The nine model category structures on the category of sets

Fuente: arXiv
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Main Authors: Antolín-Camarena, Omar, Barthel, Tobias
Format: Preprint
Published: 2025
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author Antolín-Camarena, Omar
Barthel, Tobias
author_facet Antolín-Camarena, Omar
Barthel, Tobias
contents We give a proof of the folklore theorem, attributed to Goodwillie, that there are precisely nine model structures on the category $\mathsf{Set}$ of sets. This result is deduced from a complete study of lifting problems and the ensuing classification of all weak factorization systems on $\mathsf{Set}$. Moreover, we determine the Quillen equivalences between these model structures and exhibit an explicit example of equivalent model structures that cannot be realized by a single Quillen adjunction.
format Preprint
id arxiv_https___arxiv_org_abs_2508_15731
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle The nine model category structures on the category of sets
Antolín-Camarena, Omar
Barthel, Tobias
Category Theory
Algebraic Topology
Combinatorics
We give a proof of the folklore theorem, attributed to Goodwillie, that there are precisely nine model structures on the category $\mathsf{Set}$ of sets. This result is deduced from a complete study of lifting problems and the ensuing classification of all weak factorization systems on $\mathsf{Set}$. Moreover, we determine the Quillen equivalences between these model structures and exhibit an explicit example of equivalent model structures that cannot be realized by a single Quillen adjunction.
title The nine model category structures on the category of sets
topic Category Theory
Algebraic Topology
Combinatorics
url https://arxiv.org/abs/2508.15731