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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.
42
votes
Accepted
How should I think about presentable $\infty$-categories?
Presentable $\infty$-categories can be understood without every having to think about cardinals. An $\infty$-category is presentable iff it is equivalent to one of the form $\mathcal{P}(C,R)$, where
…
37
votes
Is there an accepted definition of $(\infty,\infty)$ category?
As you point out, there are "inclusion" functors $\mathrm{Cat}_n\to \mathrm{Cat}_{n+1}$. These inclusion functors admit both left and right adjoints (in the sense of functors between $(\infty,1)$-cat …
18
votes
Accepted
Are n-truncated quasicategories a model for n-categories?
Let $C$ be an $\infty$-category, and $n\geq -1$. The following are equivalent:
$C$ is $n$-truncated.
The $\infty$-groupoids $\def\Map{\operatorname{Map}}\Map(\Delta^0,C)$ and $\Map(\Delta^1,C)$ are …
12
votes
Accepted
Monomorphisms, epimorphisms, (co-)images and factorizations in $\infty$-categories
An $n$-monomorphism is a map $A\to B$ for which $Map(X,A)\to Map(X,B)$ has all homotopy fibers $n$-truncated, for all $X$; a space (=$\infty$-groupoid) is $n$-truncated if its homotopy groups all vani …
12
votes
The Yoneda Lemma for $(\infty,1)$-categories?
The Yoneda lemma is certainly true for $(\infty,1)$-categories, and I can give you a proof: if you let me choose the model of $(\infty,1)$-categories I use!
I'll take topological categories (=catego …
11
votes
What is higher equivariant homotopy?
I would also like to know the answer to your question. Since no one has given an answer yet, I'll speculate recklessly and irresponsibly on how this might work (by riffing off of the final paragraph …
8
votes
Accepted
Stable presentable categories as module categories
According to the abstract of http://arxiv.org/abs/math/0108143 (Schwede & Shipley, Classification of Stable Model Categories), they deal with the case of stable model categories (=stable presentable ( …
5
votes
Accepted
Presheaves on a complete Segal space
Yes. Let $W$ be a complete Segal space, thought of as a simplicial "space" $(W_q)$. The fibrant objects of your model category will be the fibrations $f:X\to W$ such that for each simplicial operato …
4
votes
Non-unique splittings of homotopy idempotents
The question "can a given homotopy idempotent admit multiple inequivalent coherentifications" ought to be approachable by the standard spectral sequence machinery, so let me try to do that. I'll more …
4
votes
Accepted
explicit description of the cosimplicial simplicial set $Q^{\bullet}$
Here is how I think about this; don't know if it will help.
Start with the straightening construction: this takes a map $f\colon X\to S$ of simplicial sets to a simplicial functor $\def\St{\mathrm{St …
4
votes
Accepted
Higher-dimensional version of the "Magic Cube Lemma" for homotopy pushouts/pullbacks
I don't think so. Take $n=2$, and consider a map $f\colon b\to a$ between objects of $\mathrm{Fun}(I^2, \mathcal{S})$. If $a$ and $b$ are pullback squares, then any map $f$ between them is relativel …
3
votes
n-truncation/n-connected factorization in an $\infty$-topoi
I think the point is that a map $f\colon A\to B$ in a slice
$\mathscr{C}_{/Y}$
is $k$-connected if and only if the underlying map in $\mathscr{C}$ is
$k$-connected, and this is supposed to be a formal …