# Contents

## Definition

Let $C$ be a groupoid.

A permutation representation of $C$ is a representation of $C$ on Set, i.e. a functor $C \to \Set$.

A linear permutation representation is a functor $C \to$ Vect that factors through a permutation representation via the free functor $k^{|-|}\colon Set \to Vect$ which sends a set to the vector space for which this set is a basis.

###### Warning

In the usual literature of representation theory, “linear permutaton representations” are just called “permutation representations”.

## Examples

Notably for $C = \mathbf{B}G$ the delooping groupoid of a group $G$, a permutation representation $\mathbf{B}G \to Set$ is a set equipped with a $G$-action.

The category

$Rep(G, Set) \simeq PSh(B G)$

is the classifying topos for the group $G$.

Revised on December 12, 2011 23:05:13 by Urs Schreiber (82.169.65.155)