Unity Divides All Elements

Theorem
Let $\left({D, +, \circ}\right)$ be an integral domain whose unity is $1_D$.

Then unity is a divisor of every element of $D$:
 * $\forall x \in D: 1_D \mathrel \backslash x$

Also:


 * $\forall x \in D: -1_D \mathrel \backslash x$