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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.

4 votes
Accepted

Can Reedy cofibrations be monomorphisms?

I believe what you are after is the notion of "elegant Reedy category" This sort of things isn't true for a general Reedy category, but for an elegant one $R$ (see the link for the definition) if $\ma …
Simon Henry's user avatar
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8 votes
0 answers
232 views

Fibrations of the injective model structure on G-simplicial sets

Let $G$ be a discrete group. Consider the category of $G$-simplicial sets endowed with the injective model structure, i.e. cofibrations are the injective maps and weak equivalences are the maps which …
Simon Henry's user avatar
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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 …
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7 votes
Accepted

Almost combinatorial accessible model categories

Actually, you can, and you don't need accessibility (local presentability of the underlying category is enough). Under your assumption, for each $i:A \to B$ a generating cofibration, take $B \coprod_A …
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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
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1 vote
Accepted

Does a homotopy sheaf functor commute with group completion

I'm still confused by the question when $n>0$: $\pi_n^{\tau} X $ are already groups, so applying the group completion functor do not do anything to them, and, even in the catagory of spaces, I have ne …
Simon Henry's user avatar
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5 votes
Accepted

Is there a "geometric definition" of globular $\infty$-groupoids/categories?

In short there isn't: the problem is that if you just have globular sets - and if you want $k$-cells to model $k$-arrows following the globular structure - then globular sets have no way of expressing …
Simon Henry's user avatar
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13 votes
0 answers
477 views

Examples of non-proper model structure

I have recently been thinking about left and right semi-model categories and in which case they can be promoted to Quillen model structure, and I have come to the conclusion that that absolutely all t …
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13 votes

Correspondence between classes of model categories and classes of $\infty$-categories

Regarding (1) : A) Every model category has an associated $\infty$-category, obtained for example by taking the Dwyer-Kan localization at the class of all equivalence, (But there are other more expli …
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9 votes
0 answers
163 views

Proper model category for "categories with finite limits"

I'm looking for a Quillen model category which model the $2$-category of 'small category with finite limits (and functors between them preserving finite limits)': Left proper, right proper, Enriched …
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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 …
Simon Henry's user avatar
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10 votes

The cofibration/fibration $\leftrightarrow$ epi/mono confusion

This is probably not a full answer to your question, but I think it is a remark worth to make: It is actually a couple of remarks: 1)If you have a weak factorization system where either the left cla …
Simon Henry's user avatar
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2 votes
Accepted

Does the monoidal structure on semisimplicial sets preserve fibrant objects?

It is not the case: the terminal semi-simplicial set $1$ is obviously fibrant but as I will show below the geometric product $1 \otimes 1$ is not fibrant. 1) What does $1 \otimes 1$ look like ? So, $1 …
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7 votes

What are the advantages of simplicial model categories over non-simplicial ones?

I believe the main reasons enriched model category are simpler boils down to: Tensoring and co-tensoring by $\Delta[1]$ gives very well behaved path objects and cylinder objects adjoint to each other …
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6 votes
1 answer
260 views

Site dependance of the Cech weak equivalences on simplicial sheaves

Let $\mathcal{T}= sh(C,J)$ a Grothendieck topos of sheaves over a (ordinary) site. One endows the category of simplicial presheaves over $C$ with the "Rezk-Lurie" model structure: that is we start wi …
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