34 Search Results for "Bertrand, Nathalie"

Document
DOI: 10.4230/LIPIcs.STACS.2026.31
Lower Bounds for Ranking-Based Pivot Rules

Authors: Yann Disser, Georg Loho, Matthew Maat, and Nils Mosis

Published in: LIPIcs, Volume 364, 43rd International Symposium on Theoretical Aspects of Computer Science (STACS 2026)

Abstract
The existence of a polynomial pivot rule for the simplex method for linear programming, policy iteration for Markov decision processes, and strategy improvement for parity games each are prominent open problems in their respective fields. While numerous natural candidates for efficient rules have been eliminated, all existing lower bound constructions are tailored to individual or small sets of pivot rules. We introduce a unified framework for formalizing classes of rules according to the information about the input that they rely on. Within this framework, we show lower bounds for ranking-based classes of rules that base their decisions on orderings of the improving pivot steps induced by the underlying data. Our first result is a superpolynomial lower bound for strategy improvement, obtained via a family of sink parity games, which applies to memory-based generalizations of Bland’s rule that only access the input by comparing the ranks of improving edges in some global order. Our second result is a subexponential lower bound for policy iteration, obtained via a family of Markov decision processes, which applies to memoryless rules that only access the input by comparing improving actions according to their ranks in a global order, their reduced costs, and the associated improvements in objective value. Both results carry over to the simplex method for linear programming.
Cite as

Yann Disser, Georg Loho, Matthew Maat, and Nils Mosis. Lower Bounds for Ranking-Based Pivot Rules. In 43rd International Symposium on Theoretical Aspects of Computer Science (STACS 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 364, pp. 31:1-31:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{disser_et_al:LIPIcs.STACS.2026.31,
  author =	{Disser, Yann and Loho, Georg and Maat, Matthew and Mosis, Nils},
  title =	{{Lower Bounds for Ranking-Based Pivot Rules}},
  booktitle =	{43rd International Symposium on Theoretical Aspects of Computer Science (STACS 2026)},
  pages =	{31:1--31:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-412-3},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{364},
  editor =	{Mahajan, Meena and Manea, Florin and McIver, Annabelle and Thắng, Nguy\~{ê}n Kim},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2026.31},
  URN =		{urn:nbn:de:0030-drops-255207},
  doi =		{10.4230/LIPIcs.STACS.2026.31},
  annote =	{Keywords: lower bounds, Markov decision processes, parity games, pivot rules, policy iteration, simplex method}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2025.8
Parameterized Verification of Timed Networks with Clock Invariants

Authors: Étienne André, Swen Jacobs, Shyam Lal Karra, and Ocan Sankur

Published in: LIPIcs, Volume 360, 45th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2025)

Abstract
We consider parameterized verification problems for networks of timed automata (TAs) based on different communication primitives. To this end, we first consider disjunctive timed networks (DTNs), i.e., networks of TAs that communicate via location guards that enable a transition only if there is another process in a certain location. We solve for the first time the case with unrestricted clock invariants, and establish that the parameterized model checking problem (PMCP) over finite local traces can be reduced to the corresponding model checking problem on a single TA. Moreover, we prove that the PMCP for networks that communicate via lossy broadcast can be reduced to the PMCP for DTNs. Finally, we show that for networks with k-wise synchronization, and therefore also for timed Petri nets, location reachability can be reduced to location reachability in DTNs. As a consequence we can answer positively the open problem from Abdulla et al. (2018) whether the universal safety problem for timed Petri nets with multiple clocks is decidable.
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Étienne André, Swen Jacobs, Shyam Lal Karra, and Ocan Sankur. Parameterized Verification of Timed Networks with Clock Invariants. In 45th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 360, pp. 8:1-8:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{andre_et_al:LIPIcs.FSTTCS.2025.8,
  author =	{Andr\'{e}, \'{E}tienne and Jacobs, Swen and Karra, Shyam Lal and Sankur, Ocan},
  title =	{{Parameterized Verification of Timed Networks with Clock Invariants}},
  booktitle =	{45th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2025)},
  pages =	{8:1--8:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-406-2},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{360},
  editor =	{Aiswarya, C. and Mehta, Ruta and Roy, Subhajit},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2025.8},
  URN =		{urn:nbn:de:0030-drops-250878},
  doi =		{10.4230/LIPIcs.FSTTCS.2025.8},
  annote =	{Keywords: Networks of Timed Automata, Parameterized Verification, Timed Petri Nets}
}
Document
DOI: 10.4230/OASIcs.SpaceCHI.2025.30
A Research Framework to Develop a Real-Time Synchrony Index to Monitor Team Cohesion and Performance in Long-Duration Space Exploration

