20 Search Results for "Lafourcade, Pascal"

Document
DOI: 10.4230/LIPIcs.FUN.2026.10
77 Shades of Grey

Authors: Quentin Bramas, Stéphane Devismes, Anaïs Durand, Pascal Lafourcade, and Anissa Lamani

Published in: LIPIcs, Volume 366, 13th International Conference on Fun with Algorithms (FUN 2026)

Abstract
Bruce Wayne contacted us to help him develop a new surveillance technology for dark environments such as caves, using a swarm of Unmanned Aerial Vehicles (UAVs), called Batdroids. A Batdroid has no chirality, limited visibility, and a perfect clock to synchronize with the others. A Batdroid can produce 77 shades of grey in dark mode and four colors in light mode. In this paper, we propose two algorithms using three Batdroids to perpetually explore a finite 3D grid modeling a cave. The first algorithm operates in darkness, uses 77 shades of grey, and requires visibility range one. The second operates in light, uses four colors and visibility range two. We also prove that three is the optimal number of Batdroids required to solve Bruce Wayne’s challenge.
Cite as

Quentin Bramas, Stéphane Devismes, Anaïs Durand, Pascal Lafourcade, and Anissa Lamani. 77 Shades of Grey. In 13th International Conference on Fun with Algorithms (FUN 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 366, pp. 10:1-10:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{bramas_et_al:LIPIcs.FUN.2026.10,
  author =	{Bramas, Quentin and Devismes, St\'{e}phane and Durand, Ana\"{i}s and Lafourcade, Pascal and Lamani, Anissa},
  title =	{{77 Shades of Grey}},
  booktitle =	{13th International Conference on Fun with Algorithms (FUN 2026)},
  pages =	{10:1--10:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-417-8},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{366},
  editor =	{Iacono, John},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2026.10},
  URN =		{urn:nbn:de:0030-drops-257294},
  doi =		{10.4230/LIPIcs.FUN.2026.10},
  annote =	{Keywords: Mobile robots, grid exploration, perpetual exploration}
}
Document
DOI: 10.4230/LIPIcs.FUN.2026.16
Lozenge Tiling by Computing Distances

Authors: Jean-Marie Favreau, Yan Gerard, Pascal Lafourcade, and Léo Robert

Published in: LIPIcs, Volume 366, 13th International Conference on Fun with Algorithms (FUN 2026)

Abstract
The Calisson puzzle is a recent tiling game in which one must tile a triangular grid inside a hexagon with lozenges, under the constraint that certain prescribed edges must remain tile boundaries and that adjacent lozenges along these edges have different orientations. We present the first polynomial-time algorithm for this problem, with running time O(n³) for a hexagon of side length n. This algorithm, called the advancing surface algorithm, can be executed in a simple and intuitive way, even by hand with a pencil and an eraser. Its apparent simplicity conceals a deeper algorithmic reinterpretation of the classical ideas of John Conway and William Thurston, which we revisit from a theoretical computer science perspective. We introduce a graph-theoretic and difference constraints overlay that complements Thurston’s theory of lozenge tilings, revealing its intrinsic algorithmic structure and extending its scope to tiling problems with interior constraints and without necessarily boundary conditions. In Thurston’s approach, lozenge tilings are lifted to monotone stepped surfaces in the three-dimensional cubic lattice and projected back to the plane using height functions, reducing the tiling problem to the computation of heights. We show that, at an algorithmic level, selecting a monotone surface corresponds to selecting a directed cut (dicut) in a periodic directed graph, while height functions are solutions of a system of difference constraints. In this formulation, a region is tilable if and only if the associated weighted directed graph contains no cycle of strictly negative total weight. This new graph layer completing Thurston’s theory shows that Bellman–Ford’s shortest path algorithm is the only algorithmic primitive needed to decide feasibility and compute solutions. In particular, our framework allows us to decide whether the infinite triangular grid can be tiled while respecting a finite set of prescribed local constraints, a setting in which no boundary conditions are available.
Cite as

