Real Number Line is Complete Metric Space

Theorem
The real number line $\R$ with the usual (Euclidean) metric forms a complete metric space.

Proof
From Real Number Line is Metric Space, the distance function defined as $\map d {x, y} = \size {x - y}$ is a metric on $\R$.

It remains to be shown that the metric space $\struct {\R, d}$ is complete.

By definition, this is done by demonstrating that every Cauchy sequence of real numbers has a limit.

This is demonstrated in Cauchy's Convergence Criterion.

Hence the result.