# Definition:Real Interval/Definition 2

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## Definition

A **real interval** is a subset of $\R$ that is one of the following real interval types:

- closed bounded interval
- open bounded interval
- left half-open bounded interval
- right half-open bounded interval
- closed and bounded on the right, also known as a closed unbounded below real interval
- open and bounded on the right, also known as an open unbounded below real interval
- closed and bounded on the left, also known as a closed unbounded above real interval
- open and bounded on the left, also known as an open unbounded above real interval
- unbounded interval without endpoints

## Also see

## Sources

- 1975: W.A. Sutherland:
*Introduction to Metric and Topological Spaces*... (previous) ... (next): Notation and Terminology