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Volume

LIPIcs, Volume 348

36th International Conference on Concurrency Theory (CONCUR 2025)

CONCUR 2025, August 26-29, 2025, Aarhus, Denmark

Editors: Patricia Bouyer and Jaco van de Pol

Document

Invited Talk

DOI: 10.4230/LIPIcs.CONCUR.2025.2

Towards Categorical Quantum Concurrency Theory (Invited Talk)

Authors: Chris Heunen

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

Quantum computing inherently has concurrent aspects. Even with only local operations, qubits can influence each other. This ability leads to genuinely new quantum communication protocols, but also raises even thornier questions of causality than in classical concurrent computing. Monoidal categories and their string diagrams form a convenient and popular language for quantum computing. After an introduction to quantum concurrency, I will discuss the framework of tensor topology, which aims to analyse the interaction of several agents in monoidal categories, using notions from sheaf theory and ordered locales.

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Chris Heunen. Towards Categorical Quantum Concurrency Theory (Invited Talk). In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, p. 2:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{heunen:LIPIcs.CONCUR.2025.2,
  author =	{Heunen, Chris},
  title =	{{Towards Categorical Quantum Concurrency Theory}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{2:1--2:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.2},
  URN =		{urn:nbn:de:0030-drops-239527},
  doi =		{10.4230/LIPIcs.CONCUR.2025.2},
  annote =	{Keywords: Quantum computing, causality, monoidal categories, tensor topology}
}

Document

Invited Talk

DOI: 10.4230/LIPIcs.CONCUR.2025.3

On-The-Fly Verification: Advancements in Dependency Graphs (Invited Talk)

Authors: Jiří Srba

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

Dependency graphs have emerged as a versatile and powerful formalism with wide-ranging applications in formal verification. In this extended abstract, we provide an overview of selected advancements in on-the-fly verification techniques based on dependency graphs, focusing on the recent developments, optimizations and generalizations of this generic verification framework.

Cite as

Jiří Srba. On-The-Fly Verification: Advancements in Dependency Graphs (Invited Talk). In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 3:1-3:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{srba:LIPIcs.CONCUR.2025.3,
  author =	{Srba, Ji\v{r}{\'\i}},
  title =	{{On-The-Fly Verification: Advancements in Dependency Graphs}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{3:1--3:5},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.3},
  URN =		{urn:nbn:de:0030-drops-239534},
  doi =		{10.4230/LIPIcs.CONCUR.2025.3},
  annote =	{Keywords: dependency graphs, Boolean equation systems, on-the-fly algorithms, fixed-point computation, applications}
}

Document

Invited Talk

DOI: 10.4230/LIPIcs.CONCUR.2025.1

Linear Temporal Logic with Standpoint Modalities (Invited Talk)

Authors: Christel Baier

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

Standpoint logics have been introduced in recent work by Alvarez et al. as a multi-modal logic to reason about the integrated knowledge of multiple agents that might have different, possibly contradicting views ("standpoints"). The essential new feature are modalities for expressing that a property is conceivable according to the view of an agent. The talk considers the model checking problem for a standpoint extension of classical linear temporal logic (LTL) with five semantics for the standpoint modalities. The semantics differ in the information an agent can extract from the history. Starting with a generic non-elementary model checking algorithm that is applicable to all five semantics, a more detailed complexity analysis leads to improved upper bounds for four of the semantics. In three cases, the model checking problem turns out to be PSPACE-complete, i.e., not harder than the model checking problem for classical LTL, which stands in contrast to the known EXPSPACE-completeness result for the satisfiability problem for standpoint LTL.

