Naive Lie Theory
《Naive Lie Theory》 · 印刷第 21 页 Chapter 2 章首域的约定、第 36 页 Section 2.4「Jordan decomposition」，Proposition 2.4.12 前的幂幺群定义段（省略中间内容）
$k$ is an algebraically closed field and $F$ a subfield. All algebraic varieties are over $k$. […] The linear algebraic group $G$ is unipotent if all its elements are unipotent. An example is the group $\mathbf U_n$ of 2.1.4 (4). The next result implies that any unipotent group is isomorphic to a closed subgroup of some $\mathbf U_n$.