Authors: Federico Nemmi, Emma Chabani, Laure Boyer, Charlie Madier, and Daniel Lewkowicz

Published in: OASIcs, Volume 130, Advancing Human-Computer Interaction for Space Exploration (SpaceCHI 2025)

Abstract
As humanity prepares for long-distance space exploration, optimizing group performance, the ability of a group to achieve its goals efficiently, is critical. Astronaut crews will endure isolation, confinement, and operational stress, making group synchrony - the alignment of behaviors, emotions, and physiological states - a key factor in mission success. Synchrony influences team cohesion, performance, and resilience, necessitating effective crew management strategies. This paper proposes a framework for a real-time, unobtrusive index of group synchrony to support astronauts and mission control. Research indicates that team cohesion fluctuates in isolated environments, with reduced communication and interpersonal conflicts emerging over time. A system tracking synchrony could mitigate these issues, providing proactive support and improving remote management. Additionally, it could serve as a cognitive and physiological feedback tool for astronauts and a decision-making aid for mission control, enhancing well-being and efficiency. Our approach integrates behavioral and physiological synchrony measures to assess team cohesion and performance. We propose a multi-modal synchrony index combining movement coordination, communication patterns, and physiological signals such as heart rate, electrodermal activity, and EEG. This index will be validated across different tasks to ensure applicability across diverse mission scenarios. By developing a robust synchrony index, we address a fundamental challenge in space missions: sustaining team effectiveness under extreme conditions. Beyond space exploration, our findings could benefit high-risk, high-isolation teams in submarine crews, polar expeditions, and remote research groups. Our collaboration with the Centre National d'Etudes Spatiales, the Institut de Médecine et de Physiologie Spatiales, and the Toulouse University Hospital marks the first step, with experimental data collection starting this year. Ultimately, this research fosters more adaptive, responsive, and resilient teams for future space missions.
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Federico Nemmi, Emma Chabani, Laure Boyer, Charlie Madier, and Daniel Lewkowicz. A Research Framework to Develop a Real-Time Synchrony Index to Monitor Team Cohesion and Performance in Long-Duration Space Exploration. In Advancing Human-Computer Interaction for Space Exploration (SpaceCHI 2025). Open Access Series in Informatics (OASIcs), Volume 130, pp. 30:1-30:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{nemmi_et_al:OASIcs.SpaceCHI.2025.30,
  author =	{Nemmi, Federico and Chabani, Emma and Boyer, Laure and Madier, Charlie and Lewkowicz, Daniel},
  title =	{{A Research Framework to Develop a Real-Time Synchrony Index to Monitor Team Cohesion and Performance in Long-Duration Space Exploration}},
  booktitle =	{Advancing Human-Computer Interaction for Space Exploration (SpaceCHI 2025)},
  pages =	{30:1--30:16},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-384-3},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{130},
  editor =	{Bensch, Leonie and Nilsson, Tommy and Nisser, Martin and Pataranutaporn, Pat and Schmidt, Albrecht and Sumini, Valentina},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.SpaceCHI.2025.30},
  URN =		{urn:nbn:de:0030-drops-240200},
  doi =		{10.4230/OASIcs.SpaceCHI.2025.30},
  annote =	{Keywords: Performance, Synchronie, Crew monitoring, Cohesion}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2025.31
Games with ω-Automatic Preference Relations

Authors: Véronique Bruyère, Christophe Grandmont, and Jean-François Raskin

Published in: LIPIcs, Volume 345, 50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025)

