analysis / Higher-order Fourier analysis

Ben Green's Open Problem 57

For a finite abelian group $G$, let $\Phi(G)$ be the absolutely convex hull of the specified trilinear kernels and $\Phi'(G)$ its restriction where the third factor depends only on $x_1 + x_2$. Is $\Phi(G) = \Phi'(G)$? A counterexample over $\mathbb{Z}/3\mathbb{Z}$ separates the hulls.

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analysisMay 21, 2026Significance 15/100Registry: lean verified

Ben Green's Open Problem 57

Prior state unknowndisproved

intended complex form disproved, with a certified strict support-function gap

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For a finite abelian group $G$, let $\Phi(G)$ be the absolutely convex hull of the specified trilinear kernels and $\Phi'(G)$ its restriction where the third factor depends only on $x_1 + x_2$. Is $\Phi(G) = \Phi'(G)$? A counterexample over $\mathbb{Z}/3\mathbb{Z}$ separates the hulls.

intended complex form disproved, with a certified strict support-function gap

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Ben Green's Open Problem 57 — Mathematical Frontier Network