geometry-topology / Singularity theory; Milnor fibres and contact loci

The Budur-Fernandez de Bobadilla-Le-Nguyen conjecture on initial-form Milnor fibres of topologically equivalent germs

With f1,f2f_1,f_2 the Zariski counterexample germs, f~j=fj(z)+t2\tilde f_j=f_j(z)+t^2 on CN+1\mathbb{C}^{N+1} are topologically right equivalent with isolated critical points, but H0((f~1)∗−1(1);Z)≅ZH_0((\tilde f_1)_*^{-1}(1);\mathbb{Z})\cong\mathbb{Z} while H0((f~2)∗−1(1);Z)≅Z2H_0((\tilde f_2)_*^{-1}(1);\mathbb{Z})\cong\mathbb{Z}^2: one initial-form Milnor fibre is connected and the other has two components. This disproves both the embedded and the right-equivalence formulations. It says nothing about weaker invariants the conjecture was meant to capture, such as cohomology of contact loci.

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geometry-topologySep 24, 2026Significance 15/100Registry: unreviewed

The Budur-Fernandez de Bobadilla-Le-Nguyen conjecture on initial-form Milnor fibres of topologically equivalent germs

Prior state unknown→disproved

With f1,f2f_1,f_2 the Zariski counterexample germs, f~j=fj(z)+t2\tilde f_j=f_j(z)+t^2 on CN+1\mathbb{C}^{N+1} are topologically right equivalent with isolated critical points, but H0((f~1)∗−1(1);Z)≅ZH_0((\tilde f_1)_*^{-1}(1);\mathbb{Z})\cong\mathbb{Z} while H0((f~2)∗−1(1);Z)≅Z2H_0((\tilde f_2)_*^{-1}(1);\mathbb{Z})\cong\mathbb{Z}^2: one initial-form Milnor fibre is connected and the other has two components. This disproves both the embedded and the right-equivalen…

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With f1,f2f_1,f_2 the Zariski counterexample germs, f~j=fj(z)+t2\tilde f_j=f_j(z)+t^2 on CN+1\mathbb{C}^{N+1} are topologically right equivalent with isolated critical points, but H0((f~1)∗−1(1);Z)≅ZH_0((\tilde f_1)_*^{-1}(1);\mathbb{Z})\cong\mathbb{Z} while H0((f~2)∗−1(1);Z)≅Z2H_0((\tilde f_2)_*^{-1}(1);\mathbb{Z})\cong\mathbb{Z}^2: one initial-form Milnor fibre is connected and the other has two components. This disproves both the embedded and the right-equivalence formulations. It says nothing about weaker invariants the conjecture was meant to capture, such as cohomology of contact loci.

With f1,f2f_1,f_2 the Zariski counterexample germs, f~j=fj(z)+t2\tilde f_j=f_j(z)+t^2 on CN+1\mathbb{C}^{N+1} are topologically right equivalent with isolated critical points, but H0((f~1)∗−1(1);Z)≅ZH_0((\tilde f_1)_*^{-1}(1);\mathbb{Z})\cong\mathbb{Z} while H0((f~2)∗−1(1);Z)≅Z2H_0((\tilde f_2)_*^{-1}(1);\mathbb{Z})\cong\mathbb{Z}^2: one initial-form Milnor fibre is connected and the other has two components. This disproves both the embedded and the right-equivalence formulations. It says nothing about weaker invariants the conjecture was meant to capture, such as cohomology of contact loci.

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