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Documents authored by Ledent, Jérémy

Document
DOI: 10.4230/LIPIcs.CSL.2024.30
A Many-Sorted Epistemic Logic for Chromatic Hypergraphs

Authors: Éric Goubault, Roman Kniazev, and Jérémy Ledent

Published in: LIPIcs, Volume 288, 32nd EACSL Annual Conference on Computer Science Logic (CSL 2024)

Abstract
We propose a many-sorted modal logic for reasoning about knowledge in multi-agent systems. Our logic introduces a clear distinction between participating agents and the environment. This allows to express local properties of agents and global properties of worlds in a uniform way, as well as to talk about the presence or absence of agents in a world. The logic subsumes the standard epistemic logic and is a conservative extension of it. The semantics is given in chromatic hypergraphs, a generalization of chromatic simplicial complexes, which were recently used to model knowledge in distributed systems. We show that the logic is sound and complete with respect to the intended semantics. We also show a further connection of chromatic hypergraphs with neighborhood frames.
Cite as

Éric Goubault, Roman Kniazev, and Jérémy Ledent. A Many-Sorted Epistemic Logic for Chromatic Hypergraphs. In 32nd EACSL Annual Conference on Computer Science Logic (CSL 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 288, pp. 30:1-30:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{goubault_et_al:LIPIcs.CSL.2024.30,
  author =	{Goubault, \'{E}ric and Kniazev, Roman and Ledent, J\'{e}r\'{e}my},
  title =	{{A Many-Sorted Epistemic Logic for Chromatic Hypergraphs}},
  booktitle =	{32nd EACSL Annual Conference on Computer Science Logic (CSL 2024)},
  pages =	{30:1--30:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-310-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{288},
  editor =	{Murano, Aniello and Silva, Alexandra},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2024.30},
  URN =		{urn:nbn:de:0030-drops-196730},
  doi =		{10.4230/LIPIcs.CSL.2024.30},
  annote =	{Keywords: Modal logics, epistemic logics, multi-agent systems, hypergraphs}
}
Document
DOI: 10.4230/LIPIcs.STACS.2022.33
A Simplicial Model for KB4_n: Epistemic Logic with Agents That May Die

Authors: Éric Goubault, Jérémy Ledent, and Sergio Rajsbaum

Published in: LIPIcs, Volume 219, 39th International Symposium on Theoretical Aspects of Computer Science (STACS 2022)

Abstract
The standard semantics of multi-agent epistemic logic S5_n is based on Kripke models whose accessibility relations are reflexive, symmetric and transitive. This one dimensional structure contains implicit higher-dimensional information beyond pairwise interactions, that we formalized as pure simplicial models in a previous work in Information and Computation 2021 [Éric Goubault et al., 2021]. Here we extend the theory to encompass simplicial models that are not necessarily pure. The corresponding class of Kripke models are those where the accessibility relation is symmetric and transitive, but might not be reflexive. Such models correspond to the epistemic logic KB4_n. Impure simplicial models arise in situations where two possible worlds may not have the same set of agents. We illustrate it with distributed computing examples of synchronous systems where processes may crash.
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Éric Goubault, Jérémy Ledent, and Sergio Rajsbaum. A Simplicial Model for KB4_n: Epistemic Logic with Agents That May Die. In 39th International Symposium on Theoretical Aspects of Computer Science (STACS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 219, pp. 33:1-33:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{goubault_et_al:LIPIcs.STACS.2022.33,
  author =	{Goubault, \'{E}ric and Ledent, J\'{e}r\'{e}my and Rajsbaum, Sergio},
  title =	{{A Simplicial Model for KB4\underlinen: Epistemic Logic with Agents That May Die}},
  booktitle =	{39th International Symposium on Theoretical Aspects of Computer Science (STACS 2022)},
  pages =	{33:1--33:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-222-8},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{219},
  editor =	{Berenbrink, Petra and Monmege, Benjamin},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2022.33},
  URN =		{urn:nbn:de:0030-drops-158434},
  doi =		{10.4230/LIPIcs.STACS.2022.33},
  annote =	{Keywords: Epistemic logic, Simplicial complexes, Distributed computing}
}
Document
DOI: 10.4230/LIPIcs.DISC.2019.21
Wait-Free Solvability of Equality Negation Tasks

