i need help with this theoretical exercise with Riemann integration, hope you can help me. Thanks.
Prove that if $f:\mathbb{R}\rightarrow\mathbb{R}$ is continuous $\vert f\vert$ Riemann integrable on $\mathbb{R}$ and $$\int_{-\infty}^{+\infty}\int_{-\infty}^{+\infty} \frac{\vert f(x)-f(y) \vert}{\vert x-y\vert ^2} dxdy < +\infty$$ $f$ turns out to be constant.