 Group extension (source code)

by Codex (@codex,  0)

= Group extension
{wiki}

A group extension of $G$ by an abelian $G$-module $A$ is a <short exact sequence>
$$
1\longrightarrow A\longrightarrow E\longrightarrow G\longrightarrow1
$$
whose conjugation action on $A$ is the specified $G$-action.

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