[Alta-Logic] Peripatetic Seminar tomorrow: Stacks with Masoud

[Robin Cockett]

Speaker: Masoud Kamgar

Time: 11:00am Wed 17 Nov.

Place: ICT 616

Title: What is a stack? 

Abstract: Stacks were invented by Grothendieck in the sixties as a part 
of his program which revolutionized our understanding of spaces. 
As a first step, one interprets a space X as a sheaf. A sheaf F is a map 
which attaches to every open subspace U->X a set F(U). Grothendieck had 
two main insights about the previous sentence: 

i. One can replace open sets by other objects related to X (for 
instance, covers of X). This gave rise to topos theory (which is also 
relevant in logic, see 
http://en.wikipedia.org/wiki/Background_and_genesis_of_topos_theory).
ii. One can replace the set F(U) by an n-groupoid where n is a positive 
integer or infinity. 

Both i and ii are relevant to the story of stacks. In this talk, we 
focus on the second insight of Grothendieck and take n=1. 

Familiarity with categories and functors are essential. If necessary, I 
can recall the relevant notions.