# Category:Definitions/Measures

This category contains definitions related to Measures.
Related results can be found in Category:Measures.

### Definition 1

$\mu$ is called a measure on $\Sigma$ if and only if $\mu$ fulfils the following axioms:

 $(1)$ $:$ $\ds \forall E \in \Sigma:$ $\ds \map \mu E$ $\ds \ge$ $\ds 0$ $(2)$ $:$ $\ds \forall \sequence {S_n}_{n \mathop \in \N} \subseteq \Sigma: \forall i, j \in \N: S_i \cap S_j = \O:$ $\ds \map \mu {\bigcup_{n \mathop = 1}^\infty S_n}$ $\ds =$ $\ds \sum_{n \mathop = 1}^\infty \map \mu {S_n}$ that is, $\mu$ is a countably additive function $(3)$ $:$ $\ds \exists E \in \Sigma:$ $\ds \map \mu E$ $\ds \in$ $\ds \R$ that is, there exists at least one $E \in \Sigma$ such that $\map \mu E$ is finite

### Definition 2

$\mu$ is called a measure on $\Sigma$ if and only if $\mu$ fulfils the following axioms:

 $(1')$ $:$ $\ds \forall E \in \Sigma:$ $\ds \map \mu E$ $\ds \ge$ $\ds 0$ $(2')$ $:$ $\ds \forall \sequence {S_n}_{n \mathop \in \N} \subseteq \Sigma: \forall i, j \in \N: S_i \cap S_j = \O:$ $\ds \map \mu {\bigcup_{n \mathop = 1}^\infty S_n}$ $\ds =$ $\ds \sum_{n \mathop = 1}^\infty \map \mu {S_n}$ that is, $\mu$ is a countably additive function $(3')$ $:$ $\ds \map \mu \O$ $\ds =$ $\ds 0$

## Subcategories

This category has the following 4 subcategories, out of 4 total.

## Pages in category "Definitions/Measures"

The following 20 pages are in this category, out of 20 total.