An **exceptional subgroup** of $\GL_2(\F_p)$ does not contain $\SL_2(\F_p)$ and is not contained in a Borel subgroup or in the normalizer of a Cartan subgroup.

Exceptional subgroups are classified according to their image in $\PGL_2(\F_p)$, which must be isomorphic to one of the alternating groups $A_4$ or $A_5$, or to the symmetric group $S_4$. These groups are labelled using identifiers containing one of the strings **A4**, **A5**, **S4**, as described in [MR:3482279] .

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- Review status: beta
- Last edited by Andrew Sutherland on 2017-03-16 15:21:09

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