Law of Division

Theorem
Let $\mathbb F$ denote one of the following number systems:


 * rational numbers $\Q$
 * real numbers $\R$
 * complex numbers $\C$

Let $a, b \in \mathbb F$ such that $a \ne 0$.

Then there exists a unique $x$ such that:
 * $a x = b$

$x$ is then defined and denoted:
 * $x := b / a$