σ-algebra

Set

context $X$
definiendum $\Sigma$ in it
postulate $\Sigma\subseteq \mathcal P(X)$
postulate $ \Sigma\ne\emptyset $
forall $E\in\Sigma$
postulate $ X\smallsetminus E \in \Sigma $
forall $A\in\mathrm{Sequence}(\Sigma)$
forall $n\in \mathbb N$
postulate $ \bigcup_{i=1}^n A_i \in \Sigma $

Ramifications

Reference

Wikipedia: Sigma-algebra

Parents

Subset of

Power set

Equivalent to

Measurable space

Countable union