Parameterized Verification of Algorithms for Oblivious Robots on a Ring

We study verification problems for autonomous swarms of mobile robots that self-organize and cooperate to solve global objectives. In particular, we focus in this paper on the model proposed by Suzuki and Yamashita of anonymous robots evolving in a discrete space with a finite number of locations (here, a ring). A large number of algorithms have been proposed working for rings whose size is not a priori fixed and can be hence considered as a parameter. Handmade correctness proofs of these algorithms have been shown to be error-prone, and recent attention had been given to the application of formal methods to automatically prove those. Our work is the first to study the verification problem of such algorithms in the parameter-ized case. We show that safety and reachability problems are undecidable for robots evolving asynchronously. On the positive side, we show that safety properties are decidable in the synchronous case, as well as in the asynchronous case for a particular class of algorithms. Several properties on the protocol can be decided as well. Decision procedures rely on an encoding in Presburger arithmetics formulae that can be verified by an SMT-solver. Feasibility of our approach is demonstrated by the encoding of several case studies

A Certified Universal Gathering Algorithm for Oblivious Mobile Robots

We present a new algorithm for the problem of universal gathering mobile oblivious robots (that is, starting from any initial configuration that is not bivalent, using any number of robots, the robots reach in a finite number of steps the same position, not known beforehand) without relying on a common chirality. We give very strong guaranties on the correctness of our algorithm by proving formally that it is correct, using the COQ proof assistant. To our knowledge, this is the first certified positive (and constructive) result in the context of oblivious mobile robots. It demonstrates both the effectiveness of the approach to obtain new algorithms that are truly generic, and its managability since the amount of developped code remains human readable

Certified Universal Gathering in R2R^2 for Oblivious Mobile Robots

We present a unified formal framework for expressing mobile robots models, protocols, and proofs, and devise a protocol design/proof methodology dedicated to mobile robots that takes advantage of this formal framework. As a case study, we present the first formally certified protocol for oblivious mobile robots evolving in a two-dimensional Euclidean space. In more details, we provide a new algorithm for the problem of universal gathering mobile oblivious robots (that is, starting from any initial configuration that is not bivalent, using any number of robots, the robots reach in a finite number of steps the same position, not known beforehand) without relying on a common orientation nor chirality. We give very strong guaranties on the correctness of our algorithm by proving formally that it is correct, using the COQ proof assistant. This result demonstrates both the effectiveness of the approach to obtain new algorithms that use as few assumptions as necessary, and its manageability since the amount of developed code remains human readable.Comment: arXiv admin note: substantial text overlap with arXiv:1506.0160

Certified Impossibility Results for Byzantine-Tolerant Mobile Robots

We propose a framework to build formal developments for robot networks using the COQ proof assistant, to state and to prove formally various properties. We focus in this paper on impossibility proofs, as it is natural to take advantage of the COQ higher order calculus to reason about algorithms as abstract objects. We present in particular formal proofs of two impossibility results forconvergence of oblivious mobile robots if respectively more than one half and more than one third of the robots exhibit Byzantine failures, starting from the original theorems by Bouzid et al.. Thanks to our formalization, the corresponding COQ developments are quite compact. To our knowledge, these are the first certified (in the sense of formally proved) impossibility results for robot networks

Impossibility of Gathering, a Certification

Recent advances in Distributed Computing highlight models and algorithms for autonomous swarms of mobile robots that self-organise and cooperate to solve global objectives. The overwhelming majority of works so far considers handmade algorithms and proofs of correctness. This paper builds upon a previously proposed formal framework to certify the correctness of impossibility results regarding distributed algorithms that are dedicated to autonomous mobile robots evolving in a continuous space. As a case study, we consider the problem of gathering all robots at a particular location, not known beforehand. A fundamental (but not yet formally certified) result, due to Suzuki and Yamashita, states that this simple task is impossible for two robots executing deterministic code and initially located at distinct positions. Not only do we obtain a certified proof of the original impossibility result, we also get the more general impossibility of gathering with an even number of robots, when any two robots are possibly initially at the same exact location.Comment: 10

Company-Coq: Taking Proof General one step closer to a real IDE

Company-Coq is a new Emacs package that extends Proof General with a contextual auto-completion engine for Coq proofs and many additional facilities to make writing proofs easier and more efficient. Beyond fuzzy auto-completion of tactics, options, module names, and local definitions, company-coq offers offline in-editor documentation, convenient snippets, and multiple other Coq-specific IDE features. The system will be presented at CoqPL 2016, focusing on a live demo with an emphasis on writing proofs in Emacs more efficiently, and a discussion of desirable features of proof-oriented development environments. https://github.com/cpitclaudel/company-co

Roman d’aventure et événement. Pour une littérature (vraiment) populaire

Questioning the place of the event in the fiction narrative through naturalism in turn led some writers – such as Stevenson, London, Conrad – to set it at the core of the plot itself. This pre-eminence might then well be used as a standard for a literature known as « popular ». Those writers – whose lineage is huge in comics, crime fiction and cinema – have the « hero » become the one to be faced with the very events he or she causes to happen, and which henceforth makes up the core of any narrative. The latest avatar of those seesaw movements can be found in the modern generalization of « storytelling », a trend which responds to the New French Fiction, for example. Couldn't this contemporary obsession for 'storytelling' then be the sign of what purports to be a reenchantment of the world, as if it was not possible to contemplate the world in any other way than rife with events through which alone it can make sense

