Series of nonnegative measurable functions can be integrated term by term

For nonnegative measurable series, summation and integration commute, even with value $+\infty$.Suggest a slogan

Let $(X,\mcm,\mu)$ be a measure space and let $f_n\in$ $L^+$ for $n\geq1$. Then \[ \int_X \sum_{n=1}^\infty f_n\dmu = \sum_{n=1}^\infty\int_X f_n\dmu \] in $[0,\infty]$ [@Fol13].