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==Relations to Lebesgue integral==


It is possible to treat absolutely convergent series as a special case of Lebesgue integrals. To this end, the countable set $\{0,1,2,\dots\}$ is treated as a [[measure space]]; all subsets are measurable, and the ''counting measure'' $\mu$ is used: $\mu(A)$ is the number of points in $A$ ($\infty$ if $A$ is infinite). A sequence $(a_n)_n$ is a function $a:\{0,1,2,\dots\}\to\R$