# Correspondence Theorem for Localizations of Rings

## Theorem

Let $A$ be a commutative ring with unity.

Let $S\subseteq A$ be a multiplicatively closed subset.

Let $A \overset \iota \to A_S$ be the localization at $S$.

Let $I$ be the set of saturated ideals of $A$ by $S$.

Let $J$ be the set of ideals of $A_S$.

### Bijection

The direct image mapping $\iota^\to$ and the inverse image mapping $\iota^\gets$ induce reverse bijections between $I$ and $J$, specifically:

- For every ideal $\mathfrak a \in I$, its image $\iota^{\to}(\mathfrak a) = \iota(\mathfrak a) \in J$.
- For every ideal $\mathfrak b \in J$, its preimage $\iota^{\gets}(\mathfrak b) = \iota^{-1}(\mathfrak b) \in I$.
- The restrictions $\iota^\to : I \to J$ and $\iota^\gets : J \to I$ are reverse bijections.

### Prime ideals

Let $\mathfrak p \subseteq A$ be an ideal.

The following are equivalent:

- $\mathfrak p$ is a prime ideal of $A$ disjoint from $S$.
- $\mathfrak p$ is a prime ideal of $A$ saturated by $S$.
- $\iota(\mathfrak p)$ is a prime ideal of $A_S$.

### Open embedding of prime spectrum

The induced map on spectra $\operatorname{Spec} \iota : \operatorname{Spec} A_S \to \operatorname{Spec} A$ is a topological open embedding.