Passerelles. Dialogues d’écrivains autour du silence

The article deals with the question of the relationship between silence and language among writers. It centers around two themes: first, the place of silence in human relations; second, the silence of the world, or, on the contrary, the voices that spring up from it. This article has a lot of writers debate upon these themes, some being rather perceptive to the positive qualities of the silence of the world and/or of their fellow men, others rather gloomy when seeing theim possibility of hearing the world, or of having more genuine relations with others

Analyse ponctuelle des inclusions fluides dans les minéraux par ablation laser femtoseconde ICP-MS : développements et validation

Le but de cette thèse est de valider l'utilisation d'un laser femtoseconde à lumière infrarouge comme alternative efficace pour l'ablation contrôlée et reproductible d'inclusions fluides naturelles ou synthétiques. Nous avons étudié le comportement du quartz à l'ablation femtoseconde infrarouge, et nous avons pu mesurer des seuils d'ablation de 0,06 à 2,9 J.cm-2 en fonction de l'état de surface de l'échantillon. Des taux d'ablation ont été calculés sur les 1000 premiers tirs d'ablation : 0,58 µm/tir constant pour une lentille longue focale, de 0,42 à 0,02 µm/tir pour un objectif à focale courte. Nous nous sommes intéressés en premier lieu aux effets de matrices lors de l'ablation femtoseconde de trois échantillons de matrices différentes, utilisés comme standards externes pour l'analyse LA-ICP-MS des inclusions fluides : des inclusions synthétiques, des capillaires et des verres synthétiques NIST. Aucun effet de matrice n'a été constaté, et le couplage capillaires - verres NIST donne les meilleurs résultats de calibrage des inclusions fluides sur un grand nombre d'éléments, notamment le chlorure. Nous avons ensuite mesuré des concentrations d'éléments dans des inclusions fluides naturelles. Les concentrations s'étalent sur 6 ordres de grandeurs, avec des limites de détection en accord avec la littérature. Ces résultats ont été comparés à des méthodes destructives validées pour l'étude des inclusions fluides, le LIBS et l'ablation laser ICP-MS nanoseconde. La comparaison des trois méthodes a permis de mettre en évidence la faisabilité du laser femtoseconde comme système d'ablation pour l'étude des inclusions fluides.This thesis aims to validate the use of an infrared femtosecond laser as a valid alternative for controlled and reproducible LA-ICP-MS studies of natural or synthetic fluid inclusions. The ablation behaviour of quartz using the infrared femtosecond laser has been studied, and ablation thresholds were calculated from 0.06 to 2.9 J.cm-2 depending on the sample surface condition. Ablation rates were also studied in the first 1000 laser shots. They are strongly related to the ablation optic (and thus the focal length of the optical setup). Using a long-focal lens, ablation rate was constant and equal to 0.57µm/shot, whereas using a short-focal objective, rates starts at 0.42 and diminishes to 0.02 µm/shot. Matrix effects during ablation were studied using three common external standards for LA-ICP-MS studies of fluid inclusions: synthetic fluid inclusion, glass microcapillaries and NIST standard glasses. No matrix effect was observed, and using both microcapillaries and NIST standard glasses as external standard for LA-ICP-MS studies of fluid inclusions gives the most reproducible results for a large number of chemical elements, even for chlorine. Femtosecond LA-ICP-MS studies were finally carried out on natural, highly saline fluid inclusions. Concentrations were measured on six orders of magnitude, and limits of detection were comparable to literature. These concentrations were then compared to other destructive method: LIBS and nanosecond ultraviolet LA-ICP-MS of fluid inclusions. Comparison between the three methods proved that femtosecond infrared lasers are a viable option for LA-ICP-MS studies of fluid inclusions

Une preuve est une histoire

International audienceLa narration computationnelle est un sous-domaine de l'Intelligence Artificielle, lié notamment aux problèmes de représentation des connaissances et en particulier à la représentation des actions et du changement. On s'y intéresse aux objets narratifs (littéraires, interactifs, cinématographiques) pour les comprendre, les analyser, ou les construire, en proposant des techniques qui peuvent être mises en oeuvre par des programmes et systèmes informatiques. C'est un domaine qui a des applications dans le domaine des jeux vidéos ou jeux utiles par exemple. Nous proposons de revenir dans cet exposé sur la motivation et les fondements d'un travail en cours, qui repose sur une connivence entre la structure des preuves en logique linéaire et la structure d'histoires interactives. Bien qu'ayant déjà donné lieu à une interprétation opérationnelle, cette approche a laissé des pistes inexplorées, surtout en ce qui concerne une normalisation et modularité de preuves/histoires dans un sous-ensemble ad hoc de la logique linéaire. Certaines idées ont été explorées en 2011 à l'aide de Coq et nous aimerions partager et échanger au sujet de nos projets actuels pour approfondir ce travail