Real Number Line is Metric Space

Theorem
Let $$\R$$ be the set of all real numbers.

Let $$d: \R \times \R \to \R$$ be defined as:

$$d \left({x_1, x_2}\right) = \left|{x_1 - x_2}\right|$$, where $$\left|{x}\right|$$ is the absolute value of $$x$$.

Then $$d$$ is a metric on $$\R$$ and so $$\left({\R, d}\right)$$ is a metric space.

Proof
From the definition of absolute value:

$$\left|{x_1 - x_2}\right| = \sqrt {\left({x_1 - x_2}\right)^2}$$.

It is clear that this is the same as the euclidean metric, which is shown in Euclidean Metric is a Metric to be a metric.

As the real number line is a vector space, it follows that the real number line is a 1-dimensional Euclidean space.