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Is this double integral of Fourier series always real?

Consider $f(x)$ a function from $\mathbb{R^+}$ to $\mathbb{C}$ such that $f(x) \sim_0 x$ and $\int_{0}^{\infty} f(x) dx=\int_{0}^{\infty} x^2 f(x) dx=0$ Can we demonstrate that following integral is ...
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Fubini: can we interchange integration order on this double integral (with Fourier series product)

Can we interchange the order of integration of following double integral ? $$I = \int_{0}^{1} \int_{0}^{\infty} F(x,y) \overline{R(x,y)} - R(x,y) \overline{F(x,y)} \; dx \; dy$$ Where $F(x,y)= \...
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