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Christel Baier. Linear Temporal Logic with Standpoint Modalities (Invited Talk). In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, p. 1:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{baier:LIPIcs.CONCUR.2025.1,
  author =	{Baier, Christel},
  title =	{{Linear Temporal Logic with Standpoint Modalities}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{1:1--1:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.1},
  URN =		{urn:nbn:de:0030-drops-239513},
  doi =		{10.4230/LIPIcs.CONCUR.2025.1},
  annote =	{Keywords: Linear Temporal Logic, LTL, standpoint logics, multi-modal logic, model checking}
}

Document

DOI: 10.4230/LIPIcs.CONCUR.2025.19

Time for Timed Monitorability

Authors: Thomas M. Grosen, Sean Kauffman, Kim G. Larsen, and Martin Zimmermann

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

Monitoring is an important part of the verification toolbox, in particular in situations where exhaustive verification using, e.g., model-checking is infeasible. The goal of online monitoring is to determine the satisfaction or violation of a specification during runtime, i.e., based on finite execution prefixes. However, not every specification is amenable to monitoring, e.g., properties for which no finite execution can witness satisfaction or violation. Monitorability is the question of whether a given specification is amenable to monitoring, and has been extensively studied in discrete time. Here, we study the monitorability problem for real-time properties expressed as Timed Automata. For specifications given by deterministic Timed Muller Automata, we prove decidability while we show that the problem is undecidable for specifications given by nondeterministic Timed Büchi automata. Furthermore, we refine monitorability to also determine bounds on the number of events as well as the time that must pass before monitoring the property may yield an informative verdict. We prove that for deterministic Timed Muller automata, such bounds can be effectively computed. In contrast we show that for nondeterministic Timed Büchi automata such bounds are not computable.

Cite as

Thomas M. Grosen, Sean Kauffman, Kim G. Larsen, and Martin Zimmermann. Time for Timed Monitorability. In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 19:1-19:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{grosen_et_al:LIPIcs.CONCUR.2025.19,
  author =	{Grosen, Thomas M. and Kauffman, Sean and Larsen, Kim G. and Zimmermann, Martin},
  title =	{{Time for Timed Monitorability}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{19:1--19:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.19},
  URN =		{urn:nbn:de:0030-drops-239690},
  doi =		{10.4230/LIPIcs.CONCUR.2025.19},
  annote =	{Keywords: Monitorability, Monitoring, Timed Automata, MITL}
}

Document

DOI: 10.4230/LIPIcs.CONCUR.2025.20

Compositional Active Learning of Synchronizing Systems Through Automated Alphabet Refinement

Authors: Léo Henry, Mohammad Reza Mousavi, Thomas Neele, and Matteo Sammartino

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

Active automata learning infers automaton models of systems from behavioral observations, a technique successfully applied to a wide range of domains. Compositional approaches for concurrent systems have recently emerged. We take a significant step beyond available results, including those by the authors, and develop a general technique for compositional learning of a synchronizing parallel system with an unknown decomposition. Our approach automatically refines the global alphabet into component alphabets while learning the component models. We develop a theoretical treatment of distributions of alphabets, i.e., sets of possibly overlapping component alphabets. We characterize counter-examples that reveal inconsistencies with global observations, and show how to systematically update the distribution to restore consistency. We present a compositional learning algorithm implementing these ideas, where learning counterexamples precisely correspond to distribution counterexamples under well-defined conditions. We provide an implementation, called CoalA, using the state-of-the-art active learning library LearnLib. Our experiments show that in more than 630 subject systems, CoalA delivers orders of magnitude improvements (up to five orders) in membership queries and in systems with significant concurrency, it also achieves better scalability in the number of equivalence queries.

Cite as

Léo Henry, Mohammad Reza Mousavi, Thomas Neele, and Matteo Sammartino. Compositional Active Learning of Synchronizing Systems Through Automated Alphabet Refinement. In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 20:1-20:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{henry_et_al:LIPIcs.CONCUR.2025.20,
  author =	{Henry, L\'{e}o and Mousavi, Mohammad Reza and Neele, Thomas and Sammartino, Matteo},
  title =	{{Compositional Active Learning of Synchronizing Systems Through Automated Alphabet Refinement}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{20:1--20:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.20},
  URN =		{urn:nbn:de:0030-drops-239700},
  doi =		{10.4230/LIPIcs.CONCUR.2025.20},
  annote =	{Keywords: Active learning, Compositional methods, Concurrency theory, Labelled transition systems, Formal methods}
}

