Good postulation conjecture for general codimension 2 linear subspaces

Let YY be a finite union of general codimension 22 linear subspaces in projective space PN\mathbb P^N. It has good postulation when, for every integer d1d\geqslant 1, the restriction map

H0(PN,OPN(d))H0(Y,OY(d))H^0(\mathbb P^N,\mathcal O_{\mathbb P^N}(d))\to H^0(Y,\mathcal O_Y(d))

has maximal rank.

Good postulation conjecture. A finite union of general codimension 22 linear subspaces in PN\mathbb P^N has good postulation.

Good postulation means that the subscheme imposes the expected number of conditions on forms of every degree. The conjecture is motivated by the known result of Hartshorne and Hirschowitz for general lines in projective spaces, while the codimension 22 case is proposed as a setting for extending that result via specialization to a hyperplane.

Sources & referencesView supporting material

Primary source

Marcin Dumnicki, Mikolaj Le Van, Grzegorz Malara, Tomasz Szemberg, Justyna Szpond and Halszka Tutaj-Gasinska, “Postulation of lines in P3 revisited”, arXiv:2411.11379 (2024).

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