A Bi-Directional Refinement Algorithm for the Calculus of (Co)Inductive Constructions

The paper describes the refinement algorithm for the Calculus of (Co)Inductive Constructions (CIC) implemented in the interactive theorem prover Matita. The refinement algorithm is in charge of giving a meaning to the terms, types and proof terms directly written by the user or generated by using tactics, decision procedures or general automation. The terms are written in an "external syntax" meant to be user friendly that allows omission of information, untyped binders and a certain liberal use of user defined sub-typing. The refiner modifies the terms to obtain related well typed terms in the internal syntax understood by the kernel of the ITP. In particular, it acts as a type inference algorithm when all the binders are untyped. The proposed algorithm is bi-directional: given a term in external syntax and a type expected for the term, it propagates as much typing information as possible towards the leaves of the term. Traditional mono-directional algorithms, instead, proceed in a bottom-up way by inferring the type of a sub-term and comparing (unifying) it with the type expected by its context only at the end. We propose some novel bi-directional rules for CIC that are particularly effective. Among the benefits of bi-directionality we have better error message reporting and better inference of dependent types. Moreover, thanks to bi-directionality, the coercion system for sub-typing is more effective and type inference generates simpler unification problems that are more likely to be solved by the inherently incomplete higher order unification algorithms implemented. Finally we introduce in the external syntax the notion of vector of placeholders that enables to omit at once an arbitrary number of arguments. Vectors of placeholders allow a trivial implementation of implicit arguments and greatly simplify the implementation of primitive and simple tactics

Structural Insights into Viral Determinants of Nematode Mediated Grapevine fanleaf virus Transmission

Many animal and plant viruses rely on vectors for their transmission from host to host. Grapevine fanleaf virus (GFLV), a picorna-like virus from plants, is transmitted specifically by the ectoparasitic nematode Xiphinema index. The icosahedral capsid of GFLV, which consists of 60 identical coat protein subunits (CP), carries the determinants of this specificity. Here, we provide novel insight into GFLV transmission by nematodes through a comparative structural and functional analysis of two GFLV variants. We isolated a mutant GFLV strain (GFLV-TD) poorly transmissible by nematodes, and showed that the transmission defect is due to a glycine to aspartate mutation at position 297 (Gly297Asp) in the CP. We next determined the crystal structures of the wild-type GFLV strain F13 at 3.0 Å and of GFLV-TD at 2.7 Å resolution. The Gly297Asp mutation mapped to an exposed loop at the outer surface of the capsid and did not affect the conformation of the assembled capsid, nor of individual CP molecules. The loop is part of a positively charged pocket that includes a previously identified determinant of transmission. We propose that this pocket is a ligand-binding site with essential function in GFLV transmission by X. index. Our data suggest that perturbation of the electrostatic landscape of this pocket affects the interaction of the virion with specific receptors of the nematode's feeding apparatus, and thereby severely diminishes its transmission efficiency. These data provide a first structural insight into the interactions between a plant virus and a nematode vector

Basic completion strategies as another application of the Maude strategy language

The two levels of data and actions on those data provided by the separation between equations and rules in rewriting logic are completed by a third level of strategies to control the application of those actions. This level is implemented on top of Maude as a strategy language, which has been successfully used in a wide range of applications. First we summarize the Maude strategy language design and review some of its applications; then, we describe a new case study, namely the description of completion procedures as transition rules + control, as proposed by Lescanne.Comment: In Proceedings WRS 2011, arXiv:1204.531

Tiré à Part MATISSE: Advanced Earth Modeling for Imaging and Scene Simulation MATISSE: Advanced Earth Modeling for Imaging and Scene Simulation MATISSE : Modélisation Avancée de la Terre pour l'Imagerie et la Simulation des Scènes et de leur Environnement

Résumé Résumé : Le but de MATISSE1.1 est le calcul d'images en luminance spectrale ou intégrée de fonds naturels, ainsi que la transmission d'une signature de gaz chaud. La bande spectrale pour cette version s'étend de 750 à 3300 cm . L'absorption gazeuze est calculée avec un modèle en K corrélé (CK). La variabilité spatiale des grandeurs atmosphériques (température, rapports de mélange, ...) est prise en compte par l'utilisation de profils atmosphériques évoluant le long de la ligne de visée. Les fonds naturels sont constitués du fond atmosphérique, des nuages basse altitude et du fond de sol. Les modèles de rayonnement utilisés sont adaptés à la basse résolution spatiale, ce qui a motivé l'insertion d'un modèle de texture en luminance afin d'accroître la résolution spatiale au domaine décamétrique. Des sorties intermédiaires du programme permettent d'obtenir la luminance et la transmission le long d'une seule ligne de visée, auquel cas les effets de réfraction sont pris en compte. Le long de cette ligne de visée la transmission peut être calculée en utilisant un modèle raie par raie, afin de pouvoir propager le rayonnement issu d'une signature de gaz chaud (feux, jet d'avion ou de missile). ABSTRACT The purpose of MATISSE 1.1 is to compute spectral or integrated radiance images of natural background, as well as the transmission of a hot gas signature. The spectral bandwith for this version of the code is from 750 to 3300 cm -1 (3 to 13 µm) with a 5 cm -1 resolution. Gaseous absorption is computed by a Correlated K (CK) model. The spatial variability of atmospheric quantities (temperatures and mixing ratios, among others) is taken into account by using variable profiles along the line of sight. Natural backgrounds include the atmospheric background, low altitude clouds and the Earth ground. The radiation models used are designed for observation at low spatial resolution of clouds and soils, so a texture model was developed to increase the high spatial resolution rendering in the decametric range. Intermediate outputs of the code deliver radiance and transmission restricted to a single line of sight, in which case atmospheric refraction effects are taken into account. Along this line of sight the transmission can also be computed using a line-byline model, which is usefull to propagate the radiation emitted by a hot gas signature (fires, aircraft or missile plume)

Tests of open-loop LGS tomography with CANARY

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CANARY Phase B: the LGS upgrade to the CANARY tomographic MOAO pathfinder

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CANARY Phase B: the LGS upgrade to the CANARY tomographic MOAO pathfinder

International audienc