Additivity of the curve degree

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OAI.MaximalSeshadri.Geometry.curveDegree_tensor

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

maximal-seshadrioai-math

For a surface $S$ with an ample bundle, line bundles $L,M$ and an integral curve $C$ : $\deg_C(L\otimes M)=\deg_CL+\deg_CM$ .

Notation. $\deg_CL$ is curveDegree, namely $\chi(L|_C)-\chi(\mathcal O_C)$ . IsAmple means that for each point $x$ and open $V\ni x$ , some positive power has a global section with nonvanishing open containing $x$ , inside $V$ , and affine. A Surface is an integral scheme smooth of relative dimension 2 over $\operatorname{Spec}\mathbb C$ with a closed immersion into some complex projective space over $\mathbb C$ . An IntegralCurve on a surface is an integral closed subscheme of topological Krull dimension one, given by a closed immersion.

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 TopologicalSpace
open MaximalSeshadri.Frames

Formal statement

theorem curveDegree_tensor (S : Surface) (A : LineBundle S.scheme) (hA : A.IsAmple)
    (L M : LineBundle S.scheme) (C : IntegralCurve S) :
    curveDegree S (L.tensor M) C = curveDegree S L C + curveDegree S M C := 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.curveDegree_tensor`, https://github.com/openai/math/blob/adc7f1241b42e322a6451854ab7e4b4c146bf78a/lean/OAI/AlgebraicGeometry/Seshadri/Intersection/AmbientCurveDegree.lean#L18

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