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Nagata-Biran-Szemberg Conjecture


The qualitative Nagata-Biran-Szemberg conjecture asserts that multipoint Seshadri constants of a fixed polarized variety attain their volume upper bound at sufficiently many very general points. For a smooth integral complex projective variety X of dimension n>=2 with ample line bundle L, it asks for an integer r_0(X,L) such that

 epsilon(X,L;p)=(L^n/r)^(1/n)

at very general distinct tuples for every integer r>=r_0(X,L). The surface form is also called the qualitative Nagata-Biran conjecture. It asks for exact equality at each sufficiently large point count, rather than an asymptotic ratio.

For the projective plane the Nagata conjecture makes the sharper prediction starting at ten points, including a strict degree-multiplicity inequality.

For surfaces, Bruce (2026, Theorem B) reports an explicit threshold. Let X be a smooth connected two-dimensional projective variety over an uncountable algebraically closed field of characteristic zero, and let H be an ample line bundle. Choose an integer k>=1 such that H^( tensor k) is very ample and (X,H^( tensor k))!=(P^2,O_(P^2)(1)). At very general distinct r-tuples, the reported equality is

 epsilon(X,H;p)=sqrt(H^2/r)

for every r>=4k^2H^2, where H^2 is the self-intersection number. The argument is a tropical reworking of earlier AI-generated methods. This surface result does not settle the higher-dimensional assertion.


See also

Nagata Conjecture, Nef Divisor, Seshadri Constant

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References

Bruce, J. "A Tropical Viewpoint on the Nagata-Biran-Szemberg Conjecture." 30 Oct 2026. https://arxiv.org/abs/2610.41931v1.Roé, J. and Ross, J. "An Inequality Between Multipoint Seshadri Constants." Geom. Dedicata 140, 175-181, 2009. https://doi.org/10.1007/s10711-008-9315-4.

Cite this as:

Weisstein, Eric W. "Nagata-Biran-Szemberg Conjecture." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Nagata-Biran-SzembergConjecture.html

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