\begin{definition}[Definition:Lebesgue Sigma-Algebra]
Let $\tau$ be the Euclidean topology on $\R^n$.
Let $\NN$ be the collection of null sets in $\R^n$.
The '''Lebesgue sigma-algebra''' on $\R^n$ is the sigma-algebra generated by the set $\tau \cup \NN$.
{{namedfor|Henri Léon Lebesgue}}
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\end{definition}