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42 changes: 42 additions & 0 deletions LeanEval/Topology/Poincare3DSmooth.lean
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import Mathlib
import EvalTools.Markers

namespace LeanEval
namespace Topology

/-!
# 3D smooth Poincaré conjecture (Perelman)

A `proof_wanted` in `Mathlib/Geometry/Manifold/PoincareConjecture.lean`. Every
simply connected compact Hausdorff 3-manifold that admits a smooth structure
is **diffeomorphic** to the standard 3-sphere `𝕊³`.

This is the smooth-category strengthening of the topological 3D Poincaré
conjecture, also proved by Perelman in 2002–2003. In dimension 3 the smooth
and topological Poincaré conjectures are equivalent (every topological
3-manifold admits a unique smooth structure, by Moise's theorem), but the
formal Lean statement carries the smooth structure explicitly via
`IsManifold (𝓡 3) ∞ M` and concludes with a diffeomorphism in the manifold
type `M ≃ₘ⟮𝓡 3, 𝓡 3⟯ 𝕊³`.

mathlib has `ChartedSpace`, `IsManifold`, `Diffeomorph`, `SimplyConnectedSpace`,
`CompactSpace`, and the unit sphere as a smooth manifold but no Ricci flow,
no Hamilton–Perelman surgery, and no Moise theorem.
-/

open scoped Manifold ContDiff
open Metric (sphere)

/-- **3D smooth Poincaré conjecture** (Perelman, 2002–2003). Every simply
connected compact Hausdorff smooth 3-manifold is diffeomorphic to the
standard 3-sphere `𝕊³`. -/
@[eval_problem]
theorem poincare_3d_smooth
{M : Type*} [TopologicalSpace M] [T2Space M]
[ChartedSpace (EuclideanSpace ℝ (Fin 3)) M] [IsManifold (𝓡 3) ∞ M]
[SimplyConnectedSpace M] [CompactSpace M] :
Nonempty (M ≃ₘ⟮𝓡 3, 𝓡 3⟯ sphere (0 : EuclideanSpace ℝ (Fin 4)) 1) := by
sorry

end Topology
end LeanEval
9 changes: 9 additions & 0 deletions manifests/problems/poincare_3d_smooth.toml
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id = "poincare_3d_smooth"
title = "3D smooth Poincaré conjecture (Perelman)"
test = false
module = "LeanEval.Topology.Poincare3DSmooth"
holes = ["poincare_3d_smooth"]
submitter = "Kim Morrison"
notes = "Every simply connected compact Hausdorff smooth 3-manifold is diffeomorphic to 𝕊³. Recorded as `proof_wanted SimplyConnectedSpace.nonempty_diffeomorph_sphere_three` in `Mathlib/Geometry/Manifold/PoincareConjecture.lean`. The smooth-category strengthening of the topological 3D Poincaré conjecture; also Perelman 2002-2003. In dim 3 the smooth and topological versions are equivalent (Moise's theorem says every topological 3-manifold admits a unique smooth structure), but the Lean statement carries the smooth structure explicitly. Mathlib has all the differential-topology / manifold scaffolding but neither Ricci flow nor Moise's theorem."
source = "G. Perelman, three arXiv preprints 2002-2003 (math/0211159, math/0303109, math/0307245). Recorded as a `proof_wanted` in Mathlib/Geometry/Manifold/PoincareConjecture.lean. In dim 3, Smooth ⇔ PL ⇔ Topological via Moise (1952) / Bing (1959)."
informal_solution = "Apply the topological 3D Poincaré conjecture to obtain a homeomorphism M ≃ₜ S³, then promote it to a diffeomorphism via Moise's theorem (every topological 3-manifold admits a unique smooth structure up to diffeomorphism), or equivalently observe that Hamilton-Perelman Ricci flow with surgery runs in the smooth category and produces a smooth diffeomorphism directly. Either route involves the same Perelman input on the geometric side; the dim-3 special feature is Moise/Bing which collapses the smooth/topological distinction (false in dim 4 and above)."
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