Abstract
This paper investigates Nash equilibria (NEs) in multi-player turn-based games on graphs, where player preferences are modeled as ω-automatic relations via deterministic parity automata. Unlike much of the existing literature, which focuses on specific reward functions, our results apply to any preference relation definable by an ω-automatic relation. We analyze the computational complexity of determining the existence of an NE (possibly under some constraints), verifying whether a given strategy profile forms an NE, and checking whether a specific outcome can be realized by an NE. When a (constrained) NE exists, we show that there always exists one with finite-memory strategies. Finally, we explore fundamental properties of ω-automatic relations and their implications in the existence of equilibria.
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Véronique Bruyère, Christophe Grandmont, and Jean-François Raskin. Games with ω-Automatic Preference Relations. In 50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 345, pp. 31:1-31:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{bruyere_et_al:LIPIcs.MFCS.2025.31,
  author =	{Bruy\`{e}re, V\'{e}ronique and Grandmont, Christophe and Raskin, Jean-Fran\c{c}ois},
  title =	{{Games with \omega-Automatic Preference Relations}},
  booktitle =	{50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025)},
  pages =	{31:1--31:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-388-1},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{345},
  editor =	{Gawrychowski, Pawe{\l} and Mazowiecki, Filip and Skrzypczak, Micha{\l}},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2025.31},
  URN =		{urn:nbn:de:0030-drops-241381},
  doi =		{10.4230/LIPIcs.MFCS.2025.31},
  annote =	{Keywords: Games played on graphs, Nash equilibrium, \omega-automatic relations, \omega-recognizable relations, constrained Nash equilibria existence problem}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2025.57
Resolving Nondeterminism with Randomness

Authors: Thomas A. Henzinger, Aditya Prakash, and K. S. Thejaswini

Published in: LIPIcs, Volume 345, 50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025)

Abstract
We define and study classes of ω-regular automata for which the nondeterminism can be resolved by a policy that uses a combination of memory and randomness on any input word, based solely on the prefix read so far. We examine two settings for providing the input word to an automaton. In the first setting, called adversarial resolvability, the input word is constructed letter-by-letter by an adversary, dependent on the resolver’s previous decisions. In the second setting, called stochastic resolvability, the adversary pre-commits to an infinite word and reveals it letter-by-letter. In each setting, we require the existence of an almost-sure resolver, i.e., a policy that ensures that as long as the adversary provides a word in the language of the underlying nondeterministic automaton, the run constructed by the policy is accepting with probability 1. The class of automata that are adversarially resolvable is the well-studied class of history-deterministic automata. The case of stochastically resolvable automata, on the other hand, defines a novel class. Restricting the class of resolvers in both settings to stochastic policies without memory introduces two additional new classes of automata. We show that the new automata classes offer interesting trade-offs between succinctness, expressivity, and computational complexity, providing a fine gradation between deterministic automata and nondeterministic automata.
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Thomas A. Henzinger, Aditya Prakash, and K. S. Thejaswini. Resolving Nondeterminism with Randomness. In 50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 345, pp. 57:1-57:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{henzinger_et_al:LIPIcs.MFCS.2025.57,
  author =	{Henzinger, Thomas A. and Prakash, Aditya and Thejaswini, K. S.},
  title =	{{Resolving Nondeterminism with Randomness}},
  booktitle =	{50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025)},
  pages =	{57:1--57:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-388-1},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{345},
  editor =	{Gawrychowski, Pawe{\l} and Mazowiecki, Filip and Skrzypczak, Micha{\l}},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2025.57},
  URN =		{urn:nbn:de:0030-drops-241645},
  doi =		{10.4230/LIPIcs.MFCS.2025.57},
  annote =	{Keywords: \omega-regular languages, History determinism, Stochastic strategies}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2025.66
Deciding Regular Games: a Playground for Exponential Time Algorithms

Authors: Zihui Liang, Bakh Khoussainov, and Mingyu Xiao

Published in: LIPIcs, Volume 345, 50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025)

