# nLab local integral domain

### Context

#### Algebra

higher algebra

universal algebra

# Contents

## Definition

A local integral domain is a commutative ring which is both a local ring and a integral domain, hence a commutative ring such that:

• The ring is nontrivial $0 \neq 1$;

• if the sum of two elements $x + y$ is equal to $1$, then $x$ is invertible or $y$ is invertible;

• If the product of two elements $x \cdot y$ is equal to $0$, then $x = 0$ or $y = 0$.

## Examples

• Every field is a local integral domain which is also a Artinian ring.

• Given a field $K$, the ring of power series $K[[x]]$ is a local integral domain which is not a field.

• In general, given a local integral domain $R$, the ring of power series $R[[x]]$ is a local integral domain.

• Every discrete valuation ring is a local integral domain with a Dedekind-Hasse norm.

• Every finite local integral domain is a finite field.

## Properties

Unlike the theory of Heyting fields, the theory of local integral domains is a coherent theory. It is the condition that a local integral domain is an Artinian ring that fails in coherent logic, since it relies on either negation to refer to non-invertible elements (see Artinian local ring), proper ideals/maximal ideals, or the natural numbers to refer to the descending chain condition. Even if one has the natural numbers around to define a dependent sequence of monomorphisms for the descending chain condition, such as working internally in an arithmetic pretopos, it is not necessarily the case that every such Artinian local ring has a maximal ideal or that Nakayama's lemma holds in coherent logic.

While every ring homomorphism between fields is an injection, it is not the case that every ring homomorphism between local integral domains is an injection. The ring homomorphism which takes a local integral domain to its residue field is an injection if and only if the local integral domain is already a field.