Document

DOI: 10.4230/LIPIcs.CONCUR.2025.15

On the Send-Synchronizability Problem for Mailbox Communication

Authors: Romain Delpy, Anca Muscholl, and Grégoire Sutre

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

A system of communicating automata is send-synchronizable if its set of send sequences (i.e., the projection on send actions of its executions) is the same when communications are asynchronous and when they are rendez-vous synchronizations. Send-synchronizability was claimed to be decidable for the mailbox semantics (Basu and Bultan, 2011) and for the peer-to-peer semantics (Basu and Bultan, 2016). Finkel and Lozes showed in 2017 that the proofs of these results are flawed, and they proved that send-synchronizability is in fact undecidable for peer-to-peer systems. The send-synchronizability problem for mailbox systems was left open. A partial solution was recently proposed in (Di Giusto, Laversa and Peters, 2024). In this paper, we revisit the send-synchronizability problem for mailbox systems. Firstly, we show that send-synchronizability is undecidable for mailbox systems, thus closing the question left open in (Finkel and Lozes, 2023) and (Di Giusto, Laversa and Peters, 2024). Secondly, we show that send-synchronizability is decidable for the class of 1-schedulable mailbox systems. A system is 1-schedulable if every execution can be re-scheduled into an equivalent execution where each send is either immediately followed by its matching receive, or is never matched. Despite the apparent similarity between send-synchronizability and 1-schedulability, the proof that send-synchronizability is decidable for 1-schedulable mailbox systems is quite involved. We believe that the techniques that we develop in this proof could be used to address other problems on mailbox systems, such as the realizability problem.

Cite as

Romain Delpy, Anca Muscholl, and Grégoire Sutre. On the Send-Synchronizability Problem for Mailbox Communication. In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 15:1-15:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{delpy_et_al:LIPIcs.CONCUR.2025.15,
  author =	{Delpy, Romain and Muscholl, Anca and Sutre, Gr\'{e}goire},
  title =	{{On the Send-Synchronizability Problem for Mailbox Communication}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{15:1--15:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.15},
  URN =		{urn:nbn:de:0030-drops-239659},
  doi =		{10.4230/LIPIcs.CONCUR.2025.15},
  annote =	{Keywords: Concurrent programming, Mailbox communication, Verification, Synchronizability}
}

Document

DOI: 10.4230/LIPIcs.CONCUR.2025.16

Expectation in Stochastic Games with Prefix-Independent Objectives

Authors: Laurent Doyen, Pranshu Gaba, and Shibashis Guha

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

Stochastic two-player games model systems with an environment that is both adversarial and stochastic. In this paper, we study the expected value of bounded quantitative prefix-independent objectives in the context of stochastic games. We show a generic reduction from the expectation problem to linearly many instances of the almost-sure satisfaction problem for threshold Boolean objectives. The result follows from partitioning the vertices of the game into so-called value classes where each class consists of vertices of the same value. Our procedure further entails that the memory required by both players to play optimally for the expectation problem is no more than the memory required by the players to play optimally for the almost-sure satisfaction problem for a corresponding threshold Boolean objective. We show the applicability of the framework to compute the expected window mean-payoff measure in stochastic games. The window mean-payoff measure strengthens the classical mean-payoff measure by computing the mean payoff over windows of bounded length that slide along an infinite path. We show that the decision problem to check if the expected window mean-payoff value is at least a given threshold is in UP ∩ coUP when the window length is given in unary.

Cite as

Laurent Doyen, Pranshu Gaba, and Shibashis Guha. Expectation in Stochastic Games with Prefix-Independent Objectives. In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 16:1-16:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{doyen_et_al:LIPIcs.CONCUR.2025.16,
  author =	{Doyen, Laurent and Gaba, Pranshu and Guha, Shibashis},
  title =	{{Expectation in Stochastic Games with Prefix-Independent Objectives}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{16:1--16:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.16},
  URN =		{urn:nbn:de:0030-drops-239668},
  doi =		{10.4230/LIPIcs.CONCUR.2025.16},
  annote =	{Keywords: Stochastic games, finitary objectives, mean payoff, reactive synthesis}
}

Document

DOI: 10.4230/LIPIcs.CONCUR.2025.26

Optimal Concolic Dynamic Partial Order Reduction

Authors: Mohammad Hossein Khoshechin Jorshari, Michalis Kokologiannakis, Rupak Majumdar, and Srinidhi Nagendra

