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Jul 22, 2017 at 12:12 comment added Saal Hardali The hessian can be defined in a completely algebraic manner at a singular point ($df=0$). Without loss of generality assume $f=0$ at the critical point. Consider the 2nd order jet sequence $0 \to Sym^2 \mathcal{T}^*_X \to \mathcal{J}^2 \to \mathcal{J}^1 \to 0$. Since the 1-st order jet vanishes at the critical point $f$ defines a unique symmteric bilinear form on the tangent space. Regarding the second part it depends what you mean by "poincare polynomial. There are many cohomology theories for smooth affine schemes.
Sep 6, 2016 at 15:13 comment added Elden Elmanto you mean the index of a critical point of $f$?
Aug 3, 2016 at 3:42 history asked 54321user CC BY-SA 3.0