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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.

3 votes
Accepted

A distinguished triangle of mapping spectra arising from recollement

I'm going to do a proof assuming we are in a stable $\infty$-category (I'm pretty sure this is almost equivalent to your "sufficiently rich" situation anyway). In your case $F=j_!j^!$ and $G=i_*i^*$. …
Denis Nardin's user avatar
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6 votes

Geometric Meaning of Different K-theories

Fibrant replacement is essentially sheavification with respect to the corresponding topology. So étale K-theory is nothing more than the part of K-theory that satisfies étale descent. Concretely (and …
Denis Nardin's user avatar
  • 16.5k
4 votes
Accepted

Does the existence of a derived functor imply existence of model structure?

This is not quite the answer to your question as you pose it. I hope it will be useful anyway. By and large I am just expanding user337830 comments. Everything will use homological grading (what can I …
Denis Nardin's user avatar
  • 16.5k
8 votes
Accepted

Homotopy function complex for quasi-categories

Yes, you can compute the mapping spaces in ∞-categories by taking the biggest Kan subcomplex of the internal hom. The trick is not to use the Joyal model structure, but instead the model structure on …
Denis Nardin's user avatar
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3 votes
Accepted

Kan complexes and semigroups

(2) is true (and so (1) is false). To see it, note that every horn $\Lambda^n_i\to S$ to a constant simplicial set must be constant, and so it can be filled by the constant horn $\Delta^n\to S$. Equi …
Denis Nardin's user avatar
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33 votes
Accepted

Why is Voevodsky's motivic homotopy theory 'the right' approach?

(Don't be afraid about the word "$\infty$-category" here: they're just a convenient framework to do homotopy theory in). I'm going to try with a very naive answer, although I'm not sure I understan …
Denis Nardin's user avatar
  • 16.5k