Explained role that Azumaya algebras play in the Picard 3-group.

]]>Added some equivalent and more conceptual definitions of “Azumaya algebra”.

]]>earlier today I had added at *Azumaya algebra* a new section *In terms of (derived) étale cohomology* with some notes that I took during a talk by David Gepner. He has a quite beautiful picture. Maybe I find the time to expand a bit on this entry and related entries.