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A model category is a category equipped with notions of weak equivalences, fibrations and cofibrations allowing to run arguments similar to those of classical homotopy theory.

2 votes
1 answer
215 views

In what generality does the following statement hold: A fibration is acyclic if and only if ...

This may not be precise enough for MO, but I'll give it a go. Let $M$ be a symmetric closed monoidal model category with unit $u\in Ob(M)$. We define the vertices of an object $A$ to be points $x\in …
Harry Gindi's user avatar
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4 votes
0 answers
1k views

When are "diagrams of cofibrations" projectively cofibrant?

Let $P$ be a small category, and let $F:P\to M$ be a diagram in a left-proper combinatorial model category $M$. We say that $F$ is a diagram of cofibrations if for every object $p\in P$, $F(p)$ is co …
Harry Gindi's user avatar
  • 19.6k
3 votes
2 answers
269 views

Excellent monoidal model categories admit enriched fibrant replacement functors?

Let $\mathbf{S}$ be an excellent model category in which all objects are cofibrant, viewed as an $\mathbf{S}$-enriched category by its canonical self-enrichment. Then we know that there is an obvious …
Harry Gindi's user avatar
  • 19.6k
13 votes
3 answers
3k views

What is the "universal problem" that motivates the definition of homotopy limits/colimits (a...

The ordinary notions of limit and colimit are universal solutions to a problem, specifically, finding terminal/initial objects in slice/coslice categories. In the context of homotopy right Kan extens …
Harry Gindi's user avatar
  • 19.6k
6 votes
1 answer
192 views

Inductive folk model structure on strict ω-categories

There is a paper of Lafont, Metayer, and Worytkiewicz [1] that constructs a model structure on the category of strict $\omega$-categories that they call the folk model structure. This model structure …
Harry Gindi's user avatar
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7 votes
0 answers
248 views

Product-preserving fibrant replacement functor for the Joyal model structure

There are a few fibrant replacement functors for the Quillen model structure on simplicial sets that preserve finite cartesian products, namely $\operatorname{Ex}^\infty$ and $\operatorname{Sing}(|\cd …
Harry Gindi's user avatar
  • 19.6k
8 votes
0 answers
119 views

Explicit data for $E_n$-monoidal model and simplicial categories

The definition of a monoidal model category requires that the tensor product is biclosed (such is needed to ensure that the tensor product is derivable in both variables). Obviously, in the situation …
Harry Gindi's user avatar
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5 votes
0 answers
93 views

Classification of combinatorial model categories presentable by simplicial presheaves on a R...

Dan Dugger proved that every combinatorial model category can be obtained up to Quillen equivalence as the localization of a model structure on simplicial presheaves on a small category $C$. Is there …
Harry Gindi's user avatar
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4 votes
1 answer
310 views

Model category with formally smooth morphisms as fibrations?

Let's view the category of algebraic spaces as a full subcategory of the category of "spaces" over the opposite category of commutative rings, that is, the category of sheaves on $CRing^{op}$ in the é …
Harry Gindi's user avatar
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1 vote
1 answer
364 views

Analogs of left, right, inner, and Kan fibrations in CGWH

It is a theorem that the category of compactly generated weakly Hausdorff (CGWH) spaces is Quillen equivalent to the category of simplicial sets with the Kan model structure. However, I know next to …
Harry Gindi's user avatar
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3 votes
1 answer
458 views

Slick verification of the model category axioms for Spaces and SSets with the q-model struct...

We choose our category of spaces to be compactly generated weak Hausdorff spaces for convenience, denoted $CGWH$. Questions: 1.) Is there any sort of slick argument to verify that CGWH with the Qu …
Harry Gindi's user avatar
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8 votes
0 answers
667 views

An Ex functor for the contravariant homotopy structure

I'm going to slack on the background and get to the point: Is there a good notion of an $Sd/Ex$ adjunction for $sSet/S$ equipped with the contravariant model structure (cofibrations are monomorphisms …
Harry Gindi's user avatar
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12 votes
1 answer
1k views

Is the simplicial completion of a localizer always a bousfield localization of the injective...

Background Recall (from Cisinski's Astérisque volume 308) that given a small category $A$, we define an $A$-localizer to be a class $W$ of morphisms of $\mathrm{Psh}(A)$ satisfying the following axio …
Harry Gindi's user avatar
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14 votes
1 answer
494 views

Weak complicial sets: Are the morphisms too strict?

In Verity's first paper on weak complicial sets, he shows that every strict complicial set is a weak complicial set. He also showed in an earlier paper that the full subcategory of stratified simplic …
Harry Gindi's user avatar
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9 votes
1 answer
1k views

Fibered/cofibered higher categories, relative model structures, slicing, and (∞,2)-category ...

Jacob Lurie defined a model structure on the category of marked simplicial sets sliced over a fixed simplicial set $S$ called the cartesian model structure. (For a definition, see here or HTT Ch.3.1) …
Harry Gindi's user avatar
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