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$$\int_{-R}^{R} \frac{1}{\sqrt[d\lambda]{x/\lambda}+\sqrt[d\lambda]{y/f(\lambda)}} = R(x,y)$$

$$\int_{-R}^{R} \frac{1}{\sqrt[d\lambda]{x/\lambda}+\sqrt[d\lambda]{f(x)/f(\lambda)}} = R(x,f(x))$$