Abstract
Regular games form a well-established class of games for analysis and synthesis of reactive systems. They include colored Muller games, McNaughton games, Muller games, Rabin games, and Streett games. These games are played on directed graphs G where Player 0 and Player 1 play by generating an infinite path ρ through the graph. The winner is determined by specifications put on the set X of vertices in ρ that occur infinitely often. These games are determined, enabling the partitioning of G into two sets Win₀ and Win₁ of winning positions for Player 0 and Player 1, respectively. Numerous algorithms exist that decide instances of regular games, e.g., Muller games, by computing Win₀ and Win₁. In this paper we aim to find general principles for designing uniform algorithms that decide all regular games. For this we utilize various recursive and dynamic programming algorithms that leverage standard notions such as subgames and traps. Importantly, we show that our techniques improve or match the performances of existing algorithms for many instances of regular games.
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Zihui Liang, Bakh Khoussainov, and Mingyu Xiao. Deciding Regular Games: a Playground for Exponential Time Algorithms. In 50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 345, pp. 66:1-66:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{liang_et_al:LIPIcs.MFCS.2025.66,
  author =	{Liang, Zihui and Khoussainov, Bakh and Xiao, Mingyu},
  title =	{{Deciding Regular Games: a Playground for Exponential Time Algorithms}},
  booktitle =	{50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025)},
  pages =	{66:1--66:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-388-1},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{345},
  editor =	{Gawrychowski, Pawe{\l} and Mazowiecki, Filip and Skrzypczak, Micha{\l}},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2025.66},
  URN =		{urn:nbn:de:0030-drops-241732},
  doi =		{10.4230/LIPIcs.MFCS.2025.66},
  annote =	{Keywords: Regular games, colored Muller games, Rabin games, McNaughton games, Muller games, deciding games}
}
Document
DOI: 10.4230/LIPIcs.CONCUR.2025.7
Temporal Explorability Games

Authors: Pete Austin, Sougata Bose, Nicolas Mazzocchi, and Patrick Totzke

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

Abstract
Temporal graphs extend ordinary graphs with discrete time that affects the availability of edges. We consider solving games played on temporal graphs where one player aims to explore the graph, i.e., visit all vertices. The complexity depends majorly on two factors: the presence of an adversary and how edge availability is specified. We demonstrate that on static graphs, where edges are always available, solving explorability games is just as hard as solving reachability games. In contrast, on temporal graphs, the complexity of explorability coincides with generalized reachability (NP-complete for one-player and PSPACE-complete for two player games). We show that if temporal graphs are given symbolically, even one-player reachability (and thus explorability and generalized reachability) games are PSPACE-hard. For one player, all these are also solvable in PSPACE and for two players, they are in PSPACE, EXP and EXP, respectively.
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Pete Austin, Sougata Bose, Nicolas Mazzocchi, and Patrick Totzke. Temporal Explorability Games. In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 7:1-7:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{austin_et_al:LIPIcs.CONCUR.2025.7,
  author =	{Austin, Pete and Bose, Sougata and Mazzocchi, Nicolas and Totzke, Patrick},
  title =	{{Temporal Explorability Games}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{7:1--7:17},
  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.2025.7},
  URN =		{urn:nbn:de:0030-drops-239575},
  doi =		{10.4230/LIPIcs.CONCUR.2025.7},
  annote =	{Keywords: Temporal Graphs, Explorability, Reachability, Games}
}
Document
Track B: Automata, Logic, Semantics, and Theory of Programming
DOI: 10.4230/LIPIcs.ICALP.2025.138
Taming Infinity One Chunk at a Time: Concisely Represented Strategies in One-Counter MDPs

Authors: Michal Ajdarów, James C. A. Main, Petr Novotný, and Mickael Randour

Published in: LIPIcs, Volume 334, 52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025)

Abstract
Markov decision processes (MDPs) are a canonical model to reason about decision making within a stochastic environment. We study a fundamental class of infinite MDPs: one-counter MDPs (OC-MDPs). They extend finite MDPs via an associated counter taking natural values, thus inducing an infinite MDP over the set of configurations (current state and counter value). We consider two characteristic objectives: reaching a target state (state-reachability), and reaching a target state with counter value zero (selective termination). The synthesis problem for the latter is not known to be decidable and connected to major open problems in number theory. Furthermore, even seemingly simple strategies (e.g., memoryless ones) in OC-MDPs might be impossible to build in practice (due to the underlying infinite configuration space): we need finite, and preferably small, representations. To overcome these obstacles, we introduce two natural classes of concisely represented strategies based on a (possibly infinite) partition of counter values in intervals. For both classes, and both objectives, we study the verification problem (does a given strategy ensure a high enough probability for the objective?), and two synthesis problems (does there exist such a strategy?): one where the interval partition is fixed as input, and one where it is only parameterized. We develop a generic approach based on a compression of the induced infinite MDP that yields decidability in all cases, with all complexities within PSPACE.
Cite as

