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Revision difference : $\sigma$-finite
Version 3 Version 2
\paragraph{Definition} \paragraph{Definition}
Let $(\Omega, \mu)$ be a measurable space. Let $\sequence{A_n}$ be a finite or countable sequence such that $\mu(A_k) < \infty$ and $\Omega = \cup_{n} A_n$. $\mu$ is called \emph{$\sigma$-finite} (or \emph{sigma-finite}) iff Let $(\Omega, \mu)$ be a measurable space. Let $\sequence{A_n}$ be a finite or countable sequence such that $\mu(A_k) < \infty$ and $\Omega = \cup_{n} A_n$. $\mu$ is called \emph{$\sigma$-finite} (or \emph{sigma-finite}) iff
\begin{equation*} \begin{equation*}
\mu(\Omega) < \infty. \mu(\Omega) < \infty.
\end{equation*} \end{equation*}
If $\mu$ is not $\sigma$-finite, it is called \emph{$\sigma$-infinite}. If $\mu$ is not $\sigma$-finite, it is called \emph{$\sigma$-infinite}.