For some distribution $D\in \Delta(\mathcal{X}\times \mathcal{Y} )$ and function $f : \mathcal{X}\times \mathcal{Y} \to \mathbb{R}$, is it true that:\begin{align*}\mathbb{E}_{(x,y)\sim D} [f(x,y)] = \mathbb{E}_{x} [\mathbb{E}_y[f(x,y)\, |\, x]].\end{align*}
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