Jean-Marie Favreau, Yan Gerard, Pascal Lafourcade, and Léo Robert. Lozenge Tiling by Computing Distances. In 13th International Conference on Fun with Algorithms (FUN 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 366, pp. 16:1-16:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{favreau_et_al:LIPIcs.FUN.2026.16,
  author =	{Favreau, Jean-Marie and Gerard, Yan and Lafourcade, Pascal and Robert, L\'{e}o},
  title =	{{Lozenge Tiling by Computing Distances}},
  booktitle =	{13th International Conference on Fun with Algorithms (FUN 2026)},
  pages =	{16:1--16:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-417-8},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{366},
  editor =	{Iacono, John},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2026.16},
  URN =		{urn:nbn:de:0030-drops-257350},
  doi =		{10.4230/LIPIcs.FUN.2026.16},
  annote =	{Keywords: Tiling, Lozenge, Directed Graph, Dicut, Difference Constraints, Bellman-Ford}
}
Document
DOI: 10.4230/LIPIcs.FUN.2026.25
Computational Complexity of Swish Is Solved

Authors: Takashi Horiyama, Takehiro Ito, Jun Kawahara, Shin-ichi Minato, Akira Suzuki, Ryuhei Uehara, and Yutaro Yamaguchi

Published in: LIPIcs, Volume 366, 13th International Conference on Fun with Algorithms (FUN 2026)

Abstract
Swish is a card game in which players are given cards having symbols (hoops and balls), and find a valid superposition of cards, called a "swish." Dailly, Lafourcade, and Marcadet (FUN 2024) studied a generalized version of Swish and showed that the problem is solvable in polynomial time with one symbol per card, while it is NP-complete with three or more symbols per card. In this paper, we resolve the previously open case of two symbols per card, which corresponds to the original game. We show that Swish is NP-complete for this case. Specifically, we prove the NP-hardness when the allowed transformations of cards are restricted to a single (horizontal or vertical) flip or 180-degree rotation, and extend the results to the original setting allowing all three transformations. In contrast, when neither transformation is allowed, we present a polynomial-time algorithm. Combining known and our results, we establish a complete characterization of the computational complexity of Swish with respect to both the number of symbols per card and the allowed transformations.
Cite as

Takashi Horiyama, Takehiro Ito, Jun Kawahara, Shin-ichi Minato, Akira Suzuki, Ryuhei Uehara, and Yutaro Yamaguchi. Computational Complexity of Swish Is Solved. In 13th International Conference on Fun with Algorithms (FUN 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 366, pp. 25:1-25:12, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{horiyama_et_al:LIPIcs.FUN.2026.25,
  author =	{Horiyama, Takashi and Ito, Takehiro and Kawahara, Jun and Minato, Shin-ichi and Suzuki, Akira and Uehara, Ryuhei and Yamaguchi, Yutaro},
  title =	{{Computational Complexity of Swish Is Solved}},
  booktitle =	{13th International Conference on Fun with Algorithms (FUN 2026)},
  pages =	{25:1--25:12},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-417-8},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{366},
  editor =	{Iacono, John},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2026.25},
  URN =		{urn:nbn:de:0030-drops-257448},
  doi =		{10.4230/LIPIcs.FUN.2026.25},
  annote =	{Keywords: Swish, Computational complexity, Matching, Parity-constrained cycles}
}
Document
DOI: 10.4230/LIPIcs.FUN.2026.33
When Locality Implies Globality: Card-Based ZKP Protocol for Shakashaka Puzzle

Authors: Daiki Miyahara, Léo Robert, Pascal Lafourcade, and Shohei Kaneko

Published in: LIPIcs, Volume 366, 13th International Conference on Fun with Algorithms (FUN 2026)

Abstract
Shakashaka is an NP-complete Nikoli puzzle that requires to draw white rectangles by filling a grid with black triangles. Verifying that there are only rectangles drawn in the solution was an open problem for card-based ZKP protocols designers. In this paper, we construct a card-based ZKP protocol to show that a prover can prove to a verifier that he knows a solution of this puzzle without revealing any information. For doing this we prove a local property on all possible 2 × 2 subgrids drawn according to the rules of the game and such configurations are possible valid shapes for rectangles. This local property implies a global property on the shape of the constructed areas. Thanks to this local result for all 2 × 2 subgrids, we are able to establish that the only possible shape in the global grid are rectangles. We also verify other classical rules of Shakashaka.
Cite as