Michal Ajdarów, James C. A. Main, Petr Novotný, and Mickael Randour. Taming Infinity One Chunk at a Time: Concisely Represented Strategies in One-Counter MDPs. In 52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 334, pp. 138:1-138:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{ajdarow_et_al:LIPIcs.ICALP.2025.138,
  author =	{Ajdar\'{o}w, Michal and Main, James C. A. and Novotn\'{y}, Petr and Randour, Mickael},
  title =	{{Taming Infinity One Chunk at a Time: Concisely Represented Strategies in One-Counter MDPs}},
  booktitle =	{52nd International Colloquium on Automata, Languages, and Programming (ICALP 2025)},
  pages =	{138:1--138:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-372-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{334},
  editor =	{Censor-Hillel, Keren and Grandoni, Fabrizio and Ouaknine, Jo\"{e}l and Puppis, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2025.138},
  URN =		{urn:nbn:de:0030-drops-235157},
  doi =		{10.4230/LIPIcs.ICALP.2025.138},
  annote =	{Keywords: one-counter Markov decision processes, randomised strategies, termination, reachability}
}
Document
DOI: 10.4230/OASIcs.FMBC.2025.8
Formal Verification of a Fail-Safe Cross-Chain Bridge

Authors: Filip Marić, Bernhard Scholz, and Pavle Subotić

Published in: OASIcs, Volume 129, 6th International Workshop on Formal Methods for Blockchains (FMBC 2025)

Abstract
Cross-chain bridges are financial services that interconnect blockchains. High monetary values flow through these bridges, and their security must be safeguarded. However, designing real-world cross-chain bridges is a difficult endeavor. Due to blockchain’s closed-world nature, tokens cannot be transferred from a sender to a receiver chain; on the contrary, they need complex logic that maintains an equilibrium on both chains, even if either the chains or the bridge fail. This paper formally verifies a model of a novel fail-safe cross-chain bridge to ensure correctness. We define formal requirements and prove the bridge is safe using the Isabelle/HOL proof assistant.
Cite as

Filip Marić, Bernhard Scholz, and Pavle Subotić. Formal Verification of a Fail-Safe Cross-Chain Bridge. In 6th International Workshop on Formal Methods for Blockchains (FMBC 2025). Open Access Series in Informatics (OASIcs), Volume 129, pp. 8:1-8:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{maric_et_al:OASIcs.FMBC.2025.8,
  author =	{Mari\'{c}, Filip and Scholz, Bernhard and Suboti\'{c}, Pavle},
  title =	{{Formal Verification of a Fail-Safe Cross-Chain Bridge}},
  booktitle =	{6th International Workshop on Formal Methods for Blockchains (FMBC 2025)},
  pages =	{8:1--8:18},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-371-3},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{129},
  editor =	{Marmsoler, Diego and Xu, Meng},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.FMBC.2025.8},
  URN =		{urn:nbn:de:0030-drops-230342},
  doi =		{10.4230/OASIcs.FMBC.2025.8},
  annote =	{Keywords: Cross-Chain Bridge, Formal Verification, Logic, Security}
}
Document
DOI: 10.4230/LIPIcs.STACS.2025.69
A Dichotomy Theorem for Ordinal Ranks in MSO

Authors: Damian Niwiński, Paweł Parys, and Michał Skrzypczak

Published in: LIPIcs, Volume 327, 42nd International Symposium on Theoretical Aspects of Computer Science (STACS 2025)

