Product of a singular and continuous measures

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Suppose we have a function $f(x,y)\geq 0$ and we integrate it with respect to a measure $\mu=\mu_{\mathrm{a.c.}}+\mu_{\mathrm{disc}}+\mu_{\mathrm{s.c}}$. Is it true that \begin{equation} \iint f(x,y)d\mu(x)d\mu(y)=\iint f(x,y)d\mu_{\mathrm{a.c.}}(x)d\mu_{\mathrm{a.c.}}(y)+ \iint f(x,y)d\mu_{\mathrm{disc}}(x)d\mu_{\mathrm{disc}}(y)\\+\iint f(x,y)d\mu_{\mathrm{s.c}}(x)d\mu_{\mathrm{s.c}}(y), \end{equation} since for all other combinations of measures the integral is 0? Why/why not?