Positivity of the radicand of the Cartesian outer metric

Proved

OAI.CKSCartesianOuter.cartesian_radicand_positive

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

cks-bondi-penrosegeneral-relativityoai-math

Here $f_0$ is a smooth function on the unit sphere $S^2$ , $m$ a real number, and $R$ the replacement radius. There is $R_0\ge 12$ such that for all $R\ge R_0$ and $x\in\mathbb R^3$ with $\|x\|\ge 3R$ ,

1+v_R(\|x\|)^2-\frac{2\,\texttt{cartMass}(f_0,m,R,x)}{\|x\|}>0.

Writing $Q$ for this quantity (radicand f₀ m R x) and $\nu$ for the unit normal $x/\|x\|$ , this positivity is what makes the outer metric $\delta+(Q^{-1}-1)\,\nu\otimes\nu$ well defined on the region $\|x\|\ge 3R$ .

Formal statement. In the scope of the preamble:

theorem cartesian_radicand_positive (f₀ : C(Sphere,ℝ)) (hf₀ : SmoothSphere f₀) (m : ℝ) :
    ∃ R₀ : ℝ, 12 ≤ R₀ ∧ ∀ R : ℝ, R₀ ≤ R → ∀ x : E, 3*R ≤ ‖x‖ →
      0 < radicand f₀ m R x

Formalization Note The statement is verbatim from lean/OAI/Geometry/Relativity/CKS/TailEnergy.lean, lines 951-961, in OpenAI's openai/math at commit adc7f12 (Apache-2.0), formalizing part of the construction in the preprint Area-controlled end replacement and the Bondi–Penrose inequality in the CKS class (OpenAI, September 27, 2026). It is a supporting lemma for OAI.CKSSourceExterior.area_controlled_end_replacement. The definitions it mentions are those of Definitions.Def_CKSBondiPenrose and Definitions.Def_CKSEndReplacementSupport.

Preamble

import Mathlib
import Definitions.Def_CKSBondiPenrose
import Definitions.Def_CKSEndReplacementSupport

namespace OAI

namespace CKSSpatialManifold

end CKSSpatialManifold

noncomputable section
namespace CKSSphericalChart
noncomputable section
open Set Filter CKSCalculus CKSRound CKSRealizedRound CKSSphericalHarmonics CKSInducedSphere CKSBending CKSLocalBending
open scoped Topology ContDiff

end
end CKSSphericalChart

end

noncomputable section
namespace CKSAngularGeometry
noncomputable section
open Matrix CKSCalculus Filter
open scoped BigOperators Topology ContDiff Matrix.Norms.Elementwise

end
end CKSAngularGeometry

end

noncomputable section
namespace CKSAngularGeometry
noncomputable section
open Matrix CKSCalculus Filter
open scoped BigOperators Topology ContDiff Matrix.Norms.Elementwise

end
end CKSAngularGeometry

end

noncomputable section
namespace CKSAngularGeometry
noncomputable section
open Matrix CKSCalculus Filter
open scoped BigOperators Topology ContDiff Matrix.Norms.Elementwise

end
end CKSAngularGeometry

end

noncomputable section
namespace CKSAmbientCalculus
noncomputable section
open Matrix CKSCalculus CKSAngularGeometry Filter
open scoped BigOperators Topology ContDiff Matrix.Norms.Elementwise

end
end CKSAmbientCalculus

end

noncomputable section
namespace CKSAmbientCalculus
noncomputable section
open Matrix CKSAngularGeometry
open scoped BigOperators

end
end CKSAmbientCalculus

end

noncomputable section
namespace CKSAngularGeometry
noncomputable section
open Matrix CKSCalculus Filter
open scoped BigOperators Topology ContDiff Matrix.Norms.Elementwise

end
end CKSAngularGeometry

end

noncomputable section
namespace CKSAngularGeometry
noncomputable section
open Matrix CKSCalculus Filter
open scoped BigOperators Topology ContDiff Matrix.Norms.Elementwise

end
end CKSAngularGeometry

end

noncomputable section
namespace CKSAngularGeometry
noncomputable section
open Matrix CKSCalculus Filter
open scoped BigOperators Topology ContDiff Matrix.Norms.Elementwise

end
end CKSAngularGeometry

end

noncomputable section
namespace CKSAngularGeometry
noncomputable section
open Matrix CKSCalculus Filter
open scoped BigOperators Topology ContDiff Matrix.Norms.Elementwise

end
end CKSAngularGeometry

end

noncomputable section
namespace CKSAngularGeometry
noncomputable section
open Matrix CKSCalculus Filter
open scoped BigOperators Topology ContDiff Matrix.Norms.Elementwise

end
end CKSAngularGeometry

end

noncomputable section
namespace CKSRealizedRound
noncomputable section
open Matrix CKSCalculus
open scoped Topology ContDiff Matrix.Norms.Elementwise

end
end CKSRealizedRound

end

noncomputable section
namespace CKSSphericalChart
noncomputable section
open Set Filter CKSCalculus CKSAngularGeometry CKSRealizedRound
open scoped Topology ContDiff Matrix.Norms.Elementwise Matrix

end
end CKSSphericalChart

end

noncomputable section
namespace CKSCartesianOuter
noncomputable section
open Set Filter Matrix CKSADM CKSInducedSphere CKSSphericalHarmonics CKSSphericalChart CKSBending
  CKSRealizedRound
open scoped Topology ContDiff Matrix.Norms.Elementwise

end
end CKSCartesianOuter

end

noncomputable section
namespace CKSCartesianOuter
noncomputable section
open Set Filter Matrix CKSADM CKSInducedSphere CKSSphericalHarmonics CKSSphericalChart CKSBending
  CKSRealizedRound
open scoped Topology ContDiff Matrix.Norms.Elementwise

end
end CKSCartesianOuter

end

noncomputable section
namespace CKSCartesianOuter
noncomputable section
open Set Filter Matrix CKSADM CKSInducedSphere CKSSphericalHarmonics CKSSphericalChart CKSBending
  CKSRealizedRound
open scoped Topology ContDiff Matrix.Norms.Elementwise

Formal statement

theorem cartesian_radicand_positive (f₀ : C(Sphere,ℝ)) (hf₀ : SmoothSphere f₀) (m : ℝ) :
    ∃ R₀ : ℝ, 12 ≤ R₀ ∧ ∀ R : ℝ, R₀ ≤ R → ∀ x : E, 3*R ≤ ‖x‖ →
      0 < radicand f₀ m R x := by
  sorry

end
end CKSCartesianOuter
end
end OAI

Source

https://github.com/openai/math/blob/adc7f1241b42e322a6451854ab7e4b4c146bf78a/lean/OAI/Geometry/Relativity/CKS/TailEnergy.lean#L951-L961 ; preprint preprints/Area-controlled-end-replacement-and-the-Bondi-Penrose-inequality-in-the-CKS-class-September-27-2026/paper.pdf in the same repository

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