Abstract
We focus on formulae ∃X.φ(Y, X) of monadic second-order logic over the full binary tree, such that the witness X is a well-founded set. The ordinal rank rank(X) < ω₁ of such a set X measures its depth and branching structure. We search for the least upper bound for these ranks, and discover the following dichotomy depending on the formula φ. Let η_φ be the minimal ordinal such that, whenever an instance Y satisfies the formula, there is a witness X with rank(X) ≤ η_φ. Then η_φ is either strictly smaller than ω² or it reaches the maximal possible value ω₁. Moreover, it is decidable which of the cases holds. The result has potential for applications in a variety of ordinal-related problems, in particular it entails a result about the closure ordinal of a fixed-point formula.
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Damian Niwiński, Paweł Parys, and Michał Skrzypczak. A Dichotomy Theorem for Ordinal Ranks in MSO. In 42nd International Symposium on Theoretical Aspects of Computer Science (STACS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 327, pp. 69:1-69:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{niwinski_et_al:LIPIcs.STACS.2025.69,
  author =	{Niwi\'{n}ski, Damian and Parys, Pawe{\l} and Skrzypczak, Micha{\l}},
  title =	{{A Dichotomy Theorem for Ordinal Ranks in MSO}},
  booktitle =	{42nd International Symposium on Theoretical Aspects of Computer Science (STACS 2025)},
  pages =	{69:1--69:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-365-2},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{327},
  editor =	{Beyersdorff, Olaf and Pilipczuk, Micha{\l} and Pimentel, Elaine and Thắng, Nguy\~{ê}n Kim},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2025.69},
  URN =		{urn:nbn:de:0030-drops-228942},
  doi =		{10.4230/LIPIcs.STACS.2025.69},
  annote =	{Keywords: dichotomy result, limit ordinal, countable ordinals, nondeterministic tree automata}
}
Document
Invited Talk
DOI: 10.4230/LIPIcs.OPODIS.2023.1
From Consensus Research to Redbelly Network Pty Ltd (Invited Talk)

Authors: Vincent Gramoli

Published in: LIPIcs, Volume 286, 27th International Conference on Principles of Distributed Systems (OPODIS 2023)

Abstract
Designing and implementing correctly a blockchain system requires collaborations across places and research fields. Redbelly, a company across Australia, India and USA, illustrates well this idea. It started in 2005 at OPODIS, where we published the Reconfigurable Distributed Storage to replace distributed participants offering a service without disrupting its availability. This line of work [V. Gramoli et al., 2021] was instrumental to reconfigure blockchains without introducing hard forks. The research on the consensus problem we initiated at IRISA [V. Gramoli, 2022] led to rethinking PBFT-like algorithms for the context of blockchain by getting rid of the leader that can act as the bottleneck of large networks [V. Gramoli and Q. Tang, 2023]. Our work on security led to disclosing vulnerabilities in Ethereum [Parinya Ekparinya et al., 2020] and then motivated us to formally verify blockchain consensus [Nathalie Bertrand et al., 2022]. Our work at the frontier of economics [Michael Spain et al., 2019] led us to prevent front-running attacks [Pouriya Zarbafian and Vincent Gramoli, 2023] and to incentivize rational players to behave [Alejandro Ranchal-Pedrosa and Vincent Gramoli, 2022]. Our system work at Cornell and then at EPFL was foundational in experimenting blockchains across the globe [Vincent Gramoli et al., 2023]. Although not anticipated at the time, this series of work progressively led the University of Sydney and CSIRO, and later Redbelly Network Pty Ltd, to design the Redbelly Blockchain [Tyler Crain et al., 2021; Deepal Tennakoon et al., 2023], the platform of choice for compliant asset tokenisation.
Cite as

Vincent Gramoli. From Consensus Research to Redbelly Network Pty Ltd (Invited Talk). In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 1:1-1:2, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{gramoli:LIPIcs.OPODIS.2023.1,
  author =	{Gramoli, Vincent},
  title =	{{From Consensus Research to Redbelly Network Pty Ltd}},
  booktitle =	{27th International Conference on Principles of Distributed Systems (OPODIS 2023)},
  pages =	{1:1--1:2},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-308-9},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{286},
  editor =	{Bessani, Alysson and D\'{e}fago, Xavier and Nakamura, Junya and Wada, Koichi and Yamauchi, Yukiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2023.1},
  URN =		{urn:nbn:de:0030-drops-194915},
  doi =		{10.4230/LIPIcs.OPODIS.2023.1},
  annote =	{Keywords: Innovations, Commercialisation}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2023.88
Checking Presence Reachability Properties on Parameterized Shared-Memory Systems

