# Carathéodory's Theorem (Measure Theory)/Corollary

## Corollary to Carathéodory's Theorem (Measure Theory)

Let $X$ be a set.

Let $\SS \subseteq \powerset X$ be a semi-ring of subsets of $X$.

Let $\mu: \SS \to \overline \R$ be a pre-measure on $\SS$.

Let $\map \sigma \SS$ be the $\sigma$-algebra generated by $\SS$.

Suppose there exists an exhausting sequence $\sequence {S_n}_{n \mathop \in \N} \uparrow X$ in $\SS$ such that:

$\forall n \in \N: \map \mu {S_n} < +\infty$

Then the extension $\mu^*$ is unique.

## Source of Name

This entry was named for Constantin Carathéodory.