Rational Addition is Commutative

Theorem
The operation of addition on the set of rational numbers $\Q$ is commutative:


 * $\forall x, y \in \Q: x + y = y + x$

Proof
Follows directly from the definition of rational numbers as the field of quotients of the integral domain $\struct {\Z, +, \times}$ of integers.

So $\struct {\Q, +, \times}$ is a field, and therefore a priori $+$ is commutative on $\Q$.