Authors: Éric Goubault, Marijana Lazić, Jérémy Ledent, and Sergio Rajsbaum

Published in: LIPIcs, Volume 146, 33rd International Symposium on Distributed Computing (DISC 2019)

Abstract
We introduce a family of tasks for n processes, as a generalization of the two process equality negation task of Lo and Hadzilacos (SICOMP 2000). Each process starts the computation with a private input value taken from a finite set of possible inputs. After communicating with the other processes using immediate snapshots, the process must decide on a binary output value, 0 or 1. The specification of the task is the following: in an execution, if the set of input values is large enough, the processes should agree on the same output; if the set of inputs is small enough, the processes should disagree; and in-between these two cases, any output is allowed. Formally, this specification depends on two threshold parameters k and l, with k<l, indicating when the cardinality of the set of inputs becomes "small" or "large", respectively. We study the solvability of this task depending on those two parameters. First, we show that the task is solvable whenever k+2 <= l. For the remaining cases (l = k+1), we use various combinatorial topology techniques to obtain two impossibility results: the task is unsolvable if either k <= n/2 or n-k is odd. The remaining cases are still open.
Cite as

Éric Goubault, Marijana Lazić, Jérémy Ledent, and Sergio Rajsbaum. Wait-Free Solvability of Equality Negation Tasks. In 33rd International Symposium on Distributed Computing (DISC 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 146, pp. 21:1-21:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{goubault_et_al:LIPIcs.DISC.2019.21,
  author =	{Goubault, \'{E}ric and Lazi\'{c}, Marijana and Ledent, J\'{e}r\'{e}my and Rajsbaum, Sergio},
  title =	{{Wait-Free Solvability of Equality Negation Tasks}},
  booktitle =	{33rd International Symposium on Distributed Computing (DISC 2019)},
  pages =	{21:1--21:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-126-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{146},
  editor =	{Suomela, Jukka},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2019.21},
  URN =		{urn:nbn:de:0030-drops-113288},
  doi =		{10.4230/LIPIcs.DISC.2019.21},
  annote =	{Keywords: Equality negation, distributed computability, combinatorial topology}
}
Document
DOI: 10.4230/LIPIcs.CONCUR.2019.34
A Sound Foundation for the Topological Approach to Task Solvability

Authors: Jérémy Ledent and Samuel Mimram

Published in: LIPIcs, Volume 140, 30th International Conference on Concurrency Theory (CONCUR 2019)

Abstract
The area of fault-tolerant distributed computability is concerned with the solvability of decision tasks in various computational models where the processes might crash. A very successful approach to prove impossibility results in this context is that of combinatorial topology, started by Herlihy and Shavit’s paper in 1999. They proved that, for wait-free protocols where the processes communicate through read/write registers, a task is solvable if and only if there exists some map between simplicial complexes satisfying some properties. This approach was then extended to many different contexts, where the processes have access to various synchronization and communication primitives. Usually, in those cases, the existence of a simplicial map from the protocol complex to the output complex is taken as the definition of what it means to solve a task. In particular, no proof is provided of the fact that this abstract topological definition agrees with a more concrete operational definition of task solvability. In this paper, we bridge this gap by proving a version of Herlihy and Shavit’s theorem that applies to any kind of object. First, we start with a very general way of specifying concurrent objects, and we define what it means to implement an object B in a computational model where the processes are allowed to communicate through shared objects A_1, ..., A_k. Then, we derive the notion of a decision task as a special case of concurrent object. Finally, we prove an analogue of Herlihy and Shavit’s theorem in this context. In particular, our version of the theorem subsumes all the uses of the combinatorial topology approach that we are aware of.
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Jérémy Ledent and Samuel Mimram. A Sound Foundation for the Topological Approach to Task Solvability. In 30th International Conference on Concurrency Theory (CONCUR 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 140, pp. 34:1-34:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{ledent_et_al:LIPIcs.CONCUR.2019.34,
  author =	{Ledent, J\'{e}r\'{e}my and Mimram, Samuel},
  title =	{{A Sound Foundation for the Topological Approach to Task Solvability}},
  booktitle =	{30th International Conference on Concurrency Theory (CONCUR 2019)},
  pages =	{34:1--34:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-121-4},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{140},
  editor =	{Fokkink, Wan and van Glabbeek, Rob},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2019.34},
  URN =		{urn:nbn:de:0030-drops-109365},
  doi =		{10.4230/LIPIcs.CONCUR.2019.34},
  annote =	{Keywords: Fault-tolerant protocols, Asynchronous computability, Combinatorial topology, Protocol complex, Distributed task}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2018.28
Concurrent Specifications Beyond Linearizability

