\begin{definition}[Definition:Distance/Points/Real Numbers]
Let $x, y \in \R$ be real numbers.
Let $\size {x - y}$ be the absolute value of $x - y$.
Then the function $d: \R^2 \to \R$:
:$\map d {x, y} = \size {x - y}$
is called the '''distance between $x$ and $y$'''.
\end{definition}