The secant-flag monotone conjecture

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Let γ\gamma be the rational normal curve, and for a set Si={si1,…,sin}S_i=\{s_{i1},\dotsc,s_{in}\} of nn distinct points of RP1\mathbb{R}\mathbb{P}^1, let F∙(Si)F_\bullet(S_i) be the flag whose rr-dimensional member is spanned by the first rr points of the corresponding set. Say that (S1,…,Sm)(S_1,\dotsc,S_m) is monotone with respect to a Grassmannian Schubert problem (w1,…,wm)(w_1,\dotsc,w_m) if the sets lie in pairwise disjoint intervals whose associated points are monotone with respect to the problem. Secant-flag conjecture. For a Grassmannian Schubert problem on Fℓ(α;n)\mathbb{F}\ell(\alpha;n), the intersection

Xw1F∙(S1)∩Xw2F∙(S2)∩⋯∩XwmF∙(Sm)X_{w_1}F_\bullet(S_1)\cap X_{w_2}F_\bullet(S_2)\cap\dotsb\cap X_{w_m}F_\bullet(S_m)

is transverse and all points of intersection are real whenever (S1,…,Sm)(S_1,\dotsc,S_m) is monotone. Results of Eremenko, Gabrielov, Shapiro, and Vainshtein prove special cases; the general statement remains open.

References

Primary source

James Ruffo, Yuval Sivan, Evgenia Soprunova and Frank Sottile, “Experimentation and conjectures in the real Schubert calculus for flag manifolds”, arXiv:math/0507377 (2005).

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