Etale cohomology reading seminar

Ô la nostalgie à retrouver de vieilles cartes postales. Où le ciel est toujours bleu l'arbre toujours vert la mer étale...

Jmer étale aux Brochet, Artiste : kerzanet jacques

Welcome to our reading seminar in étale cohomology!

We will be mostly following the text "Introduction to Étale Cohomology" by Günter Tamme, although other sources will likely be used as well.

Communication outside of our scheduled meetings will take place on the "Torsor Lounge" discord server. If you would like to join our activities, and have not yet received an invite, please send me an email at:


Each meeting, we'll have a volunteer or combination of volunteers go over specific pieces of material. Between the meetings, I'll suggest some examples, problems or additional sub-topics to work on/discuss.

You can use the discord server as well as the Zoom meeting (which will be left continually open) to discuss material between meetings.

Outline of topics

  • Grothendieck topologies
  • Presheaves and sheaves, cohomology
  • Spectral sequence review
  • Cech cohomology spectral sequence
  • Leray spectral sequence
  • Etale morphisms and the étale topology
  • The étale site over the spectrum of a field
  • Stalks, henselian and strictly henselian rings
  • The Artin-Leray spectral sequence
  • Constructible sheaves
  • Comparison with Betti cohomology
  • Proper base change and applications