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

Stateless model checking (SMC) software implementations requires exploring both concurrency- and data nondeterminism. Unfortunately, most SMC algorithms focus on efficient exploration of concurrency nondeterminism, thereby neglecting an important source of bugs. We present ConDpor, an SMC algorithm for unmodified Java programs that combines optimal dynamic partial order reduction (DPOR) for concurrency nondeterminism, with concolic execution for data nondeterminism. ConDpor is sound, complete, optimal, and parametric w.r.t. the memory consistency model. Our experiments confirm that ConDpor is exponentially faster than DPOR with small-domain enumeration. Overall, ConDpor opens the door for efficient exploration of concurrent programs with data nondeterminism.

Cite as

Mohammad Hossein Khoshechin Jorshari, Michalis Kokologiannakis, Rupak Majumdar, and Srinidhi Nagendra. Optimal Concolic Dynamic Partial Order Reduction. In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 26:1-26:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{khoshechinjorshari_et_al:LIPIcs.CONCUR.2025.26,
  author =	{Khoshechin Jorshari, Mohammad Hossein and Kokologiannakis, Michalis and Majumdar, Rupak and Nagendra, Srinidhi},
  title =	{{Optimal Concolic Dynamic Partial Order Reduction}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{26:1--26:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.26},
  URN =		{urn:nbn:de:0030-drops-239765},
  doi =		{10.4230/LIPIcs.CONCUR.2025.26},
  annote =	{Keywords: Stateless model checking, dynamic symbolic execution}
}

Document

DOI: 10.4230/LIPIcs.CONCUR.2025.17

Just Verification of Mutual Exclusion Algorithms

Authors: Rob van Glabbeek, Bas Luttik, and Myrthe S. C. Spronck

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

We verify the correctness of a variety of mutual exclusion algorithms through model checking. We look at algorithms where communication is via shared read/write registers, where those registers can be atomic or non-atomic. For the verification of liveness properties, it is necessary to assume a completeness criterion to eliminate spurious counterexamples. We use justness as completeness criterion. Justness depends on a concurrency relation; we consider several such relations, modelling different assumptions on the working of the shared registers. We present executions demonstrating the violation of correctness properties by several algorithms, and in some cases suggest improvements.

Cite as

Rob van Glabbeek, Bas Luttik, and Myrthe S. C. Spronck. Just Verification of Mutual Exclusion Algorithms. In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 17:1-17:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{vanglabbeek_et_al:LIPIcs.CONCUR.2025.17,
  author =	{van Glabbeek, Rob and Luttik, Bas and Spronck, Myrthe S. C.},
  title =	{{Just Verification of Mutual Exclusion Algorithms}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{17:1--17:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.17},
  URN =		{urn:nbn:de:0030-drops-239670},
  doi =		{10.4230/LIPIcs.CONCUR.2025.17},
  annote =	{Keywords: Mutual exclusion, safe registers, regular registers, overlapping reads and writes, atomicity, safety, liveness, starvation freedom, justness, model checking, mCRL2}
}

Document

DOI: 10.4230/LIPIcs.CONCUR.2025.22

Partial-Order Reduction Is Hard

Authors: Frédéric Herbreteau, Sarah Larroze-Jardiné, and Igor Walukiewicz

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

The goal of partial-order methods is to accelerate the exploration of concurrent systems by examining only a representative subset of all possible runs. The stateful approach builds a transition system with representative runs, while the stateless method simply enumerates them. The stateless approach may be preferable if the transition system is tree-like; otherwise, the stateful method is more effective. In the last decade, optimality has been a guiding principle for developing stateless partial-order reduction algorithms, and without doubt contributed to big progress in the field. In this paper we ask if we can get a similar principle for the stateful approach. We show that in stateful exploration, a polynomially close to optimal partial-order algorithm cannot exist unless P=NP. The result holds even for acyclic programs with just await instructions. This lower bound result justifies systematic study of heuristics for stateful partial-order reduction. We propose a notion of IFS oracle as a useful abstraction. The oracle can be used to get a very simple optimal stateless algorithm, which can then be adapted to a non-optimal stateful algorithm. While in general the oracle problem is NP-hard, we show a simple case where it can be solved in linear time.

