Groupoids and Noncommutative Geometry Seminar 

22/02/2007, 11:00 — 12:00 — Room P4.35, Mathematics Building
Olivier Brahic, CAMGSD

The restriction functor as a principal bundle

I will explain how bitorsors can act on extensions. This enables us, using categorical language, to see the restriction functor introduced in the previous talk as an almost principal bundle. Besides, we will see that its lack of surjectivity can be measured by a 2-cohomology class.