Sottile's general secant conjecture

Let νn\nu\vdash n and let μκ\boldsymbol{\mu}\Vdash\kappa, where κ=(κ1,,κs)\kappa=(\kappa_1,\dots,\kappa_s) is a composition of nn. Let I1,,IsRI_1,\dots,I_s\subseteq\mathbb{R} be pairwise disjoint real intervals. A generalized secant flag to the moment curve γ\gamma along an interval is a complete flag whose subspaces are generalized secants to γ\gamma along that interval. Sottile's general secant conjecture. If F(1),,F(s)F^{(1)}_\bullet,\dots,F^{(s)}_\bullet are generalized secant flags along I1,,IsI_1,\dots,I_s, respectively, then the corresponding Schubert intersection is real and scheme-theoretically reduced. The divisor case is proved in the paper, but the general form remains open.

Sources & referencesView supporting material

Primary source

Steven N. Karp and Kevin Purbhoo, “Universal Plücker coordinates for the Wronski map and positivity in real Schubert calculus”, arXiv:2309.04645 (2026).

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