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Concurrency Theory

The 14th IFIP WG 1.8 Workshop on Trends in Concurrency Theory

September 5, 2026, Liverpool, UK

A satellite event of CONFEST 2026

Description

TRENDS 2026 is an event organised by IFIP WG 1.8 on Concurrency Theory. It aims at bringing together researchers interested in Concurrency Theory and its applications, to exchange ideas and discuss recent trends and open problems. The event will take place on September 5, 2026.

Invited Speakers

  • Rob van Glabbeek, University of Edinburgh, UK

    Title: Ensuring Liveness Properties of Distributed Systems with Justness

    A liveness property of a distributed system says that something good will eventually happen—typically that some desired goal state will be reached. Like all linear time properties, a liveness property holds for a system iff it holds for all its valid runs. In a system model such as labelled transition systems, a valid run of a real system is modelled by a complete path. We need a completeness criterion such as progress, justness or fairness to tell which paths are complete, and thus represent valid runs. These criteria can be seen as assumptions ones makes on system behaviour. When not making any such assumptions, no meaningful liveness property will ever be ensured.

    Progress says that a system will not stop midway its execution without a valid reason. It is too weak an assumption to ensure many crucial liveness properties of distributed systems. Fairness says that if one tries something often enough, it will eventually succeed. While strong enough for the verification of crucial liveness properties, it is actually too strong, and can lead to unwarranted conclusions. Fairness can be seen as a form of wishful thinking. For this reason I proposed, at TRENDS 2017, to base the verification of liveness properties of distributed systems on the assumption of justness, which forms a gulden middle ground between progress and fairness. Sadly, most of pre-2017 concurrency theory may need to be overhauled, as it is not compatible with justness. As an illustration, I gave you two strongly bisimilar systems of which one has a liveness property under the assumption of justness, whether the other does not.

    In this talk I describe some further developments of this idea in the last 9 years:

    • Just testing complements may- and must-testing, should-testing and reward testing as a 5th way to determine a suitable semantic equivalence and preorder—one that makes as few distinctions as possible, while being compatible with justness.
    • Enabling-preserving bisimilarity is a canonical refinement of strong bisimilarity that does justice to justness and allows for local reasoning in proving processes equivalent.
    • We found an extension of the De Simone format that ensures enabling-preserving bisimilarity to be a congruence, even for recursion.
    • When merely assuming justness instead of fairness, certain version of the classical mutual exclusion protocol become unsolvable. This holds in particular for the mutual exclusion problem as formulated by Dijkstra, and that gave rise to many dozens of papers proposing solutions.
    • On a certain class of models, justness could be formalised in the model mu-calculus. Using this, we employed mCRL2 to automatically verify though model checking more than a dozen mutual exclusion protocols under 4 different assumptions on how shared registers really work.

  • Tatjana Petrov, University of Trieste, IT & University of Konstanz, DE

    Title: From Individual Interactions to Collective Dynamics — and Back: Why Timing Matters

    Collective systems—from biochemical regulatory networks to animal groups, robotic swarms, and artificial multi-agent systems—are fascinating because relatively simple, local interaction rules can give rise to rich, robust, and adaptive collective behaviour. Understanding how microscopic interaction mechanisms shape collective dynamics can reveal design principles in natural systems and guide the construction of engineered ones. Conversely, collective observations may provide clues about the individual mechanisms that generated them. This gives rise to two complementary problems: how can we predict collective dynamics from microscopic interactions, and how much can we infer about individual mechanisms from partial observations of the collective?

    I will discuss these questions through stochastic population models of interacting agents. First, with examples inspired by gene regulation, I will illustrate how finite-size effects and multiple time scales can produce unexpected transient dynamics. I will then discuss formal and computational approaches for analysing and quantifying such behaviour, drawing on recent results on consensus robustness in stochastic swarms. On the inference side, I will consider how (sparse) observations of collective behaviour can be used to identify plausible models of individual interactions, drawing on our recent result on honeybee collective decision-making.

    I will conclude with open questions on scalable prediction, inference, and robustness in stochastic interacting systems, and on how these challenges extend to increasingly adaptive and strategic artificial multi-agent systems

  • Henning Urbat, FAU Erlangen-Nürnberg, DE

    Title: Abstract Operational Reasoning

    One of the key desiderata on any well-behaved process or programming language is its compositionality: if a component of a process or program is replaced with a behaviourally equivalent one, then the behaviour in the whole should remain unaffected. Standardly, each type of language (e.g. concurrent, probabilistic, stateful, higher-order) and each notion of behavioural equivalence (e.g. trace equivalence, weak or strong bisimilarity, or quantitative variations thereof) requires its own complex reasoning methods for establishing compositionality properties, which are developed ad hoc.

