# Closed Real Interval is Compact

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## Contents

## Theorem

Let $\R$ be the real number line considered as an Euclidean space.

Let $I = \left[{a \,.\,.\, b}\right]$ be a closed real interval.

Then $I$ is compact.

## Proof

From Closed Real Interval is Closed Set, $I$ is a closed set of $\R$.

From Real Interval is Bounded in Real Numbers, $I$ is bounded in $\R$.

The result follows by definition of compact.

$\blacksquare$

## Also see

## Sources

- 1967: George McCarty:
*Topology: An Introduction with Application to Topological Groups*... (previous) ... (next): $\text{III}$: Compactness