Introduction to Representation Theory
《Introduction to Representation Theory》 · 第 62 页 · Section 4.3「Examples」，例 (1)（省略中间关于共轭类计数的句子）
(1) Finite abelian groups $G=\mathbb Z_{n_1}\times\cdots\times\mathbb Z_{n_k}$. Let $G^\vee$ be the set of irreducible representations of $G$. […] Recall that all irreducible representations over $\mathbb C$ (and algebraically closed fields in general) of commutative algebras and groups are $1$-dimensional. Thus, $G^\vee$ is an abelian group: if $\rho_1,\rho_2:G\to\mathbb C^\times$ are irreducible representations, then so are the representations $\rho_1(g)\rho_2(g)$ and $\rho_1(g)^{-1}$. The group $G^\vee$ is called the dual group or character group of $G$.