The open sets of $\reals$ (the unions of open intervals)

Example · Undergraduate

Terms

Term	This example	Why
topology	✓	The open sets of $\reals$ form a topology because unions and finite intersections of open sets are open.
σ-algebra	✗	The complement of $(0, 1)$ is not open.

Distinctions using this example

• Topology vs. σ-algebra

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