# Trivial Ring is Commutative Ring

## Theorem

Let $\struct {R, +, \circ}$ be a trivial ring.

Then $\struct {R, +, \circ}$ is a commutative ring.

## Proof

First we need to show that a trivial ring is actually a ring in the first place.

Taking the ring axioms in turn:

### A: Addition forms a Group

$\struct {R, +}$ is a group:

This follows from the definition.

$\Box$

### M0: Closure of Ring Product

$\struct {R, \circ}$ is closed:

From Ring Product with Zero, we have $x \circ y = 0_R \in R$.

$\Box$

### M1: Associativity of Ring Product

$\circ$ is associative on $\struct {R, +, \circ}$:

$x \circ \paren {y \circ z} = 0_R = \paren {x \circ y} \circ z$

$\Box$

### D: Distributivity of Ring Product over Addition

$\circ$ distributes over $+$ in $\struct {R, +, \circ}$:

$x \circ \paren {y + z} = 0_R$ by definition.

Then:

 $\displaystyle x \circ y + x \circ z$ $=$ $\displaystyle 0_R + 0_R$ $\displaystyle$ $=$ $\displaystyle 0_R$ Definition of Ring Zero

and the same for $\paren {y + z} \circ x$.

$\Box$

### Commutative

From the definition of trivial ring:

$\forall x, y \in R: x \circ y = 0_R = y \circ x$

Hence its commutativity.

$\blacksquare$