Naive Lie Theory
《Naive Lie Theory》 · 印刷第 21 页 Chapter 2 章首域的约定、第 22 页 2.1.4(1) 加法群记号、第 51 页 Section 3.4「Elementary unipotent groups」，3.4.1 的向量群定义句（省略中间内容）
$k$ is an algebraically closed field and $F$ a subfield. All algebraic varieties are over $k$. […] (1) $G=\mathbf A^1=k$ with addition as group operation. This defines a linear algebraic group, with $A=k[T]$. […] We denote this algebraic group by $\mathbf G_a$; it is the additive group. […] $G$ is a vector group if it is isomorphic to some $\mathbf G_a^n$.