JournalslemVol. 63, No. 1/2pp. 1–18Bulletin bibliographiqueDownload PDFA subscription is required to access this article.Cite this articleBulletin bibliographique. Enseign. Math. 63 (2017), no. 1/2, pp. 1–18DOI 10.4171/LEM/63-1/2-10
