geometry-topology / Singularity theory; topology of hypersurface singularities

Zariski's multiplicity conjecture: does embedded topology determine the multiplicity of a hypersurface singularity?

Two independent counterexample constructions. September 24: for some finite N>3N>3 divisible by eight, reduced weighted homogeneous real polynomials f1,f2f_1,f_2 on CN\mathbb{C}^N with isolated critical points, ord0f1=2\mathrm{ord}_0f_1=2, ord0f2=3\mathrm{ord}_0f_2=3, and (CN,V(f1),0)≅(CN,V(f2),0)(\mathbb{C}^N,V(f_1),0)\cong(\mathbb{C}^N,V(f_2),0); the germs are also topologically right equivalent, so the right-equivalence version and its mod-2 version (Sampaio 2025, Conjectures 2 and Z mod 2) fail too. September 27: reduced convergent germs f4,f5f_4,f_5 on C4\mathbb{C}^4 with isolated critical points, orders 44 and 55, ambiently homeomorphic zero sets. Not addressed: hypersurfaces in C3\mathbb{C}^3, and metric (bi-Lipschitz) or family versions, where positive results stand.

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geometry-topologySep 24, 2026Significance 52/100Registry: unreviewed

Zariski's multiplicity conjecture: does embedded topology determine the multiplicity of a hypersurface singularity?

Prior state unknown→disproved

Two independent counterexample constructions. September 24: for some finite N>3N>3 divisible by eight, reduced weighted homogeneous real polynomials f1,f2f_1,f_2 on CN\mathbb{C}^N with isolated critical points, ord0f1=2\mathrm{ord}_0f_1=2, ord0f2=3\mathrm{ord}_0f_2=3, and (CN,V(f1),0)≅(CN,V(f2),0)(\mathbb{C}^N,V(f_1),0)\cong(\mathbb{C}^N,V(f_2),0); the germs are also topologically right equivalent, so the right-equivalence version and its mod-2 version (…

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Two independent counterexample constructions. September 24: for some finite N>3N>3 divisible by eight, reduced weighted homogeneous real polynomials f1,f2f_1,f_2 on CN\mathbb{C}^N with isolated critical points, ord0f1=2\mathrm{ord}_0f_1=2, ord0f2=3\mathrm{ord}_0f_2=3, and (CN,V(f1),0)≅(CN,V(f2),0)(\mathbb{C}^N,V(f_1),0)\cong(\mathbb{C}^N,V(f_2),0); the germs are also topologically right equivalent, so the right-equivalence version and its mod-2 version (Sampaio 2025, Conjectures 2 and Z mod 2) fail too. September 27: reduced convergent germs f4,f5f_4,f_5 on C4\mathbb{C}^4 with isolated critical points, orders 44 and 55, ambiently homeomorphic zero sets. Not addressed: hypersurfaces in C3\mathbb{C}^3, and metric (bi-Lipschitz) or family versions, where positive results stand.

Two independent counterexample constructions. September 24: for some finite N>3N>3 divisible by eight, reduced weighted homogeneous real polynomials f1,f2f_1,f_2 on CN\mathbb{C}^N with isolated critical points, ord0f1=2\mathrm{ord}_0f_1=2, ord0f2=3\mathrm{ord}_0f_2=3, and (CN,V(f1),0)≅(CN,V(f2),0)(\mathbb{C}^N,V(f_1),0)\cong(\mathbb{C}^N,V(f_2),0); the germs are also topologically right equivalent, so the right-equivalence version and its mod-2 version (Sampaio 2025, Conjectures 2 and Z mod 2) fail too. September 27: reduced convergent germs f4,f5f_4,f_5 on C4\mathbb{C}^4 with isolated critical points, orders 44 and 55, ambiently homeomorphic zero sets. Not addressed: hypersurfaces in C3\mathbb{C}^3, and metric (bi-Lipschitz) or family versions, where positive results stand.

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