Characterization of generically reduced elementary components for two-step nestings

Fix an integer n4n\geqslant 4 and consider a nesting

h=((1,s),(1,k,2)).\underline{\boldsymbol{h}}=((1,s),(1,k,2)).

Let Vh=Hhn×AnV_{\underline{\boldsymbol{h}}}=\overline{H^n_{\underline{\boldsymbol{h}}}}\times \mathbb{A}^n, where HhnH^n_{\underline{\boldsymbol{h}}} is the corresponding nested Hilbert-function stratum. Also write h(2)\boldsymbol{h}^{(2)} for the second Hilbert function in the nesting.

The nesting conjecture. The variety VhV_{\underline{\boldsymbol{h}}} is a generically reduced elementary component if and only if

4kn,2sk2.4\leqslant k\leqslant n,\qquad 2\leqslant s\leqslant k-2.

On the other hand, if h(2)(2)=1\boldsymbol{h}^{(2)}(2)=1, then VhV_{\underline{\boldsymbol{h}}} is contained in the smoothable component.

The claim records the expected component structure for these nested Hilbert schemes. The supplied text gives no resolution status or evidence beyond the claim itself, so it is treated as open.

Sources & referencesView supporting material

Primary source

Michele Graffeo and Paolo Lella, “Components of the nested Hilbert scheme of few points”, arXiv:2601.16765 (2026).

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