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Part of higher category theory that for instance in Algebraic Topology enables us to capture finer homotopic distinctions. As in say Eilenberg-Maclane spaces.
8
votes
Accepted
Homotopy (co)limits in oo-categories vs model categories
The ∞-categorical limits (respectively colimits) are given by the right (respectively left) adjoint of the constant diagram functor $$C→C^I,$$
where $I$ is the indexing category and $C$ is the ∞-categ …
2
votes
Is there a shape-independent definition of (∞,1)-categories?
Yes. As shown in the paper The enriched Thomason model structure on 2-categories, the category of (strict) 2-categories can be equipped with a model structure that makes it Quillen equivalent to the …
3
votes
Accepted
Simplicial objects in quasicategory which come from homotopy coherent nerve
It is easy to construct counterexamples already for the full subcategory $\{[0],[1]\}⊂Δ$. The category $\cal C$ can be constructed by applying the nerve functor to hom-objects of a category $D$ enric …
5
votes
Model categories: "equivalence" of finite limits and finite colimits
The statement is false in its current form: there are left Quillen functors between stable model categories that do not preserve finite limits.
However, since ∞-categories are mentioned, presumably wh …
5
votes
Accepted
From the *usual* nerve of topological categories to $\infty$-categories
The answer to Question (ii) is positive. That is to say, there is a weak equivalences between the following functors from Segal topological categories to quasicategories: the composition of the singu …
3
votes
Accepted
A fiber-like method to show equivalence of infinity categories
An obvious necessary condition for $f$ to be a categorical equivalence is that $f$ is weakly equivalent to a (co)cartesian fibration of quasicategories, i.e., $f$ is an analogue of a Street fibration …
4
votes
Accepted
Homotopy totalization and chains - reference
The first part of the question was previously asked and answered here: Reference for homotopy colimit = total complex.
The second part can be easily reduced to the first part by rectifying homotopy co …
12
votes
Accepted
The derived category does not satisfy descent - example
Consider the canonical functor $H$ from the homotopy category of homotopy coherent descent data in the ∞-category of coherent sheaves
to the category of descent data in the derived category of coheren …
2
votes
Accepted
Homotopical properties of powersets of simplicial sets
The first question has a negative answer, given by the simplicial set $\def\Exi{{\sf Ex}^{\sf\infty}}X=\Exi Y$, where $Y$ is a simplicial set generated by vertices $a,b,b',c,c',d,d'$, 1-simplices $ab, …
5
votes
Accepted
HTT, Remark 4.2.4.5
As shown by Dwyer–Kan (Function complexes in homotopical algebra, Proposition 4.8), for a simplicial model category $A$, the simplicial category $A^\circ$ is Dwyer–Kan equivalent to the simplicial cat …
3
votes
Reference for the Brown representability theorem in the case of locally presentable (∞,1)-ca...
As pointed out to me by George Raptis, a detailed treatment of Brown representability for $(n,1)$-categories ($1≤n≤∞$), stable or not, is now available in
Hoang Kim Nguyen, George Raptis, Christoph S …
6
votes
Quillen pairs / $\infty$-adjunctions / adjunctions of homotopy categories
More precisely, let A,B be two simplicially enriched model categories, is it true that every adjoint pair of ∞-functors between A,B comes from a Quillen pair?
Assuming the model categories are combi …
18
votes
Accepted
When did the Joyal model structure on simplicial sets originate?
Here is what André Joyal wrote in an email to me:
No, I have not discovered the model structure for quasi-categories in the 1980's.
I became interested in quasi-categories (without the name) around 1 …
5
votes
Accepted
Derived functors out of an unbounded derived $\infty$-category
An account of derived functors between ∞-categories equipped with weak equivalences and fibrations can be found in Section 7.5 of Cisinski's Higher Categories and Homotopical Algebra. This setting is …
5
votes
Accepted
$\infty$-groupoid iff Kan condition
A good place to start is the following characterization of nerves of ordinary groupoids:
A category is a groupoid if and only if its nerve is a Kan complex.
Filling the outer horns is precisely what …