# Characteristic of Division Ring is Zero or Prime

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## Theorem

Let $\struct {D, +, \circ}$ be a division ring.

Let $\map {\operatorname {Char} } D$ be the characteristic of $D$.

Then $\map {\operatorname {Char} } D$ is either $0$ or a prime number.

## Proof

By definition, a division ring has no proper zero divisors.

If $\struct {D, +, \circ}$ is finite, then from Characteristic of Finite Ring with No Zero Divisors, $\map {\operatorname {Char} } D$ is prime.

On the other hand, suppose $\struct {D, +, \circ}$ is not finite.

Then there are no $x, y \in D, x \ne 0 \ne y$ such that $x + y = 0$.

Thus it follows that $\map {\operatorname {Char} } D$ is zero.

$\blacksquare$

## Sources

- 1965: Seth Warner:
*Modern Algebra*... (previous) ... (next): $\S 24$