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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.

30 votes
1 answer
1k views

Homotopical algebra is not concrete

There is this old result by Freyd that "homotopy is not concrete": Freyd, Peter. "Homotopy is not concrete." The Steenrod Algebra and Its Applications: A Conference to Celebrate NE Steenrod's Six …
fosco's user avatar
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8 votes
2 answers
349 views

Co/fibrant replacements via coend calculus

In the paper Cordier, Jean-Marc, and Timothy Porter. "Homotopy coherent category theory." Transactions of the American Mathematical Society 349.1 (1997): 1-54. the authors define a notion of coh …
fosco's user avatar
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7 votes
3 answers
905 views

A fibrant-objects structure on Top

(Sorry for the crossposting, but I'm really interested in this question). One can define (Paragraph 1.5, page 10) a fibrant-object structure on a suitable cartesian closed category of topological spac …
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6 votes
0 answers
147 views

Model structures on varieties of algebras

I say that a category of (say) algebras for a monad[¹] $\text{Alg}(\mathbb T)$ is "uninteresting" if the only model structures on $\text{Alg}(\mathbb T)$ result as transfer of the nine model structure …
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6 votes
2 answers
334 views

Model bicategories

From a conceptual point of view, the notion of a "model bicategory" is clear: a complete, cocomplete bicategory where there are two "very weak" factorization systems, where the commutativity of the sq …
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4 votes
0 answers
118 views

Conditions on a Quillen functor so that its comonad is homotopy-full

I am looking for an answer to the following question: Let $F : {\cal C} \to {\cal D}$ be a left Quillen functor between combinatorial model categories; let $\tilde F \dashv \tilde G$ be the induced a …
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1 vote
0 answers
431 views

Homotopical Galois theory of coverings

In the hope this won't turn into a trivial problem (I couldn't find a similar discussion here), here's my question. I'm studying a little homotopical algebra in this article by Brown. You can easily …
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