Arnold's corank problem: is the Hessian corank of a hypersurface singularity an ambient topological invariant?
The weighted homogeneous germs on (, divisible by eight) of the Zariski counterexample are ambiently homeomorphic, have isolated critical points and real coefficients, and have Hessian ranks and , 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…