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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

Compact objects in the $\infty$-category presented by a simplicial model category

If $X$ is such that $X \times \Delta^n$ is compact for every $n$ then yes. This happens, for example, if the cotensor functor $(-)^{\Delta^n}$ preserves filtered colimits, a condition which is quite c …
Yonatan Harpaz's user avatar
6 votes

Theorem 2.1.2.2 Higher Topos Theory

I think what Lurie might have meant when he wrote "It is easy to see that $St_{\phi}$ preserves cofibrations" in the proof of Theorem 2.2.1.2, is that it is easy to see it if you take into account the …
Yonatan Harpaz's user avatar
5 votes
Accepted

Proposition in HTT on cofibrations of categories

You can argue as follows. Suppose that $g: D \to D'$ is a retract of $f: C \to C'$ (in the category of $S$-enriched categories) via maps $D \stackrel{i}{\to} C \stackrel{r}{\to} D$ and $D' \stackrel{i …
Yonatan Harpaz's user avatar
8 votes
Accepted

Quillen equivalence, fibrant objects

Here is a counter-example to the dual assertion (so that you can get a counter-example to your original question by taking the opposite model categories). Consider the category ${\rm Set_\Delta}$ of s …
Yonatan Harpaz's user avatar
1 vote

Deriving the functor $ \int_{\Gamma} F(-,-)$

The answer is no in this generality, but I do not know what happens specifically for ${\bf dgCat}$ and ${\bf dgFun}$. For convenience, let me construct a counter-example to the dual of your question, …
Yonatan Harpaz's user avatar
9 votes
Accepted

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

The (epi,mono) factorization system in Sets is part of a model structure on Sets whose weak equivalences are the epis, fibrations are monos and cofibrations are everything. This is a model for the hom …
Yonatan Harpaz's user avatar
5 votes

Property-like structure in a model category

Specifically for the case of quasi-categories (or any other model for $\infty$-categories) the following observation can be useful: suppose that $f: {\cal C} \to {\cal D}$ is a map of quasi-categories …
Yonatan Harpaz's user avatar
5 votes

Gray product on $(\infty,2)$-categories

For question (2), there is actually a left Quillen bifunctor $$ \times_{\mathrm{gr}}: \mathrm{Set}_\Delta^{\mathrm{sc}} \times \mathrm{Set}_\Delta^{\mathrm{sc}} \to \mathrm{Set}_\Delta^{\mathrm{sc}} $ …
Yonatan Harpaz's user avatar
4 votes

Why is every object cofibrant in an excellent model category?

I am now under the impression that it is simply not true that in an excellent model category every object is cofibrant. Let $\mathbf{S}$ be an excellent model category in which the monoidal structure …
Yonatan Harpaz's user avatar
7 votes
Accepted

Methods for defining/calculating homotopy limits of quasicategories

When working with quasi-categories, it is often more convenient (and more compatible with existing machinery) not to work with actual strict diagrams of quasi-categories but rather with coCartesian fi …
Yonatan Harpaz's user avatar
14 votes
1 answer
485 views

Why is every object cofibrant in an excellent model category?

In Appendix A.3 of the book higher topos theory appears the notion of an excellent model category (see Definition A.3.2.16). The main feature of this notion is that when $\mathbf{S}$ is an excellent m …
Yonatan Harpaz's user avatar
7 votes

From relative categories to marked simplicial sets

Concerning the first question: the simplicial localization functor $L^H$ induces an equivalence from the relative category of small relative categories to the relative category of small simplicial cat …
Yonatan Harpaz's user avatar