Daiki Miyahara, Léo Robert, Pascal Lafourcade, and Shohei Kaneko. When Locality Implies Globality: Card-Based ZKP Protocol for Shakashaka Puzzle. In 13th International Conference on Fun with Algorithms (FUN 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 366, pp. 33:1-33:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{miyahara_et_al:LIPIcs.FUN.2026.33,
  author =	{Miyahara, Daiki and Robert, L\'{e}o and Lafourcade, Pascal and Kaneko, Shohei},
  title =	{{When Locality Implies Globality: Card-Based ZKP Protocol for Shakashaka Puzzle}},
  booktitle =	{13th International Conference on Fun with Algorithms (FUN 2026)},
  pages =	{33:1--33:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-417-8},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{366},
  editor =	{Iacono, John},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2026.33},
  URN =		{urn:nbn:de:0030-drops-257525},
  doi =		{10.4230/LIPIcs.FUN.2026.33},
  annote =	{Keywords: Card-based cryptography, ShakaShaka, Nikoli, ZKP}
}
Document
DOI: 10.4230/LIPIcs.FUN.2026.34
Playing President with Virtual Players: How to Play Multiple Cards of a Kind

Authors: Daiki Miyahara, Pascal Lafourcade, Takaaki Mizuki, and Kazumasa Shinagawa

Published in: LIPIcs, Volume 366, 13th International Conference on Fun with Algorithms (FUN 2026)

Abstract
President is a popular card game in which players may play one to four cards of the same rank. Since it is less enjoyable with too few human players, to address this, we study the player-simulation problem for President: realizing the moves of a virtual player while keeping its hand hidden. We propose a selection protocol, which selects multiple cards of the same rank uniformly at random from a hidden virtual player’s hand, whose rank exceeds the latest played cards. Our construction reduces the task to secure sorting, so the overall efficiency is dominated by the underlying sorting protocol. To address this bottleneck, we design an efficient sorting protocol, which reduces the number of steps from O(m log m) to O(m), compared to the existing sorting protocols.
Cite as

Daiki Miyahara, Pascal Lafourcade, Takaaki Mizuki, and Kazumasa Shinagawa. Playing President with Virtual Players: How to Play Multiple Cards of a Kind. In 13th International Conference on Fun with Algorithms (FUN 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 366, pp. 34:1-34:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{miyahara_et_al:LIPIcs.FUN.2026.34,
  author =	{Miyahara, Daiki and Lafourcade, Pascal and Mizuki, Takaaki and Shinagawa, Kazumasa},
  title =	{{Playing President with Virtual Players: How to Play Multiple Cards of a Kind}},
  booktitle =	{13th International Conference on Fun with Algorithms (FUN 2026)},
  pages =	{34:1--34:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-417-8},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{366},
  editor =	{Iacono, John},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2026.34},
  URN =		{urn:nbn:de:0030-drops-257535},
  doi =		{10.4230/LIPIcs.FUN.2026.34},
  annote =	{Keywords: Card-Based Cryptography, Player-Simulation Problem, President}
}
Document
DOI: 10.4230/LIPIcs.FUN.2026.35
Card-Based ZKP Protocols for Connectivity-Based Puzzles: Extending to Tree Structures with Application to Nurimeizu

Authors: Daiki Miyahara, Pascal Lafourcade, and Maxime Puys

Published in: LIPIcs, Volume 366, 13th International Conference on Fun with Algorithms (FUN 2026)

Abstract
Card-based zero-knowledge proof (ZKP) protocols allow a prover to convince a verifier that it knows a witness of a given statement, without revealing any information, using a physical deck of playing cards. Previous studies have focused on puzzles with a specific connected component, such as a simple cycle and a polyomino. In this study, we propose a unified approach to handle a family of connected components, including a tree, path, cycle, and polyomino. This approach achieves this verification in O(mn) steps relative to a given grid size m × n. Using this approach, we construct a card-based ZKP protocol for Nurimeizu, where the goal is to find the shortest path on a given grid.
Cite as