Authors: Éric Goubault, Jérémy Ledent, and Samuel Mimram

Published in: LIPIcs, Volume 125, 22nd International Conference on Principles of Distributed Systems (OPODIS 2018)

Abstract
With the advent of parallel architectures, distributed programs are used intensively and the question of how to formally specify the behaviors expected from such programs becomes crucial. A very general way to specify concurrent objects is to simply give the set of all the execution traces that we consider correct for the object. In many cases, one is only interested in studying a subclass of these concurrent specifications, and more convenient tools such as linearizability can be used to describe them. In this paper, what we call a concurrent specification will be a set of execution traces that moreover satisfies a number of axioms. As we argue, these are actually the only concurrent specifications of interest: we prove that, in a reasonable computational model, every program satisfies all of our axioms. Restricting to this class of concurrent specifications allows us to formally relate our concurrent specifications with the ones obtained by linearizability, as well as its more recent variants (set- and interval-linearizability).
Cite as

Éric Goubault, Jérémy Ledent, and Samuel Mimram. Concurrent Specifications Beyond Linearizability. In 22nd International Conference on Principles of Distributed Systems (OPODIS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 125, pp. 28:1-28:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{goubault_et_al:LIPIcs.OPODIS.2018.28,
  author =	{Goubault, \'{E}ric and Ledent, J\'{e}r\'{e}my and Mimram, Samuel},
  title =	{{Concurrent Specifications Beyond Linearizability}},
  booktitle =	{22nd International Conference on Principles of Distributed Systems (OPODIS 2018)},
  pages =	{28:1--28:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-098-9},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{125},
  editor =	{Cao, Jiannong and Ellen, Faith and Rodrigues, Luis and Ferreira, Bernardo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2018.28},
  URN =		{urn:nbn:de:0030-drops-100888},
  doi =		{10.4230/LIPIcs.OPODIS.2018.28},
  annote =	{Keywords: concurrent specification, concurrent object, linearizability}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2018.50
Brief Announcement: On the Impossibility of Detecting Concurrency

Authors: Éric Goubault, Jérémy Ledent, and Samuel Mimram

Published in: LIPIcs, Volume 121, 32nd International Symposium on Distributed Computing (DISC 2018)

Abstract
We identify a general principle of distributed computing: one cannot force two processes running in parallel to see each other. This principle is formally stated in the context of asynchronous processes communicating through shared objects, using trace-based semantics. We prove that it holds in a reasonable computational model, and then study the class of concurrent specifications which satisfy this property. This allows us to derive a Galois connection theorem for different variants of linearizability.
Cite as

Éric Goubault, Jérémy Ledent, and Samuel Mimram. Brief Announcement: On the Impossibility of Detecting Concurrency. In 32nd International Symposium on Distributed Computing (DISC 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 121, pp. 50:1-50:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{goubault_et_al:LIPIcs.DISC.2018.50,
  author =	{Goubault, \'{E}ric and Ledent, J\'{e}r\'{e}my and Mimram, Samuel},
  title =	{{Brief Announcement: On the Impossibility of Detecting Concurrency}},
  booktitle =	{32nd International Symposium on Distributed Computing (DISC 2018)},
  pages =	{50:1--50:4},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-092-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{121},
  editor =	{Schmid, Ulrich and Widder, Josef},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2018.50},
  URN =		{urn:nbn:de:0030-drops-98392},
  doi =		{10.4230/LIPIcs.DISC.2018.50},
  annote =	{Keywords: concurrent specification, concurrent object, linearizability}
}
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