Fatabbi–Lorenzini's generalized Segre bound for fat points

Let ZZ be a collection of fat points in Pn{\mathbb P}^n. For a linear rr-subspace LPnL\subseteq {\mathbb P}^n, let wL(Z)\operatorname{w}_L(Z) be the sum of the multiplicities of the points of ZZ lying in LL, and let reg(Z)\operatorname{reg}(Z) denote its regularity index. For r=1,,nr=1,\dots,n and for any linear rr-subspace LL of Pn{\mathbb P}^n, set

T(Z,L):=wL(Z)+r2r.T(Z,L):=\left\lfloor\frac{\operatorname{w}_L(Z)+r-2}{r}\right\rfloor.

Fatabbi–Lorenzini's generalized Segre bound. One has

reg(Z)max{T(Z,L):LPn}.\operatorname{reg}(Z)\le\max\{T(Z,L): L\subseteq {\mathbb P}^n\}.

This conjecture seeks an upper bound for the regularity index of arbitrary fat points, extending Segre's bound beyond points in linearly general position. The supplied text gives no resolution evidence, so its status remains open.

Sources & referencesView supporting material

Primary source

Edoardo Ballico, Olivia Dumitrescu and Elisa Postinghel, “On Segre's bound for fat points in P^n”, arXiv:1504.05151 (2015).

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