Number Fields
《Number Fields》 · 第 12 页 · Chapter 2「Number Fields and Number Rings」
This result shows that the set of algebraic integers in $\mathbb C$ is a ring, which we will denote by the symbol $A$. In particular $A\cap K$ is a subring of $K$ for any number field $K$. We will refer to $A\cap K$ as the number ring corresponding to the number field $K$.