Nefness criterion for divisors on the iterated blow-up Xn+2,(n−2)\mathcal{X}_{n+2,(n-2)}

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Let SS be the indexing set used to describe the divisor, and let DD be a divisor on Xn+2,(n−2)\mathcal{X}_{n+2,(n-2)} of the form specified in the source’s general divisor expression. Call DD F-nef when all its intersections with the relevant F-curves are nonnegative, equivalently when

AG,J,L≥0A_{G,J,L}\geq 0

and

BI,G,J,L≥0B_{I,G,J,L}\geq 0

for every partition G⊔J⊔L=SG\sqcup J\sqcup L=S and every partition I⊔G⊔J⊔L=SI\sqcup G\sqcup J\sqcup L=S, respectively.

Nefness criterion. The divisor DD is nef if and only if these F-nef inequalities hold.

This is presented as a conjectural nef-cone description for the indicated blow-up. The source does not provide a resolution status beyond stating the criterion.

References

Primary source

Olivia Dumitrescu and Elisa Postinghel, “Positivity of divisors on blown-up projective spaces, II”, arXiv:1709.05012 (2019).

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