these local probabilistic correlations). We also show that several problems which are deceptively simple in the usual definitions, become undecidable when we allow for local probabilistic correlations, even in dimension one. Armed with this formalism, we extend the notion of intrinsic simulation between deterministic cellular automata, to the non-deterministic and stochastic settings. Although the intrinsic simulation relation is shown to become undecidable in dimension two and higher, we provide explicit tools to prove or disprove the existence of such a simulation between any two given stochastic cellular automata. Those tools rely upon a characterization of equality of stochastic global maps, shown to be equivalent to the existence of a stochastic coupling between the random sources. We apply them to prove that there is no universal stochastic cellular automaton. Yet we provide stochastic cellular automata achieving optimal partial universality, as well as a universal non-deterministic cellular automaton.

14

On Completeness and Decidability of Phase Space Invertible Asynchronous Cellular Automata

Wacker S., Worsch T.

Fundamenta Informaticae

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2013

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Vol. 126, nr 2-3

157--181

EN

While for synchronous deterministic cellular automata there is an accepted definition of reversibility, this is not the case for asynchronous cellular automata. We first discuss a few possibilities and then investigate what we call phase space invertible asynchronous cellular automata. We will show that for each Turing machine there is a phase space invertible purely asynchronous cellular automaton simulating it and that it is decidable whether an arbitrary-dimensional purely and a one-dimensional fully asynchronous cellular automaton is phase space invertible.

15

From One-dimensional to Two-dimensional Cellular Automata

Dennunzio A.

Fundamenta Informaticae

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2012

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Vol. 115, nr 1

87-105

EN

We enlighten the differences between one-dimensional and two-dimensional cellular automata by considering both the dynamical and decidability aspects. We also show a canonical representation theorem for the slicing constructions, a tool allowing to give the 2D version of important 1D CA notions as closing and positive expansivity and lift 1D results to the 2D settings.

16

The Sequence Equivalence Problem for Marked DT0L Systems

Honkala J.

Fundamenta Informaticae

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2011

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Vol. 110, nr 1-4

175-182

EN

We study the DT0L sequence equivalence problem for marked morphisms. We show that to decide this problem it is enough to consider initial terms involving at most 2n morphisms where n is the cardinality of the underlying alphabet.

17

Decidability Problems in Petri Nets with Names and Replication

Rosa-Velardo F., Frutos-Escrig D. de

Fundamenta Informaticae

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2011

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Vol. 105, nr 3

291-317

EN

In this paper we study decidability of several extensions of P/T nets with name creation and/or replication. In particular, we study how to restrict the models of RN systems (P/T nets extended with replication, for which reachability is undecidable) and í-RN systems (RN extendedwith name creation, which are Turing-complete, so that coverability is undecidable), in order to obtain decidability of reachability and coverability, respectively. We prove that if we forbid synchronizations between the different components in a RN system, then reachability is still decidable. Similarly, if we forbid name communication between the different components in a &nuRN system, or restrict communication so that it is allowed only for a given finite set of names, we obtain decidability of coverability. Finally, we consider a polyadic version of ν-PN (P/T nets extended with name creation), that we call pν-PN, in which tokens are tuples of names. We prove that pν-PN are Turing complete, and discuss how the results obtained for ν-RN systems can be translated to them.

18

Accelerations for the Coverability Set of Petri Nets with Names

Rosa-Velardo F., Martos-Salgado M., Frutos-Escrig D. de

Fundamenta Informaticae

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2011

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Vol. 113, nr 3/4

313-341

EN

Pure names are identifiers with no relation between them, except equality and inequality. In previous works we have extended P/T nets with the capability of creating and managing pure names, obtaining -PNs and proved that they are strictly well structured (WSTS), so that coverability and boundedness are decidable. Here we use the framework recently developed by Finkel and Goubault-Larrecq for forward analysis for WSTS, in the case of -PNs, to compute the cover, that gives a good over approximation of the set of reachable markings. We prove that the least complete domain containing the set of markings is effectively representable. Moreover, we prove that in the completion we can compute least upper bounds of simple loops. Therefore, a forward Karp-Miller procedure that computes the cover is applicable. However, we prove that in general the cover is not computable, so that the procedure is non-terminating in general. As a corollary, we obtain the analogous result for Transfer Data nets and Data Nets. Finally, we show that a slight modification of the forward analysis yields decidability of a weak form of boundedness called width-boundedness, and identify a subclass of -PN that we call dw-bounded v-PN, for which the cover is computable.

19

Undecidability Results for Timed Automata with Silent Transitions

Bouyer P., Haddad S., Reynier P-A.

Fundamenta Informaticae

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2009

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Vol. 92, nr 1-2

1-25

EN

In this work, we study decision problems related to timed automata with silent transitions (TAε) which strictly extend the expressiveness of timed automata (TA). We first answer negatively a central question raised by the introduction of silent transitions: can we decide whether the language recognized by a TAε can be recognized by some TA? Then we establish in the framework of TAε some old open conjectures that O. Finkel has recently solved for TA. His proofs follow a generic scheme which relies on the fact that only a finite number of configurations can be reached by a TA while reading a timed word. This property does not hold for TAε , the proofs in the framework of TAε thus require more elaborated arguments. We establish undecidability of complementability, minimization of the number of clocks, and closure under shuffle. We also show these results in the framework of infinite timed languages.

20

Expressiveness of Petri Nets with Stopwatches. Discrete-time Part

Magnin M, Molinaro P., Roux O-H.

Fundamenta Informaticae

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2009

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Vol. 97, nr 1/2

139-176

EN

With this contribution, we aim to draw a comprehensive classification of Petri nets with stopwatches w.r.t. expressiveness and decidability issues. This topic is too ambitious to be summarized in a single paper. That is why we present our results in two different parts. In the first part of our work, we established new results regarding to both dense-time and discrete-time semantics. We now focus on the discrete-time specificities. We address the class of bounded Petri nets with stopwatches and reset arcs (rSwPNs), which is an extension of T-time Petri nets (TPNs) where time is associated with transitions. Stopwatches can be reset, stopped and started. We recall the formal dense-time and discrete-time semantics of these models in terms of Transition Systems. We study the expressiveness of rSwPNs and its subclasses w.r.t. (weak) bisimilarity (behavioral semantics). The main results are following: 1) Discrete-time bounded TPNs, discrete-time bounded rSwPNs and untimed Petri nets are equally expressive; 2) The resulting (final) classification of models is given by a set of relations explained in Fig. 7. While investigating expressiveness, we exhibit proofs that can be easily extended to the resolution of decidability issues. Among other results, we prove that, for bounded rSwPNs, the state and marking reachability problems - undecidable with dense-time semantics - are decidable when discrete-time is considered. Table 1 gives a synthesis of the main decidability results for these models. For the sake of simplicity, our results are explained on a model such that the stopwatches behaviors are expressed using inhibitor arcs. Our conclusions can however be easily extended to the general class of Stopwatch Petri nets.