《Algebra》
· 第 430 页 · Chapter IX，Section 2，Definition 2.11
An element $a$ of a ring $R$ is nilpotent if $a^n=0$ for some positive integer $n$. A (left, right, two-sided) ideal $I$ of $R$ is nil if every element of $I$ is nilpotent; $I$ is nilpotent if $I^n=0$ for some integer $n$.