Authors: Nicolas Waldburger

Published in: LIPIcs, Volume 272, 48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023)

Abstract
We consider the verification of distributed systems composed of an arbitrary number of asynchronous processes. Processes are identical finite-state machines that communicate by reading from and writing to a shared memory. Beyond the standard model with finitely many registers, we tackle round-based shared-memory systems with fresh registers at each round. In the latter model, both the number of processes and the number of registers are unbounded, making verification particularly challenging. The properties studied are generic presence reachability objectives, which subsume classical questions such as safety or synchronization by expressing the presence or absence of processes in some states. In the more general round-based setting, we establish that the parameterized verification of presence reachability properties is PSPACE-complete. Moreover, for the roundless model with finitely many registers, we prove that the complexity drops down to NP-complete and we provide several natural restrictions that make the problem solvable in polynomial time.
Cite as

Nicolas Waldburger. Checking Presence Reachability Properties on Parameterized Shared-Memory Systems. In 48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 272, pp. 88:1-88:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{waldburger:LIPIcs.MFCS.2023.88,
  author =	{Waldburger, Nicolas},
  title =	{{Checking Presence Reachability Properties on Parameterized Shared-Memory Systems}},
  booktitle =	{48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023)},
  pages =	{88:1--88:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-292-1},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{272},
  editor =	{Leroux, J\'{e}r\^{o}me and Lombardy, Sylvain and Peleg, David},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2023.88},
  URN =		{urn:nbn:de:0030-drops-186225},
  doi =		{10.4230/LIPIcs.MFCS.2023.88},
  annote =	{Keywords: Verification, Parameterized models, Distributed algorithms}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2022.32
Semilinear Representations for Series-Parallel Atomic Congestion Games

Authors: Nathalie Bertrand, Nicolas Markey, Suman Sadhukhan, and Ocan Sankur

Published in: LIPIcs, Volume 250, 42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2022)

Abstract
We consider atomic congestion games on series-parallel networks, and study the structure of the sets of Nash equilibria and social local optima on a given network when the number of players varies. We establish that these sets are definable in Presburger arithmetic and that they admit semilinear representations whose all period vectors have a common direction. As an application, we prove that the prices of anarchy and stability converge to 1 as the number of players goes to infinity, and show how to exploit these semilinear representations to compute these ratios precisely for a given network and number of players.
Cite as

Nathalie Bertrand, Nicolas Markey, Suman Sadhukhan, and Ocan Sankur. Semilinear Representations for Series-Parallel Atomic Congestion Games. In 42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 250, pp. 32:1-32:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bertrand_et_al:LIPIcs.FSTTCS.2022.32,
  author =	{Bertrand, Nathalie and Markey, Nicolas and Sadhukhan, Suman and Sankur, Ocan},
  title =	{{Semilinear Representations for Series-Parallel Atomic Congestion Games}},
  booktitle =	{42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2022)},
  pages =	{32:1--32:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-261-7},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{250},
  editor =	{Dawar, Anuj and Guruswami, Venkatesan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2022.32},
  URN =		{urn:nbn:de:0030-drops-174243},
  doi =		{10.4230/LIPIcs.FSTTCS.2022.32},
  annote =	{Keywords: congestion games, Nash equilibria, Presburger arithmetic, semilinear sets, price of anarchy}
}
Document
DOI: 10.4230/LIPIcs.DISC.2022.10
Holistic Verification of Blockchain Consensus

Authors: Nathalie Bertrand, Vincent Gramoli, Igor Konnov, Marijana Lazić, Pierre Tholoniat, and Josef Widder

Published in: LIPIcs, Volume 246, 36th International Symposium on Distributed Computing (DISC 2022)