Cite as

Frédéric Herbreteau, Sarah Larroze-Jardiné, and Igor Walukiewicz. Partial-Order Reduction Is Hard. In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 22:1-22:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{herbreteau_et_al:LIPIcs.CONCUR.2025.22,
  author =	{Herbreteau, Fr\'{e}d\'{e}ric and Larroze-Jardin\'{e}, Sarah and Walukiewicz, Igor},
  title =	{{Partial-Order Reduction Is Hard}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{22:1--22:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.22},
  URN =		{urn:nbn:de:0030-drops-239727},
  doi =		{10.4230/LIPIcs.CONCUR.2025.22},
  annote =	{Keywords: Formal verification, Concurrent systems, Partial-order reduction, Complexity}
}

Document

DOI: 10.4230/LIPIcs.CONCUR.2025.21

Quantitative Language Automata

Authors: Thomas A. Henzinger, Pavol Kebis, Nicolas Mazzocchi, and N. Ege Saraç

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

A quantitative word automaton (QWA) defines a function from infinite words to values. For example, every infinite run of a limit-average QWA 𝒜 obtains a mean payoff, and every word w ∈ Σ^ω is assigned the maximal mean payoff obtained by nondeterministic runs of 𝒜 over w. We introduce quantitative language automata (QLAs) that define functions from language generators (i.e., implementations) to values, where a language generator can be nonprobabilistic, defining a set of infinite words, or probabilistic, defining a probability measure over infinite words. A QLA consists of a QWA and an aggregator function. For example, given a QWA 𝒜, the infimum aggregator maps each language L ⊆ Σ^ω to the greatest lower bound assigned by 𝒜 to any word in L. For boolean value sets, QWAs define boolean properties of traces, and QLAs define boolean properties of sets of traces, i.e., hyperproperties. For more general value sets, QLAs serve as a specification language for a generalization of hyperproperties, called quantitative hyperproperties. A nonprobabilistic (resp. probabilistic) quantitative hyperproperty assigns a value to each set (resp. distribution) G of traces, e.g., the minimal (resp. expected) average response time exhibited by the traces in G. We give several examples of quantitative hyperproperties and investigate three paradigmatic problems for QLAs: evaluation, nonemptiness, and universality. In the evaluation problem, given a QLA 𝔸 and an implementation G, we ask for the value that 𝔸 assigns to G. In the nonemptiness (resp. universality) problem, given a QLA 𝔸 and a value k, we ask whether 𝔸 assigns at least k to some (resp. every) language. We provide a comprehensive picture of decidability for these problems for QLAs with common aggregators as well as their restrictions to ω-regular languages and trace distributions generated by finite-state Markov chains.

Cite as

Thomas A. Henzinger, Pavol Kebis, Nicolas Mazzocchi, and N. Ege Saraç. Quantitative Language Automata. In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 21:1-21:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{henzinger_et_al:LIPIcs.CONCUR.2025.21,
  author =	{Henzinger, Thomas A. and Kebis, Pavol and Mazzocchi, Nicolas and Sara\c{c}, N. Ege},
  title =	{{Quantitative Language Automata}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{21:1--21:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.21},
  URN =		{urn:nbn:de:0030-drops-239718},
  doi =		{10.4230/LIPIcs.CONCUR.2025.21},
  annote =	{Keywords: Quantitative hyperproperties, quantitative automata, automata-based verification}
}

Document

DOI: 10.4230/LIPIcs.CONCUR.2025.30

Open Bisimilarity for the π-Calculus with Mismatch

Authors: Tiange Liu, Alwen Tiu, and Ross Horne

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

Open bisimilarity is an equivalence relation for the π-calculus that is also congruence, making it suitable to use in compositional reasoning for mobile processes and communication protocols. The original definition of open bisimilarity, due to Sangiorgi, does not account for the mismatch operator, that is crucial in modelling real-world protocols. When mismatch is present, the congruence property no longer holds for open bisimilarity. In a LICS 2018 paper, Horne et al. proposed an extension of open bisimilarity, using a history-indexed class of relations, to address this problem. That definition, however, turns out to be non-compositional as we shall demonstrate in this paper. This paper presents a new definition of open bisimilarity in the π-calculus that incorporates mismatch. This is achieved by augmenting the transition semantics of the π-calculus with an explicit assumption about name distinctions, and by requiring that open bisimulation to be closed under an arbitary extension of the name distinctions assumption. We then prove that the resulting open bisimilarity is both an equivalence relation and a congruence.

