Abstract Algebra
《Abstract Algebra》 · 第 846 页 · Chapter 18，Section 18.1，Example (11)（省略同段的另一子模）
If $V=FG$ is the regular representation of $G$ described in Example 2 above, then $V$ has $FG$-submodules of dimensions $1$ and $|G|-1$ as in the preceding example: […] $I=\{a_1g_1+a_2g_2+\cdots+a_ng_n\mid a_1+a_2+\cdots+a_n=0\}$. […] The ideal $I$ is called the augmentation ideal of $FG$ […].