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# Homology, Homotopy and Applications

## Volume 25 (2023)

### Number 1

### Koszul duality in higher topoi

Pages: 53 – 70

DOI: https://dx.doi.org/10.4310/HHA.2023.v25.n1.a3

#### Authors

#### Abstract

We show that there is an equivalence in any $n$-topos $\mathscr{X}$ between the pointed and $k$-connective objects of $\mathscr{X}$ and the $\mathbb{E}_k$-group objects of the $(n-k-1)$-truncation of $\mathscr{X}$. This recovers, up to equivalence of $\infty$-categories, some classical results regarding algebraic models for $k$-connective, $(n-1)$-coconnective homotopy types. Further, it extends those results to the case of sheaves of such homotopy types. We also show that for any pointed and $k$-connective object $X$ of $\mathscr{X}$ there is an equivalence between the $\infty$-category of modules in $\mathscr{X}$ over the associative algebra $\Omega^k X$, and the $\infty$-category of comodules in $\mathscr{X}$ for the cocommutative coalgebra $\Omega^{k-1} X$. All of these equivalences are given by truncations of Lurie’s $\infty$-categorical bar and cobar constructions, hence the terminology “Koszul duality.”

#### 2010 Mathematics Subject Classification

16T15, 18D35, 55U30

Copyright © 2023, Jonathan Beardsley and Maximilien Péroux. Permission to copy for private use granted.

Received 7 February 2021

Received revised 20 December 2021

Accepted 22 December 2021

Published 1 March 2023