Let $\mathbb{N}$ be the D225: Set of natural numbers such that

(i)	$+ : \mathbb{N} \times \mathbb{N} \to \mathbb{N}$ is the D637: Natural number addition operation
(ii)	$$\begin{equation} {\sim} : = \left\{ ((a, b), (c, d)) \in \mathbb{N}^2 \times \mathbb{N}^2 : a + d = b + c \right\} \end{equation}$$

The set of integers is the D180: Quotient set $$\begin{equation} \mathbb{Z} : = \mathbb{N}^2 / {\sim} \end{equation}$$