===== σ-algebra =====
==== Set ====
| @#55CCEE: context     | @#55CCEE: $X$ |
| @#FFBB00: definiendum | @#FFBB00: $\Sigma$ in it |
| @#55EE55: postulate   | @#55EE55: $\Sigma\subseteq \mathcal P(X)$ |
| @#55EE55: postulate   | @#55EE55: $ \Sigma\ne\emptyset $ |
| forall                | $E\in\Sigma$ |
| @#55EE55: postulate   | @#55EE55: $ X\smallsetminus E \in \Sigma $ |
| forall                | $A\in\mathrm{Sequence}(\Sigma)$ |
| forall                | $n\in \mathbb N$ |
| @#55EE55: postulate   | @#55EE55: $ \bigcup_{i=1}^n A_i \in \Sigma $ |

==== Ramifications ====
==== Reference ====
Wikipedia: [[http://en.wikipedia.org/wiki/Sigma-algebra|Sigma-algebra]]
==== Parents ====
=== Subset of ===
[[Power set]]
=== Equivalent to ===
[[Measurable space]]
=== Related ===
[[Countable union]]