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For questions involving one or more categorical dimensions, or involving homotopy coherent categorical structures.
5
votes
2-groups are to crossed modules as 2-categories are to...?
I think Theo's "no go" is exactly right. Here is an example which might make things easier to understand: Let X be any category. I am going to construct an interesting 2-category with one object which …
7
votes
0
answers
226
views
Good Internal Hom for Weak Complicial Sets?
So I am trying to learn a bit more about Dominic Verity's model of higher categories, namely weak complicial sets. The underlying object is a stratified simplicial set which satisfies a sort of inner …
2
votes
Accepted
$\Omega$ and $B$ as adjoints between symmetric monoidal $(\infty,n)$- and $(\infty,n-1)$-cat...
I assume you meant "symmetric monoidal functors".
Yes, this seems to hold. By your description you have constructed maps:
$$ \eta: \mathcal{C} \cong \Omega B \mathcal{C}$$
$$ \varepsilon: B \Omega \ …
4
votes
Accepted
How strict can I be in the definition of "2-group"?
You can always do this. Take any $b$ and define $d = p_2 b$. Then $b' = (p_1, d)$ is equivalent to the original $b$. To see this note that
$$(p_1, m) \circ b = (p_1b, m \circ (p_1 b, d)) \simeq id = …
26
votes
Accepted
Is every category a localization of a poset?
Yes, this is true. It follows form the work of Barwick and Kan on relative categories as a model for $\infty$-categories.
The idea is similar to how Thomason's work shows that every homotopy type can …
22
votes
2
answers
2k
views
Lax Functors and Equivalence of Bicategories?
Lax functors of bicategories were introduced at the very inception of bicategories, and I'm trying to get a better feel for them. They are the same as ordinary 2-functors, but you only require the exi …
62
votes
7
answers
6k
views
Are higher categories useful?
Of course, personally, I think the answer is a big Yes!
However once, a while ago, while giving a talk about higher category theory, I was asked a question about whether higher category theory was us …
2
votes
1
answer
341
views
Are lax functor categories into a cartesian closed 2-category cartesian closed?
Suppose that $C$ is a complete closed monoidal category and $I$ is any small category. Then the functor category $Fun(I,C)$ is again a closed monoidal category with the pointwise tensor product $F \ot …
4
votes
Accepted
An explicit expression for the naturality of the Serre automorphism in the bicategory of alg...
We will use the fact that $M$ is invertible. Let ${}_BN_A$ be an inverse to $M$. Thus we have isomorphisms
$${}_AM \otimes_B N_A \cong {}_AA_A$$
and
$${}_BN \otimes_A M_B \cong {}_BB_B$$
If we make th …
11
votes
Accepted
Do Homotopy Fully Faithful Functors Push-out?
The answer is yes, fully-faithful functors are stable under co-base change.
This is a model independent statement and so we can in particular take $\infty$-category to mean Segal categories. Then t …
7
votes
Accepted
Is there a model-independent characterization of the gaunt strict $n$-categories amongst the...
Alexander Campbell's guess is correct.
Here is a reference.
Lemma 10.2 of this paper
Clark Barwick, Christopher Schommer-Pries, On the Unicity of the Homotopy Theory of Higher Categories, arXiv:1112. …
73
votes
Do we still need model categories?
Here are some rough analogies:
Model Category :: $(\infty, 1)$-category
Basis :: Vector space
Local coordinates :: Manifold
I especially like the last one. When you do, say, differential geometry …
38
votes
4
answers
5k
views
Invertible matrices of natural numbers are permutations... why?
I have heard the following statement several times and I suspect that there is an easy and elegant proof of this fact which I am just not seeing.
Question: Why is it true that an invertible nxn …
2
votes
Accepted
Are hammock localizations locally truncated?
Your calculation is correct. For every two objects $X, Y \in \mathcal{C}$, the hom space $L^H\mathcal{C}(X,Y)$ has the right lifting property against $\partial \Delta^n \to \Delta^n$ for $n \geq 3$.
F …
8
votes
0
answers
315
views
A model category for E-infty algebras in a non-monoidal model category?
Given a suitable nice symmetric monoidal category $C$, symmetric monoidally enriched, tensored, and cotensored over a symmetric monoidal category $S$, and an operad $\mathcal{O}$ in $S$, we can consid …