geometry-topology / Singularity theory; topological invariants of hypersurface germs

Arnold's corank problem: is the Hessian corank of a hypersurface singularity an ambient topological invariant?

The weighted homogeneous germs f1,f2f_1,f_2 on CN\mathbb{C}^N (N>3N>3, divisible by eight) of the Zariski counterexample are ambiently homeomorphic, have isolated critical points and real coefficients, and have Hessian ranks 16E>016E>0 and 00, so their coranks differ. Corank parity is preserved, as Sampaio's theorem requires. Nothing is said about corank in three variables (where it is invariant) or about a minimal dimension.

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geometry-topologySep 24, 2026Significance 20/100Registry: unreviewed

Arnold's corank problem: is the Hessian corank of a hypersurface singularity an ambient topological invariant?

Prior state unknown→disproved

The weighted homogeneous germs f1,f2f_1,f_2 on CN\mathbb{C}^N (N>3N>3, divisible by eight) of the Zariski counterexample are ambiently homeomorphic, have isolated critical points and real coefficients, and have Hessian ranks 16E>016E>0 and 00, so their coranks differ. Corank parity is preserved, as Sampaio's theorem requires. Nothing is said about corank in three variables (where it is invariant) or about a minimal dimens…

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The weighted homogeneous germs f1,f2f_1,f_2 on CN\mathbb{C}^N (N>3N>3, divisible by eight) of the Zariski counterexample are ambiently homeomorphic, have isolated critical points and real coefficients, and have Hessian ranks 16E>016E>0 and 00, so their coranks differ. Corank parity is preserved, as Sampaio's theorem requires. Nothing is said about corank in three variables (where it is invariant) or about a minimal dimension.

The weighted homogeneous germs f1,f2f_1,f_2 on CN\mathbb{C}^N (N>3N>3, divisible by eight) of the Zariski counterexample are ambiently homeomorphic, have isolated critical points and real coefficients, and have Hessian ranks 16E>016E>0 and 00, so their coranks differ. Corank parity is preserved, as Sampaio's theorem requires. Nothing is said about corank in three variables (where it is invariant) or about a minimal dimension.

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Arnold's corank problem: is the Hessian corank of a hypersurface singularity an ambient topological invariant? — Mathematical Frontier Network