Topological four-dimensional Poincaré theorem
OpenSP4Mission.freedman_poincare_topEvery compact Hausdorff Type-0 space charted on real four-space that is homotopy equivalent to the standard four-sphere is homeomorphic to it. A smooth-manifold hypothesis is not required by this exact statement. This is known in the literature, but its Lean proof remains open in this package.
import Definitions.Def_SP4Sphere set_option autoImplicit false open scoped Manifold ContDiff open SP4Mission
theorem SP4Mission.freedman_poincare_top
(M : Type) [TopologicalSpace M] [T2Space M] [CompactSpace M]
[ChartedSpace (EuclideanSpace ℝ (Fin 4)) M] :
Nonempty (ContinuousMap.HomotopyEquiv M S4) → Nonempty (M ≃ₜ S4) := by sorry
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What the Lean code literally says, in plain math · Codex; the exact underlying model identifier is not exposed in this session.
Let with the Euclidean subspace topology. For every type in the base universe equipped with a topology making it compact and Hausdorff and with a specified charted-space structure modeled on , existence of a continuous homotopy equivalence between and —that is, a pair of continuous maps in opposite directions whose two composites are continuously homotopic to the corresponding identity maps—implies existence of a homeomorphism . There is no differentiability or smooth-compatibility assumption on the chart structure and no smoothness conclusion. The homeomorphism is required only to exist, without uniqueness or a prescribed homotopy class. Empty is allowed by the quantified space assumptions, but its homotopy-equivalence premise cannot hold.
Confirmed by the mission captain (proposal self-audit).