A Challenge Set Approach to Evaluating Machine Translation

Neural machine translation represents an exciting leap forward in translation quality. But what longstanding weaknesses does it resolve, and which remain? We address these questions with a challenge set approach to translation evaluation and error analysis. A challenge set consists of a small set of sentences, each hand-designed to probe a system's capacity to bridge a particular structural divergence between languages. To exemplify this approach, we present an English-French challenge set, and use it to analyze phrase-based and neural systems. The resulting analysis provides not only a more fine-grained picture of the strengths of neural systems, but also insight into which linguistic phenomena remain out of reach.Comment: EMNLP 2017. 28 pages, including appendix. Machine readable data included in a separate file. This version corrects typos in the challenge se

Limits of contraction groups and the Tits core

The Tits core G^+ of a totally disconnected locally compact group G is defined as the abstract subgroup generated by the closures of the contraction groups of all its elements. We show that a dense subgroup is normalised by the Tits core if and only if it contains it. It follows that every dense subnormal subgroup contains the Tits core. In particular, if G is topologically simple, then the Tits core is abstractly simple, and if G^+ is non-trivial then it is the unique minimal dense normal subgroup. The proofs are based on the fact, of independent interest, that the map which associates to an element the closure of its contraction group is continuous.Comment: 11 page

Convergence of a Finite Volume Scheme for a Corrosion Model

In this paper, we study the numerical approximation of a system of partial dif-ferential equations describing the corrosion of an iron based alloy in a nuclear waste repository. In particular, we are interested in the convergence of a numerical scheme consisting in an implicit Euler scheme in time and a Scharfetter-Gummel finite volume scheme in space

D’une langue à l’universel : La France et la francophonie

Si la francophonie n’a pas été une idée française, elle est devenue l’horizon d’un pays qui ne contribuera à la construction d’une Europe démocratique qu’en défendant son identité. Cette dernière n’a de sens que dans la perspective d’un dialogue où la diversité linguistique continuera d’être cultivée à travers le monde. De par l’histoire et la géographie, la langue française a pourtant un destin où s’inscrivent aujourd’hui des enjeux de civilisation à l’échelle universelle.While the Francophonie was not a French idea, it became the horizon of a country that contributed to the construction of a democratie Europe only by defending its identity. The latter makes sense only in a dialogue that embraces and cultivates linguistic diversity. Thanks to history and geography, the destiny of the French language can be found today among the great issues and debates of civilisation

On the residual and profinite closures of commensurated subgroups

The residual closure of a subgroup $H$ of a group $G$ is the intersection of all virtually normal subgroups of $G$ containing $H$. We show that if $G$ is generated by finitely many cosets of $H$ and if $H$ is commensurated, then the residual closure of $H$ in $G$ is virtually normal. This implies that separable commensurated subgroups of finitely generated groups are virtually normal. A stream of applications to separable subgroups, polycyclic groups, residually finite groups, groups acting on trees, lattices in products of trees and just-infinite groups then flows from this main result.Comment: 22 page