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Homotopy theory, homological algebra, algebraic treatments of manifolds.

6 votes
Accepted

When does a cofibrantly generated model category have this factorization property?

I've encountered that condition a few time. Here is what I know about it: If that property is satisfied for a model category $M$ then the full subcategory $C$ of finite $I$-cell complex is itself a Br …
Simon Henry's user avatar
  • 42.4k
47 votes

What is the mistake in the proof of the Homotopy hypothesis by Kapranov and Voevodsky?

It's been more than a year and a half since I asked this question and I had a lot of thought about it so I decided I will post my own answer. First I entirely agree with Yonatan that the main problem …
LSpice's user avatar
  • 12.9k
106 votes
4 answers
13k views

What is the mistake in the proof of the Homotopy hypothesis by Kapranov and Voevodsky?

In 1991, Kapranov and Voevodsky published a proof of a now famously false result, roughly saying that the homotopy category of spaces is equivalent to the homotopy category of strict infinity categori …
18 votes

Why the sphere spectrum is more correct than $\mathbb{Z}$?

For this to work, it is best to identify connective spectrum with spaces equipped with a group-like $E_\infty$-algebra structure (these are equivalent). From this point of view: $\mathbb{Z}$ is the f …
Gro-Tsen's user avatar
  • 32.5k
11 votes
0 answers
219 views

On an Artin (?) subgroup of braid groups

While working on something apparently unrelated I encountered a "braid-like" group, which is a relatively geometric subgroup of a braid group and seems to be itself an Artin group. It seems like somet …
9 votes
0 answers
192 views

Every locally presentable $\infty$-category can be presented by a proper model category

Is there an argument in the litterature that show that every locally presentable $\infty$-category is equivalent to the localization of proper combinatorial Quillen model category ? Of course if one r …
13 votes

sSet-enriched categories, quasi-categories and the model-independent theory

This has not been done, and there are good reasons for it: While $sSet$-enriched categories are indeed very good to easily get examples of $\infty$-categories, they are very bad at understanding what …
Simon Henry's user avatar
  • 42.4k
8 votes
Accepted

Is the suspension of a finite fibration again finite?

Assuming you work with unpointed spaces (but the example can easily be adapted to the pointed case) the map $1 \to 2$ gives a counterexample : its fiber are $1$ and $\varnothing$ so they are both fini …
Simon Henry's user avatar
  • 42.4k
8 votes
2 answers
329 views

example of "really" non-existent transferred model structure

I am looking for an example where a transferred model structure fails to exist, even if one is willing to work with semi-model category. But let me be more precise: Let's say I have a combinatorial mo …
15 votes
1 answer
494 views

On diagrams in model categories and rectification

For a model category $C$, I'm denoting $h_\infty(C)$ the associated $\infty$-category (for example its Dwyer-Kan localization at weak equivalences, or if $C$ is simplicial the simplicial nerve of the …
13 votes
Accepted

Alternatives to "Sketches of an Elephant" Volume 3

As I said in the comment, this would involve a very large number of different references! (almost one by subsection...) But to some extent, contributors to the nLab already started doing that and it i …
Joald's user avatar
  • 103
7 votes
1 answer
295 views

Is the canonical model structure on strict $\infty$-Cat left proper?

Is the canonical (or Folk) model structure on the category of (strict) $\infty$-categories as constructed by Lafont, Métayer and Worytkiewicz in A folk model structure on omega-cat left proper ? All i …
7 votes
1 answer
230 views

Free extension of algebra for an operad

I fix $C$ a symmetric monoidal model category (with a cofibrant unit if it helps). I'm assuming that it is closed, or at least that the tensor product commutes to colimits in each variable. If $X$ is …
6 votes
2 answers
465 views

CW-presentation of configurations of points in plane and space

I know from the the theory of Artin groups that, as the $K(\pi,1)$ conjecture is known for Braids group, that using Salvetti complexes we have a fairly explicit finite CW-complex presentation of the c …
3 votes
Accepted

Euclidean model structure on multipointed $d$-spaces

As mentioned by David White in the comment, I've recently proved that left induced model structure exists (without any kind of large cardinal axiom) for any "tractable" class of cofibrations on a loc …
Simon Henry's user avatar
  • 42.4k

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