Daiki Miyahara, Pascal Lafourcade, and Maxime Puys. Card-Based ZKP Protocols for Connectivity-Based Puzzles: Extending to Tree Structures with Application to Nurimeizu. In 13th International Conference on Fun with Algorithms (FUN 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 366, pp. 35:1-35:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{miyahara_et_al:LIPIcs.FUN.2026.35,
  author =	{Miyahara, Daiki and Lafourcade, Pascal and Puys, Maxime},
  title =	{{Card-Based ZKP Protocols for Connectivity-Based Puzzles: Extending to Tree Structures with Application to Nurimeizu}},
  booktitle =	{13th International Conference on Fun with Algorithms (FUN 2026)},
  pages =	{35:1--35:13},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-417-8},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{366},
  editor =	{Iacono, John},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2026.35},
  URN =		{urn:nbn:de:0030-drops-257547},
  doi =		{10.4230/LIPIcs.FUN.2026.35},
  annote =	{Keywords: Card-based cryptography, Nurimeizu, Nikoli, ZKP}
}
Document
Invited Paper
DOI: 10.4230/OASIcs.RW.2024/2025.6
Explaining Reasoning Results for Description Logic Ontologies (Invited Paper)

Authors: Patrick Koopmann

Published in: OASIcs, Volume 138, Joint Proceedings of the 20th and 21st Reasoning Web Summer Schools (RW 2024 & RW 2025)

Abstract
The Web Ontology Language (OWL), grounded in description logics, enables reasoning systems to infer implicit knowledge in a transparent manner. However, the expressivity of description logics and the complexity of large ontologies often results in reasoning outcomes that are hard to understand without additional tool support. Explanations of these outcomes are essential for users to understand ontology content, communicate its structure and behavior effectively, and debug undesired or missing inferences. This chapter provides an overview of the central explanation techniques that have been developed for explaining reasoning with description logic ontologies. Here, we consider both explanations for positive entailments (explaining why something can be deduced), as well as negative entailments (why something cannot be deduced). More specifically, we discuss justifications, proofs and interpolation as a means to explain positive entailments, and abduction for explaining negative entailments, where we also have a closer look at practical algorithms as well as practical and theoretical challenges.
Cite as

Patrick Koopmann. Explaining Reasoning Results for Description Logic Ontologies (Invited Paper). In Joint Proceedings of the 20th and 21st Reasoning Web Summer Schools (RW 2024 & RW 2025). Open Access Series in Informatics (OASIcs), Volume 138, pp. 6:1-6:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{koopmann:OASIcs.RW.2024/2025.6,
  author =	{Koopmann, Patrick},
  title =	{{Explaining Reasoning Results for Description Logic Ontologies}},
  booktitle =	{Joint Proceedings of the 20th and 21st Reasoning Web Summer Schools (RW 2024 \& RW 2025)},
  pages =	{6:1--6:29},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-405-5},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{138},
  editor =	{Artale, Alessandro and Bienvenu, Meghyn and Garc{\'\i}a, Yazm{\'\i}n Ib\'{a}\~{n}ez and Murlak, Filip},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.RW.2024/2025.6},
  URN =		{urn:nbn:de:0030-drops-250514},
  doi =		{10.4230/OASIcs.RW.2024/2025.6},
  annote =	{Keywords: Explanations, Justifications, Proofs, Craig Interpolation, Contrastive Explanations}
}
Document
DOI: 10.4230/LIPIcs.SAND.2025.10
Fault Detection and Identification by Autonomous Mobile Robots

Authors: Stefano Clemente and Caterina Feletti

Published in: LIPIcs, Volume 330, 4th Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2025)

