The given equation is $\left(x^{4}+y^{4}\right)^{2}=2013\left(x^{2}-y^{2}\right)$. Differentiating both sides with respect to $x$, we get
\[2\left(x^{4}+y^{4}\right)\left(4x^{3}+4y^{3}\frac{dy}{dx}\right)=2013\left(2x-2y\frac{dy}{dx}\right).\]
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