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An affine cover by twisted sections

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OAI.MaximalSeshadri.Geometry.LineBundle.twist_affine_cover

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

maximal-seshadrioai-math

Let XXX be integral and compact, P,JP,JP,J line bundles, ttt sections of PPP with iso-opens covering XXX, and assume JJJ has affine covers by sections over each iso-open of tit_iti​. Then there are n>0n>0n>0 and a finite family of sections of Pn⊗JP^n\otimes JPn⊗J whose iso-opens cover XXX, are affine and are nonempty.

Notation. The iso-open of sss (SectionOpens.isoOpen s) is the union of the opens on which the morphism sss restricts to an isomorphism.

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 CategoryTheory CategoryTheory.Limits AlgebraicGeometry TopologicalSpace
open MaximalSeshadri.Frames MaximalSeshadri.SectionOpens MaximalSeshadri.Projective

variable {X : Scheme.{0}}

Formal statement
theorem LineBundle.twist_affine_cover [IsIntegral X] [CompactSpace X]
    (P J : LineBundle X) {κ : Type} (t : κ → (O X ⟶ P.sheaf))
    (ht : (⨆ i,isoOpen (t i)) = ⊤)
    (hlocal : ∀ i, ∃ (α : Type)
      (w : α → (O (isoOpen (t i)).toScheme ⟶ J.sheaf.restrict (isoOpen (t i)).ι)),
        (⨆ a,isoOpen (w a)) = ⊤ ∧ ∀ a, IsAffineOpen (isoOpen (w a))) :
    ∃ n : ℕ, 0 < n ∧ ∃ (σ : Type) (_ : Fintype σ)
      (s : σ → (O X ⟶ ((P.pow n).tensor J).sheaf)),
        (⨆ a,isoOpen (s a)) = ⊤ ∧
        (∀ a, IsAffineOpen (isoOpen (s a))) ∧
        (∀ a, (isoOpen (s a) : Set X).Nonempty) := 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.LineBundle.twist_affine_cover`, https://github.com/openai/math/blob/adc7f1241b42e322a6451854ab7e4b4c146bf78a/lean/OAI/AlgebraicGeometry/Seshadri/Geometry/RelativeProjectivity.lean#L22

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