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Sections on the blow-up are bounded by curve bounds

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OAI.MaximalSeshadri.Geometry.PointBlowup.section_curve_bound

by wurtle · Nov 4, 2026 · Mathlib 0df444a (Lean v4.33.1)

maximal-seshadrioai-math

Let SSS be a surface with ample LLL, ppp a configuration of rrr points, BBB a point blow-up of SSS at ppp with projection fff, and J,ιJ,\iotaJ,ι presenting the pullback of the centre ideal. Let w≥0w\ge0w≥0 with w⋅mult⁡p(C)≤deg⁡CLw\cdot\operatorname{mult}_p(C)\le\deg_C Lw⋅multp​(C)≤degC​L for all integral curves CCC on SSS. If k,m∈Nk,m\in\mathbb Nk,m∈N and qqq is a nonzero section of Jm⊗f∗LkJ^{m}\otimes f^*L^{k}Jm⊗f∗Lk on BBB, then w rm≤k L2w\,rm\le k\,L^2wrm≤kL2.

Notation. L2L^2L2 is selfIntersection, namely χ(L2)−2χ(L)+χ(OS)\chi(L^2)-2\chi(L)+\chi(\mathcal O_S)χ(L2)−2χ(L)+χ(OS​). deg⁡CL\deg_CLdegC​L is curveDegree, namely χ(L∣C)−χ(OC)\chi(L|_C)-\chi(\mathcal O_C)χ(L∣C​)−χ(OC​). mult⁡p(C)\operatorname{mult}_p(C)multp​(C) is totalMultiplicity, the sum over the points of curveMultiplicity, the order of the kernel ideal of the local ring map of CCC at the point. PresentsPullbackIdeal I f J ι says that ι:J→OY\iota:J\to\mathcal O_Yι:J→OY​ is a monomorphism whose image on affine opens is the extension of III along fff. IsAmple means that for each point xxx and open V∋xV\ni xV∋x, some positive power has a global section with nonvanishing open containing xxx, inside VVV, and affine. A Surface is an integral scheme smooth of relative dimension 2 over Spec⁡C\operatorname{Spec}\mathbb CSpecC with a closed immersion into some complex projective space over C\mathbb CC. An IntegralCurve on a surface is an integral closed subscheme of topological Krull dimension one, given by a closed immersion. Configuration S r is the set of rrr-tuples of complex points with distinct images, with the Zariski topology induced from the product.

Formalization Note The statement is verbatim from OpenAI's Lean development, with Definitions files of this development imported in place of the upstream modules; these are supporting code for the statement.

Preamble
import Mathlib
import Definitions.Def_MaximalSeshadriConstants
import Definitions.Def_SeshadriPrelim6

namespace OAI

section

namespace MaximalSeshadri.Geometry
noncomputable section
open AlgebraicGeometry CategoryTheory CategoryTheory.Limits TopologicalSpace
open MaximalSeshadri.Frames MaximalSeshadri.ProjectiveBertini

Formal statement
theorem PointBlowup.section_curve_bound (S : Surface) (L : LineBundle S.scheme)
    (hL : L.IsAmple) {r : ℕ} {p : Configuration S r} (B : PointBlowup S r p)
    (J : LineBundle B.surface.scheme) (ι : J.sheaf ⟶ O B.surface.scheme)
    (hJ : PresentsPullbackIdeal (centreIdeal S r p) B.projection J ι)
    (w : ℝ) (hw : 0 ≤ w)
    (hC : ∀ C : IntegralCurve S,
      w*(totalMultiplicity S r C p:ℝ) ≤ (curveDegree S L C:ℝ))
    (k m : ℕ)
    (q : O B.surface.scheme ⟶ ((J.pow m).tensor ((L.pow k).pullback B.projection)).sheaf)
    (hq : q ≠ 0) : w*((r*m:ℕ):ℝ) ≤ (k:ℝ)*selfIntersection S L := by
  sorry

end
end MaximalSeshadri.Geometry
end
end OAI
Source
OpenAI, Maximal Seshadri constants on arbitrary polarized surfaces, September 23, 2026, https://github.com/openai/math (paper: preprints/Maximal-Seshadri-Constants-on-Arbitrary-Polarized-Surfaces-September-23-2026/main.pdf; Lean: lean/OAI/AlgebraicGeometry/Seshadri, Apache License 2.0); Lean declaration `OAI.MaximalSeshadri.Geometry.PointBlowup.section_curve_bound`, https://github.com/openai/math/blob/adc7f1241b42e322a6451854ab7e4b4c146bf78a/lean/OAI/AlgebraicGeometry/Seshadri/Blowup/BlowupForbiddenSection.lean#L23

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