Unity Divides All Elements/Proof 1

Proof
The element $1_D$ is the unity of $\left({D, +, \circ}\right)$, and so:
 * $1_D \in D: x = 1_D \circ x$

Similarly, from Product of Ring Negatives:


 * $-1_D \in D: x = \left({-1_D}\right) \circ \left({-x}\right)$

The result follows from the definition of divisor.