# Category:Definitions/Sigma-Rings

This category contains definitions related to Sigma-Rings.
Related results can be found in Category: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:

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

## Subcategories

This category has only the following subcategory.

## Pages in category "Definitions/Sigma-Rings"

The following 5 pages are in this category, out of 5 total.