Source: wikibot/sigma-ideal
= Sigma-ideal
{wiki=Sigma-ideal}
In the context of set theory and measure theory, a **σ-ideal** (sigma-ideal) is a specific type of collection of sets that satisfies certain properties concerning the operations of countable unions and subsets. More formally, a family \\( I \\) of subsets of a set \\( X \\) is called a σ-ideal if it satisfies the following conditions: 1. **Non-empty:** The empty set is an element of \\( I \\), i.e.