Abstract
The Look-Compute-Move model (LCM) is adopted to study swarms of mobile robots that have to solve a given problem. Robots are generally assumed to be autonomous, indistinguishable, anonymous, homogeneous and to move on the Euclidean plane. Different LCM sub-models have been theorized to study different settings and their computational power. Notably, the literature has focused on four base models (i.e., OBLOT, FSTA, FCOM, LUMI) that differ in memory and communication capabilities, and in different synchronization modes (e.g., fully synchronous FSYNCH, semi-synchronous SSYNCH). In this paper, we consider fault-prone models where robots can suffer from crash faults: each robot may irremediably stop working after an unpredictable time. We study the general Fault Detection (FD) problem which is solved by a swarm if it correctly detects whether a faulty robot exists in the swarm. The Fault Identification (FI) problem additionally requires identifying which robots are faulty. We consider 12 LCM sub-models (OBLOT, FSTA, FCOM, LUMI, combined with FSYNCH, SSYNCH, and the round-robin RROBIN) and we study the (im)possibility of designing reliable procedures to solve FD or FI. In particular, we propose three distributed algorithms so that a swarm can collectively solve FD under the models LUMI^FSYNCH, FCOM^FSYNCH, and LUMI^RROBIN.
Cite as

Stefano Clemente and Caterina Feletti. Fault Detection and Identification by Autonomous Mobile Robots. In 4th Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 330, pp. 10:1-10:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{clemente_et_al:LIPIcs.SAND.2025.10,
  author =	{Clemente, Stefano and Feletti, Caterina},
  title =	{{Fault Detection and Identification by Autonomous Mobile Robots}},
  booktitle =	{4th Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2025)},
  pages =	{10:1--10:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-368-3},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{330},
  editor =	{Meeks, Kitty and Scheideler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SAND.2025.10},
  URN =		{urn:nbn:de:0030-drops-230639},
  doi =		{10.4230/LIPIcs.SAND.2025.10},
  annote =	{Keywords: Autonomous mobile robots, Faulty robots, Look-Compute-Move, Fault detection, Fault identification, Round-robin}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2024.12
Crash-Tolerant Perpetual Exploration with Myopic Luminous Robots on Rings

Authors: Fukuhito Ooshita, Naoki Kitamura, Ryota Eguchi, Michiko Inoue, Hirotsugu Kakugawa, Sayaka Kamei, Masahiro Shibata, and Yuichi Sudo

Published in: LIPIcs, Volume 324, 28th International Conference on Principles of Distributed Systems (OPODIS 2024)

Abstract
We investigate crash-tolerant perpetual exploration algorithms by myopic luminous robots on ring networks. Myopic robots mean that they can observe nodes only within a certain fixed distance ϕ, and luminous robots mean that they have light devices that can emit a color from a set of colors. The goal of perpetual exploration is to ensure that robots, starting from specific initial positions and colors, move in such a way that every node is visited by at least one robot infinitely often. As a main contribution, we clarify the tight necessary and sufficient number of robots to realize perpetual exploration when at most f robots crash. In the fully synchronous model, we prove that f+2 robots are necessary and sufficient for any ϕ ≥ 1. In the semi-synchronous and asynchronous models, we prove that 3f+3 (resp., 2f+2) robots are necessary and sufficient if ϕ = 1 (resp., ϕ ≥ 2).
Cite as

Fukuhito Ooshita, Naoki Kitamura, Ryota Eguchi, Michiko Inoue, Hirotsugu Kakugawa, Sayaka Kamei, Masahiro Shibata, and Yuichi Sudo. Crash-Tolerant Perpetual Exploration with Myopic Luminous Robots on Rings. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 12:1-12:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{ooshita_et_al:LIPIcs.OPODIS.2024.12,
  author =	{Ooshita, Fukuhito and Kitamura, Naoki and Eguchi, Ryota and Inoue, Michiko and Kakugawa, Hirotsugu and Kamei, Sayaka and Shibata, Masahiro and Sudo, Yuichi},
  title =	{{Crash-Tolerant Perpetual Exploration with Myopic Luminous Robots on Rings}},
  booktitle =	{28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
  pages =	{12:1--12:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-360-7},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{324},
  editor =	{Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.12},
  URN =		{urn:nbn:de:0030-drops-225486},
  doi =		{10.4230/LIPIcs.OPODIS.2024.12},
  annote =	{Keywords: mobile robots, crash faults, LCM model, exploration}
}
Document
DOI: 10.4230/LIPIcs.FUN.2024.10
How Did They Design This Game? Swish: Complexity and Unplayable Positions

Authors: Antoine Dailly, Pascal Lafourcade, and Gaël Marcadet

Published in: LIPIcs, Volume 291, 12th International Conference on Fun with Algorithms (FUN 2024)

