Local Fields
《Local Fields》 · 第 16 页 · Chapter I，Section 5「Norm and Trace」，定义段
For the integral closure $B$ of a Dedekind domain $A$ in a finite extension, the norm on ideal groups is defined on a prime ideal $\mathfrak P$ above $\mathfrak p$ by $N(\mathfrak P)=\mathfrak p^{f_{\mathfrak P}}$ and is extended multiplicatively.