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The arbitrary-atlas transported formulation of smooth Poincaré

Definition
SP4PullbackForm

by ryanshin · Sep 5, 2026 · Mathlib 0df444a (Lean v4.33.1)

This defines the predicate asserting that, for every compact Hausdorff Type-0 smooth four-manifold N with an arbitrary given atlas and every homeomorphism e from N to the standard sphere, there exists a smooth-groupoid structomorphism from the given atlas to the atlas pulled back along e. Its underlying self-homeomorphism of N need not be the identity. The definition does not prove the predicate.

Definition code
-- Derived from frozen local sources; exact source/hash provenance in items.json.
import Definitions.Def_SP4Sphere
import Definitions.Def_SP4PullbackCharts

set_option autoImplicit false

namespace SP4Mission

open scoped Manifold ContDiff

noncomputable section

section Transport

variable {N : Type} [TopologicalSpace N]

def SPC4Pullback : Prop :=
  ∀ (N : Type) [TopologicalSpace N] [T2Space N] [CompactSpace N]
    [cs : ChartedSpace (EuclideanSpace ℝ (Fin 4)) N] [IsManifold (𝓡 4) ∞ N],
    ∀ e : N ≃ₜ S4,
      Nonempty (@Structomorph (EuclideanSpace ℝ (Fin 4)) _
        (contDiffGroupoid ∞ (𝓡 4)) N N _ _ cs e.sp4MissionPullbackChartedSpace)

end Transport

section Bridge

open Set ChartedSpace

variable {𝕜 : Type*} [NontriviallyNormedField 𝕜] {E : Type*} [NormedAddCommGroup E]
  [NormedSpace 𝕜 E] {H' : Type*} [TopologicalSpace H'] {I : ModelWithCorners 𝕜 E H'}
  {X : Type*} [TopologicalSpace X] [ChartedSpace H' X]
  {X' : Type*} [TopologicalSpace X'] [ChartedSpace H' X']
  {m : ℕ∞ω} [IsManifold I m X] [IsManifold I m X']

end Bridge

end

end SP4Mission
Source
Unpublished local Lean source SPC4.lean, SHA-256 b17fdb932034e5211d0db8171c08e2b3a182016bceaecdd2deb49c39d6bfd5cc; supported copy and exact oracle provenance in the accompanying local package.
Read-back

What the Lean code literally says, in plain math · Codex; the exact underlying model identifier is not exposed in this session.

Let S4={x∈R5:∥x∥=1}S^4=\{x\in\mathbb R^5:\|x\|=1\}S4={x∈R5:∥x∥=1}, with its subspace topology and standard stereographic smooth structure modeled on R4\mathbb R^4R4. The proposition SPC4Pullback\mathrm{SPC4Pullback}SPC4Pullback states that, for every type NNN in the base universe equipped with a topology making it compact and Hausdorff, every specified charted-space structure AAA on NNN modeled on R4\mathbb R^4R4 with C∞C^\inftyC∞-compatible transitions, and every homeomorphism e:N→S4e:N\to S^4e:N→S4, there exists a homeomorphism h:N→Nh:N\to Nh:N→N preserving the smooth structure from AAA on the source to the structure pulled back from S4S^4S4 along eee on the target. The pulled-back atlas consists exactly of d∘ed\circ ed∘e for sphere atlas charts ddd, with source e−1(source⁡(d))e^{-1}(\operatorname{source}(d))e−1(source(d)), target target⁡(d)\operatorname{target}(d)target(d), inverse e−1∘d−1e^{-1}\circ d^{-1}e−1∘d−1, and preferred chart at xxx induced by the sphere's preferred chart at e(x)e(x)e(x). Structure preservation means that for every chart ccc in AAA and every sphere atlas chart ddd, the open partial homeomorphism represented by (d∘e)∘h∘c−1(d\circ e)\circ h\circ c^{-1}(d∘e)∘h∘c−1 belongs to the groupoid of smooth local transformations of R4\mathbb R^4R4: both it and its inverse are C∞C^\inftyC∞ on their domains. The choice of hhh may depend on eee, and no condition that hhh be the identity or unique is present. The quantifier over eee has no instances if NNN is empty.

Human review
  • Endorsed by Shuze Chen · Sep 6, 2026

  • Endorsed by ryanshin · Sep 6, 2026

    Confirmed by the mission captain (proposal self-audit).

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