Abstract
Swish is a competitive pattern recognition card-based game, in which players are trying to find a valid cards superposition from a set of cards, called a "swish". By the nature of the game, one may expect to easily recover the logic of the Swish’s designers. However, no justification appears to explain the number of cards, of duplicates, but also under which circumstances no player can find a swish. In this work, we formally investigate Swish. In the commercial version of the game, we observe that there exist large sets of cards with no swish, and find a construction to generate large sets of cards without swish. More importantly, in the general case with larger cards, we prove that Swish is NP-complete.
Cite as

Antoine Dailly, Pascal Lafourcade, and Gaël Marcadet. How Did They Design This Game? Swish: Complexity and Unplayable Positions. In 12th International Conference on Fun with Algorithms (FUN 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 291, pp. 10:1-10:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{dailly_et_al:LIPIcs.FUN.2024.10,
  author =	{Dailly, Antoine and Lafourcade, Pascal and Marcadet, Ga\"{e}l},
  title =	{{How Did They Design This Game? Swish: Complexity and Unplayable Positions}},
  booktitle =	{12th International Conference on Fun with Algorithms (FUN 2024)},
  pages =	{10:1--10:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-314-0},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{291},
  editor =	{Broder, Andrei Z. and Tamir, Tami},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2024.10},
  URN =		{urn:nbn:de:0030-drops-199185},
  doi =		{10.4230/LIPIcs.FUN.2024.10},
  annote =	{Keywords: Game, Complexity, Algorithms}
}
Document
DOI: 10.4230/LITES.8.2.2
Swarms of Mobile Robots: Towards Versatility with Safety

Authors: Pierre Courtieu, Lionel Rieg, Sébastien Tixeuil, and Xavier Urbain

Published in: LITES, Volume 8, Issue 2 (2022): Special Issue on Distributed Hybrid Systems. Leibniz Transactions on Embedded Systems, Volume 8, Issue 2

Abstract
We present Pactole, a formal framework to design and prove the correctness of protocols (or the impossibility of their existence) that target mobile robotic swarms. Unlike previous approaches, our methodology unifies in a single formalism the execution model, the problem specification, the protocol, and its proof of correctness. The Pactole framework makes use of the Coq proof assistant, and is specially targeted at protocol designers and problem specifiers, so that a common unambiguous language is used from the very early stages of protocol development. We stress the underlying framework design principles to enable high expressivity and modularity, and provide concrete examples about how the Pactole framework can be used to tackle actual problems, some previously addressed by the Distributed Computing community, but also new problems, while being certified correct.
Cite as

Pierre Courtieu, Lionel Rieg, Sébastien Tixeuil, and Xavier Urbain. Swarms of Mobile Robots: Towards Versatility with Safety. In LITES, Volume 8, Issue 2 (2022): Special Issue on Distributed Hybrid Systems. Leibniz Transactions on Embedded Systems, Volume 8, Issue 2, pp. 02:1-02:36, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@Article{courtieu_et_al:LITES.8.2.2,
  author =	{Courtieu, Pierre and Rieg, Lionel and Tixeuil, S\'{e}bastien and Urbain, Xavier},
  title =	{{Swarms of Mobile Robots: Towards Versatility with Safety}},
  journal =	{Leibniz Transactions on Embedded Systems},
  pages =	{02:1--02:36},
  ISSN =	{2199-2002},
  year =	{2022},
  volume =	{8},
  number =	{2},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LITES.8.2.2},
  URN =		{urn:nbn:de:0030-drops-192942},
  doi =		{10.4230/LITES.8.2.2},
  annote =	{Keywords: distributed algorithm, mobile autonomous robots, formal proof}
}
Document
CG Challenge
DOI: 10.4230/LIPIcs.SoCG.2022.73
Local Search with Weighting Schemes for the CG:SHOP 2022 Competition (CG Challenge)

Authors: Florian Fontan, Pascal Lafourcade, Luc Libralesso, and Benjamin Momège

Published in: LIPIcs, Volume 224, 38th International Symposium on Computational Geometry (SoCG 2022)

