Class Field Theory
《Class Field Theory》 · 第 11–12 页 · Section 1.2.6「The Heisenberg Group」，式 (1.13) 及跨页定义句
The set of all $3\times3$ real matrices $A$ of the form $A=\begin{pmatrix}1&a&b\\0&1&c\\0&0&1\end{pmatrix}$, where $a$, $b$, and $c$ are arbitrary real numbers, is the Heisenberg group.