    In this talk, I give an overview of recent developments towards a uniform, language-independent approach to compositionality. It builds on various abstractions from category theory, specifically the idea to capture the operational semantics of a given language via a dinatural transformation that distributes the syntax of the langage over its behaviour type, with notions of behavioural equivalence corresponding to suitable choices of fibrations. Fundamental reasoning methods for compositionality, such as Howe’s method or logical relations, emerge at this level of generality and instantiate to a wide variety of different settings.

  • Jos Baeten, CWI, NL

    Book presentation: Models of Computation based on Automata: Formal Languages and Communicating Processes

    First-year students in computer science and related fields usually follow a course on Automata Theory and Formal Languages. This course gives students the foundations of computer science, and tells them what a computer can and cannot do. The course is usually based on the computer model called the Turing Machine, which adequately describes a computer as they were in the seventies: a stand-alone machine executing batch processes. However, the Turing machine is blind, deaf and dumb, very different from computers as we know them today. I would not let a Turing machine drive my car. This book integrates automata theory with process theory, and treats, alongside the classical results on correspondences between types of automata and grammars, their generalisations to a setting that facilitates communication and interaction, and moreover contains some new results. In just 200 pages with plenty of exercises, it can serve as a replacement of the classical course for first-year students.

Programme

8:30-9:00. Registration & Coffee

9:00-10:00. Rob van Glabbeek. “Ensuring Liveness Properties of Distributed Systems with Justness”

10:00-10:30. Coffee Break

10:30-11:30. Tatjana Petrov. “From Individual Interactions to Collective Dynamics — and Back: Why Timing Matters”

11:30-12:00. Jos Baeten. Book presentation: “Models of Computation based on Automata: Formal Languages and Communicating Processes”

12:00-13:30. Lunch Break

13:30-14:30. Henning Urbat. “Abstract Operational Reasoning”

14:30-15:00. Coffee Break

15:00-16:00. IFIP WG 1.8 Business meeting

Participation

Participation, both to the workshop and to the IFIP WG 1.8 meeting, is open to everybody. For registration, please consult the CONFEST 2026 home page.

Organizers

Pedro R. D’Argenio (Universidad Nacional de Córdoba, Argentina)

Ana Sokolova (University of Salzburg, Austria)

IFIP WG 1.8 on Concurrency Theory

The aims of IFIP WG 1.8 on Concurrency Theory are:

  • To develop theoretical foundations of concurrency, exploring frontiers of existing theoretical models like process algebra and process calculi, so as to obtain a deeper theoretical understanding of concurrent and parallel systems.

  • To promote and coordinate the exchange of information on concurrency theory, by sharing ideas, discussing open problems, and identifying future directions of research in the area.

The activities of this WG encompass all aspects of concurrency theory and its applications.

More information on IFIP WG 1.8 can be found on its home page.

History

The first instalment of TRENDS (TRENDS 2012) was held on September 8, 2012 as a satellite event of CONCUR 2012, in Newcastle upon Tyne, UK.

The second instalment of TRENDS (TRENDS 2013) was held on August 31, 2013 as a satellite event of CONCUR 2013, in Buenos Aires, Argentina.

The third instalment of TRENDS (TRENDS 2014) was held on September 6, 2014 as a satellite event of CONCUR 2014, in Rome, Italy.

The fourth instalment of TRENDS (TRENDS 2015) was held on September 6, 2015 as a satellite event of CONCUR 2015, in Madrid, Spain.

The fifth instalment of TRENDS (TRENDS 2016) was held on August 27, 2016 as a satellite event of CONCUR 2016, in Quebec City, Canada.

The sixth instalment of TRENDS (TRENDS 2017) was held on September 9, 2017 as a satellite event of CONCUR 2017, in Berlin, Germany.

The seventh instalment of TRENDS (TRENDS 2018) was held on September 8, 2018 as a satellite event of CONCUR 2018, in Beijing, China.

The eighth instalment of TRENDS (TRENDS 2019) was held on August 31, 2019 as a satellite event of CONCUR 2019, in Amsterdam, The Netherlands.

The ninth instalment of TRENDS (TRENDS 2020) was held on September 5, 2020 as a satellite event of CONCUR 2020, in Vienna, Austria Online.

The tenth instalment of TRENDS (TRENDS 2021) was held on August 28, 2021 as a satellite event of CONCUR 2021, in Paris, France Online.

The eleventh instalment of TRENDS (TRENDS 2022) was held on September 12, 2022 as a satellite event of CONCUR 2022, in Warsaw, Poland.

The twelveth instalment of TRENDS (TRENDS 2023) was held on September 23, 2023 as a satellite event of CONCUR 2023, in Antwerp, Belgium.

The thirteenth instalment of TRENDS (TRENDS 2024) was held on September 9, 2024 as a satellite event of CONCUR 2024, in Calgary, Canada.