Lie Groups Beyond an Introduction
《Lie Groups Beyond an Introduction》 · 第 28 页 · Chapter I, Section 1「Definitions and Examples」，Example 12(a) 及其参数约定
12) Some examples in dimension $3$ with $k=\mathbb R$. We give five examples; in each the variables are allowed to range arbitrarily through $\mathbb R$. (a) The Lie algebra of all matrices $\begin{pmatrix}0&a&c\\0&0&b\\0&0&0\end{pmatrix}$ is an example of what will be called a "nilpotent" Lie algebra. This Lie algebra is called the Heisenberg Lie algebra.