# Category:Sigma-Rings

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This category contains results about **Sigma-Rings**.

Definitions specific to this category can be found in Definitions/Sigma-Rings.

A **$\sigma$-ring** is a ring of sets which is closed under countable unions.

That is, a ring of sets $\Sigma$ is a **$\sigma$-ring** if and only if:

- $\ds A_1, A_2, \ldots \in \Sigma \implies \bigcup_{n \mathop = 1}^\infty A_n \in \Sigma$

## Pages in category "Sigma-Rings"

The following 3 pages are in this category, out of 3 total.