Abstract
Blockchain has recently attracted the attention of the industry due, in part, to its ability to automate asset transfers. It requires distributed participants to reach a consensus on a block despite the presence of malicious (a.k.a. Byzantine) participants. Malicious participants exploit regularly weaknesses of these blockchain consensus algorithms, with sometimes devastating consequences. In fact, these weaknesses are quite common and are well illustrated by the flaws in various blockchain consensus algorithms [Pierre Tholoniat and Vincent Gramoli, 2019]. Paradoxically, until now, no blockchain consensus has been holistically verified. In this paper, we remedy this paradox by model checking for the first time a blockchain consensus used in industry. We propose a holistic approach to verify the consensus algorithm of the Red Belly Blockchain [Tyler Crain et al., 2021], for any number n of processes and any number f < n/3 of Byzantine processes. We decompose directly the algorithm pseudocode in two parts - an inner broadcast algorithm and an outer decision algorithm - each modelled as a threshold automaton [Igor Konnov et al., 2017], and we formalize their expected properties in linear-time temporal logic. We then automatically check the inner broadcasting algorithm, under a carefully identified fairness assumption. For the verification of the outer algorithm, we simplify the model of the inner algorithm by relying on its proven properties. Doing so, we formally verify, for any parameter, not only the safety properties of the Red Belly Blockchain consensus but also its liveness in less than 70 seconds.
Cite as

Nathalie Bertrand, Vincent Gramoli, Igor Konnov, Marijana Lazić, Pierre Tholoniat, and Josef Widder. Holistic Verification of Blockchain Consensus. In 36th International Symposium on Distributed Computing (DISC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 246, pp. 10:1-10:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bertrand_et_al:LIPIcs.DISC.2022.10,
  author =	{Bertrand, Nathalie and Gramoli, Vincent and Konnov, Igor and Lazi\'{c}, Marijana and Tholoniat, Pierre and Widder, Josef},
  title =	{{Holistic Verification of Blockchain Consensus}},
  booktitle =	{36th International Symposium on Distributed Computing (DISC 2022)},
  pages =	{10:1--10:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-255-6},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{246},
  editor =	{Scheideler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2022.10},
  URN =		{urn:nbn:de:0030-drops-172019},
  doi =		{10.4230/LIPIcs.DISC.2022.10},
  annote =	{Keywords: Model checking, automata, logic, byzantine failure}
}
Document
Track B: Automata, Logic, Semantics, and Theory of Programming
DOI: 10.4230/LIPIcs.ICALP.2022.113
Parameterized Safety Verification of Round-Based Shared-Memory Systems

Authors: Nathalie Bertrand, Nicolas Markey, Ocan Sankur, and Nicolas Waldburger

Published in: LIPIcs, Volume 229, 49th International Colloquium on Automata, Languages, and Programming (ICALP 2022)

Abstract
We consider the parameterized verification problem for distributed algorithms where the goal is to develop techniques to prove the correctness of a given algorithm regardless of the number of participating processes. Motivated by an asynchronous binary consensus algorithm [James Aspnes, 2002], we consider round-based distributed algorithms communicating with shared memory. A particular challenge in these systems is that 1) the number of processes is unbounded, and, more importantly, 2) there is a fresh set of registers at each round. A verification algorithm thus needs to manage both sources of infinity. In this setting, we prove that the safety verification problem, which consists in deciding whether all possible executions avoid a given error state, is PSPACE-complete. For negative instances of the safety verification problem, we also provide exponential lower and upper bounds on the minimal number of processes needed for an error execution and on the minimal round on which the error state can be covered.
Cite as

Nathalie Bertrand, Nicolas Markey, Ocan Sankur, and Nicolas Waldburger. Parameterized Safety Verification of Round-Based Shared-Memory Systems. In 49th International Colloquium on Automata, Languages, and Programming (ICALP 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 229, pp. 113:1-113:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bertrand_et_al:LIPIcs.ICALP.2022.113,
  author =	{Bertrand, Nathalie and Markey, Nicolas and Sankur, Ocan and Waldburger, Nicolas},
  title =	{{Parameterized Safety Verification of Round-Based Shared-Memory Systems}},
  booktitle =	{49th International Colloquium on Automata, Languages, and Programming (ICALP 2022)},
  pages =	{113:1--113:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-235-8},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{229},
  editor =	{Boja\'{n}czyk, Miko{\l}aj and Merelli, Emanuela and Woodruff, David P.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2022.113},
  URN =		{urn:nbn:de:0030-drops-164541},
  doi =		{10.4230/LIPIcs.ICALP.2022.113},
  annote =	{Keywords: Verification, Parameterized models, Distributed algorithms}
}
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