Abstract
This paper describes the heuristics used by the LASAOFOOFUBESTINNRRALLDECA team for the CG:SHOP 2022 challenge. We introduce a new greedy algorithm that exploits information about the challenge instances, and hybridize two classical local-search schemes with weighting schemes. We found 211/225 best-known solutions. Hence, with the algorithms presented in this article, our team was able to reach the 3rd place of the challenge, among 40 participating teams.
Cite as

Florian Fontan, Pascal Lafourcade, Luc Libralesso, and Benjamin Momège. Local Search with Weighting Schemes for the CG:SHOP 2022 Competition (CG Challenge). In 38th International Symposium on Computational Geometry (SoCG 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 224, pp. 73:1-73:6, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{fontan_et_al:LIPIcs.SoCG.2022.73,
  author =	{Fontan, Florian and Lafourcade, Pascal and Libralesso, Luc and Mom\`{e}ge, Benjamin},
  title =	{{Local Search with Weighting Schemes for the CG:SHOP 2022 Competition}},
  booktitle =	{38th International Symposium on Computational Geometry (SoCG 2022)},
  pages =	{73:1--73:6},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-227-3},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{224},
  editor =	{Goaoc, Xavier and Kerber, Michael},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2022.73},
  URN =		{urn:nbn:de:0030-drops-160811},
  doi =		{10.4230/LIPIcs.SoCG.2022.73},
  annote =	{Keywords: heuristics, vertex coloring, digital geometry}
}
Document
DOI: 10.4230/LIPIcs.FUN.2022.7
Beedroids: How Luminous Autonomous Swarms of UAVs Can Save the World?

Authors: Quentin Bramas, Stéphane Devismes, Anaïs Durand, Pascal Lafourcade, and Anissa Lamani

Published in: LIPIcs, Volume 226, 11th International Conference on Fun with Algorithms (FUN 2022)

Abstract
Bee extinction is a great risk for humanity. To circumvent this ineluctable disaster, we propose to develop beedroids, i.e., small UAVs mimicking the behaviors of real bees. Those beedroids are endowed with very weak capabilities (short-range visibility sensors, no GPS, light with a few colors, ...). Like real bees, they have to self-organize together into swarms. Beedroid swarms will be deployed in cuboid-shaped greenhouse. Each beedroid swarm will have to indefinitely search for flowers to pollinate in its greenhouse. We model this problem as a perpetual exploration of a 3D grid by a swarm of beedroids. In this paper, we propose two optimal solutions to solve this problem and so to save humanity.
Cite as

Quentin Bramas, Stéphane Devismes, Anaïs Durand, Pascal Lafourcade, and Anissa Lamani. Beedroids: How Luminous Autonomous Swarms of UAVs Can Save the World?. In 11th International Conference on Fun with Algorithms (FUN 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 226, pp. 7:1-7:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bramas_et_al:LIPIcs.FUN.2022.7,
  author =	{Bramas, Quentin and Devismes, St\'{e}phane and Durand, Ana\"{i}s and Lafourcade, Pascal and Lamani, Anissa},
  title =	{{Beedroids: How Luminous Autonomous Swarms of UAVs Can Save the World?}},
  booktitle =	{11th International Conference on Fun with Algorithms (FUN 2022)},
  pages =	{7:1--7:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-232-7},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{226},
  editor =	{Fraigniaud, Pierre and Uno, Yushi},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2022.7},
  URN =		{urn:nbn:de:0030-drops-159771},
  doi =		{10.4230/LIPIcs.FUN.2022.7},
  annote =	{Keywords: Bee extinction, luminous swarms of beedroids, perpetual flower pollination problem, greenhouse}
}
Document
DOI: 10.4230/LIPIcs.CP.2021.40
Automatic Generation of Declarative Models For Differential Cryptanalysis

Authors: Luc Libralesso, François Delobel, Pascal Lafourcade, and Christine Solnon

Published in: LIPIcs, Volume 210, 27th International Conference on Principles and Practice of Constraint Programming (CP 2021)

