... case¹

where one distinguishes 4k²(1-k²) or (1-k²)/2k for N respectively odd or even.

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... counterpart²

We note that $J_3(x)=f\left(2(1-x^3)^{1/3}\right)$ where f is the Belyi function of the tetrahedron, see [33], p. 376.

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