Cite as

Tiange Liu, Alwen Tiu, and Ross Horne. Open Bisimilarity for the π-Calculus with Mismatch. In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 30:1-30:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{liu_et_al:LIPIcs.CONCUR.2025.30,
  author =	{Liu, Tiange and Tiu, Alwen and Horne, Ross},
  title =	{{Open Bisimilarity for the \pi-Calculus with Mismatch}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{30:1--30:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.30},
  URN =		{urn:nbn:de:0030-drops-239805},
  doi =		{10.4230/LIPIcs.CONCUR.2025.30},
  annote =	{Keywords: mismatch, open bisimilarity, pi calculus}
}

Document

DOI: 10.4230/LIPIcs.CONCUR.2025.23

First-Order Store and Visibility in Name-Passing Calculi

Authors: Daniel Hirschkoff, Iwan Quémerais, and Davide Sangiorgi

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

The π-calculus is the paradigmatical name-passing calculus. While being purely name-passing, it allows the representation of higher-order functions and store. We study how π-calculus processes can be controlled so that computations can only involve storage of first-order values. The discipline is enforced by a type system that is based on the notion of visibility, coming from game semantics. We discuss the impact of visibility on the behavioural theory. We propose characterisations of may-testing and barbed equivalence, based on (variants of) trace equivalence and labelled bisimilarity, in the case where computation is sequential, and in the case where computation is well-bracketed.

Cite as

Daniel Hirschkoff, Iwan Quémerais, and Davide Sangiorgi. First-Order Store and Visibility in Name-Passing Calculi. In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 23:1-23:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{hirschkoff_et_al:LIPIcs.CONCUR.2025.23,
  author =	{Hirschkoff, Daniel and Qu\'{e}merais, Iwan and Sangiorgi, Davide},
  title =	{{First-Order Store and Visibility in Name-Passing Calculi}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{23:1--23:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.23},
  URN =		{urn:nbn:de:0030-drops-239737},
  doi =		{10.4230/LIPIcs.CONCUR.2025.23},
  annote =	{Keywords: process calculi, behavioural equivalence, type system}
}

Document

DOI: 10.4230/LIPIcs.CONCUR.2025.18

A State-Based O(m log n) Partitioning Algorithm for Branching Bisimilarity

Authors: Jan Friso Groote and David N. Jansen

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

We present a new O(mlog n) algorithm to calculate branching bisimulation equivalence, which is the finest commonly used behavioural equivalence on labelled transition systems that takes the internal action τ into account. This algorithm combines the simpler data structure of an earlier algorithm for Kripke structures (without action labels) with the memory-efficiency of a later algorithm partitioning sets of labelled transitions. It employs a particularly elegant four-way split of blocks of states, which refines a block under two splitters and isolates all new bottom states, simultaneously. Benchmark results show that this new algorithm outperforms the best known algorithm for branching bisimulation both in time and space.

Cite as

Jan Friso Groote and David N. Jansen. A State-Based O(m log n) Partitioning Algorithm for Branching Bisimilarity. In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 18:1-18:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{groote_et_al:LIPIcs.CONCUR.2025.18,
  author =	{Groote, Jan Friso and Jansen, David N.},
  title =	{{A State-Based O(m log n) Partitioning Algorithm for Branching Bisimilarity}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{18:1--18:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.18},
  URN =		{urn:nbn:de:0030-drops-239688},
  doi =		{10.4230/LIPIcs.CONCUR.2025.18},
  annote =	{Keywords: Algorithm, Branching bisimulation, Partition refinement of states}
}

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