Abstract
When designing a new symmetric block cipher, it is necessary to evaluate its robustness against differential attacks. This is done by computing Truncated Differential Characteristics (TDCs) that provide bounds on the complexity of these attacks. TDCs are often computed by using declarative approaches such as CP (Constraint Programming), SAT, or ILP (Integer Linear Programming). However, designing accurate and efficient models for these solvers is a difficult, error-prone and time-consuming task, and it requires advanced skills on both symmetric cryptography and solvers. In this paper, we describe a tool for automatically generating these models, called Tagada (Tool for Automatic Generation of Abstraction-based Differential Attacks). The input of Tagada is an operational description of the cipher by means of black-box operators and bipartite Directed Acyclic Graphs (DAGs). Given this description, we show how to automatically generate constraints that model operator semantics, and how to generate MiniZinc models. We experimentally evaluate our approach on two different kinds of differential attacks (e.g., single-key and related-key) and four different symmetric block ciphers (e.g., the AES (Advanced Encryption Standard), Craft, Midori, and Skinny). We show that our automatically generated models are competitive with state-of-the-art approaches. These automatically generated models constitute a new benchmark composed of eight optimization problems and eight enumeration problems, with instances of increasing size in each problem. We experimentally compare CP, SAT, and ILP solvers on this new benchmark.
Cite as

Luc Libralesso, François Delobel, Pascal Lafourcade, and Christine Solnon. Automatic Generation of Declarative Models For Differential Cryptanalysis. In 27th International Conference on Principles and Practice of Constraint Programming (CP 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 210, pp. 40:1-40:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{libralesso_et_al:LIPIcs.CP.2021.40,
  author =	{Libralesso, Luc and Delobel, Fran\c{c}ois and Lafourcade, Pascal and Solnon, Christine},
  title =	{{Automatic Generation of Declarative Models For Differential Cryptanalysis}},
  booktitle =	{27th International Conference on Principles and Practice of Constraint Programming (CP 2021)},
  pages =	{40:1--40:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-211-2},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{210},
  editor =	{Michel, Laurent D.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CP.2021.40},
  URN =		{urn:nbn:de:0030-drops-153314},
  doi =		{10.4230/LIPIcs.CP.2021.40},
  annote =	{Keywords: Constraint Programming, SAT, ILP, Differential Cryptanalysis}
}
Document
CG Challenge
DOI: 10.4230/LIPIcs.SoCG.2021.63
Shadoks Approach to Low-Makespan Coordinated Motion Planning (CG Challenge)

Authors: Loïc Crombez, Guilherme D. da Fonseca, Yan Gerard, Aldo Gonzalez-Lorenzo, Pascal Lafourcade, and Luc Libralesso

Published in: LIPIcs, Volume 189, 37th International Symposium on Computational Geometry (SoCG 2021)

Abstract
This paper describes the heuristics used by the Shadoks team for the CG:SHOP 2021 challenge on motion planning. Using the heuristics outlined in this paper, our team won first place with the best solution to 202 out of 203 instances and optimal solutions to at least 105 of them.
Cite as

Loïc Crombez, Guilherme D. da Fonseca, Yan Gerard, Aldo Gonzalez-Lorenzo, Pascal Lafourcade, and Luc Libralesso. Shadoks Approach to Low-Makespan Coordinated Motion Planning (CG Challenge). In 37th International Symposium on Computational Geometry (SoCG 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 189, pp. 63:1-63:9, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{crombez_et_al:LIPIcs.SoCG.2021.63,
  author =	{Crombez, Lo\"{i}c and da Fonseca, Guilherme D. and Gerard, Yan and Gonzalez-Lorenzo, Aldo and Lafourcade, Pascal and Libralesso, Luc},
  title =	{{Shadoks Approach to Low-Makespan Coordinated Motion Planning}},
  booktitle =	{37th International Symposium on Computational Geometry (SoCG 2021)},
  pages =	{63:1--63:9},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-184-9},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{189},
  editor =	{Buchin, Kevin and Colin de Verdi\`{e}re, \'{E}ric},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2021.63},
  URN =		{urn:nbn:de:0030-drops-138622},
  doi =		{10.4230/LIPIcs.SoCG.2021.63},
  annote =	{Keywords: heuristics, motion planning, digital geometry, shortest path}
}
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