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A topos is a category that behaves very much like the category of sets and possesses a good notion of localization. Related to topos are: sheaves, presheaves, descent, stacks, localization,...

14 votes
2 answers
681 views

Who introduced the notion of 2-categories?

Wikipedia seems to have an answer "The concept of 2-category was first introduced by Charles Ehresmann in his work on enriched categories in 1965. The more general concept of bicategory (or weak 2-cat …
user234212323's user avatar
11 votes
1 answer
678 views

A non-conventional definition of topoi

In "Toward a Galoisian interpretation of homotopy theory" (2000), B. Toën wrote: Pour expliquer notre point de vue sur la notion de champs rappelons une construction (non conventionnelle) du topos de …
user234212323's user avatar
7 votes
2 answers
319 views

Indexing categories of derivators

It is not clear to me the role of the domain and target in the definition of prederivators. For instance, the classical references put the domain as $\mathit{Dia}$, others as $\mathit{Cat}$ itself. So …
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6 votes

Topos-theoretic Galois theory

Maybe you would like to see the thesis of O. Leroy, Groupoïde fondamental et théorème de Van Kampen en théorie des topos, available from https://plmbox.math.cnrs.fr/f/7ffa366379144dd4bacc/?dl=1 — the …
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5 votes
1 answer
278 views

Axioms of derivators

I would like to enter the world of derivators. We can find a little history here and there about the limitations of triangulated categories and the motivation to enhance them, but also to compute homo …
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3 votes

Making the étale topos construction a fully faithful 2-functor from schemes to Grothendieck ...

Take a look at the paper of Barwick, Glasman and Haine (https://arxiv.org/pdf/1807.03281.pdf). In particular the section "Exodromy for schemes & the Reconstruction Theorem".
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3 votes
0 answers
184 views

The site and the space

There is a (seemingly simple) statement in the literature on sheaf theory, namely, If $E$ is the site of opens of a topological space $X$, the notion of sheaf over $X$ coincides with that of sheaf of …
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3 votes
4 answers
534 views

Phenomena of topos

These days I am wandering on a wild adventure in an incredible but intimidating land. Fortunately, I could find a guide to some animals of this land Phenomena of gerbes But someone said to me that thi …
1 vote
1 answer
146 views

"Variable and fixed" in categories

We often find in Grothendieck terminology the words variable and fixed (or absolute). For example in SGA 4 studies variable topological spaces, groups, and categories as examples of morphisms of topos …
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1 vote
0 answers
212 views

Kan extensions in Grothendieck school

Considering both the ubiquity of Kan extensions in category theory (as MacLane stated, 'The notion of Kan extensions subsumes all the other fundamental concepts of category theory.'), its early introd …
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1 vote
0 answers
49 views

Defining properties of categories out of an indicial category

$\newcommand{\Hom}{\operatorname{Hom}}$Suppose we want to define the category of arrows of $S$. Below are two forms of doing it. Definition 1: If $D$ is of the following type: $\bullet \to \bullet$, …
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0 votes

Grothendieck's manuscript on topology

There is an article where you can find some ideas about this. Towards a new geometry of forms In: The notion of space in Grothendieck: from schemes to a geometry of forms, John Alexander Cruz Morale …