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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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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, …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar
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 …
Dmitri Pavlov's user avatar

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