Algebraic Number Theory
《Algebraic Number Theory》 · 第 366 页 · Chapter VI，Section 1「Ideles and Idele Classes」
For all modules $\mathfrak m$ of an arbitrary number field $K$, there will be Galois extensions $K^{\mathfrak m}/K$ generalizing the cyclotomic fields: the so-called ray class fields, which satisfy canonically $G(K^{\mathfrak m}/K)\simeq C_K/C_K^{\mathfrak m}$.