Binary relations

In this chapter we study examples involving the classical sets of number, namely the sets $\mathbb{N}$ (natural numbers), $\vert Z$ (integres), $\mathbb{Q}$ (rational numbers) and $\mathbb{R}$ (real numbers). We rely on their intuitive knowledge; precise definitions for $\mathbb{N}$, $\mathbb{Z}$ and $\mathbb{Q}$ will be given in Chapter 6. For $\mathbb{R}$, this task is beyond the scope of these notes.