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An atlas pulled back by a homeomorphism

Definition
SP4PullbackCharts

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

For topological spaces M and N and a chart model H, a homeomorphism e : N ≃ₜ M transports the given H-charted-space structure on M to N by composition of its charts with e. The construction is universe-polymorphic.

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

set_option autoImplicit false

namespace SP4Mission

open _root_.Homeomorph

open Set ChartedSpace

open scoped Manifold Topology

variable {H : Type*} [TopologicalSpace H] {M : Type*} [TopologicalSpace M]
  [ChartedSpace H M] {N : Type*} [TopologicalSpace N]

namespace Homeomorph

@[instance_reducible]
def _root_.Homeomorph.sp4MissionPullbackChartedSpace (e : N ≃ₜ M) : ChartedSpace H N where
  atlas := (e.transOpenPartialHomeomorph ·) '' atlas H M
  chartAt x := e.transOpenPartialHomeomorph (chartAt H (e x))
  mem_chart_source x := mem_chart_source H (e x)
  chart_mem_atlas x := ⟨_, chart_mem_atlas _ (e x), rfl⟩

end Homeomorph

end SP4Mission
Source
Unpublished local Lean source SPC4.lean, SHA-256 b17fdb932034e5211d0db8171c08e2b3a182016bceaecdd2deb49c39d6bfd5cc; supported copy and exact oracle provenance in the accompanying local package. Transported-chart construction and pullback compatibility also use the unpublished local PullbackGroupoid.lean source, SHA-256 f92aabb88c15cd62fd95afdeaa4c155b0daa62a8283b58a0848b576116fc8fa8.
Read-back

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

For every topological model space HHH, every topological space MMM with a specified charted-space structure modeled on HHH, every topological space NNN, and every homeomorphism e:N→Me:N\to Me:N→M, the construction defines a charted-space structure on NNN modeled on the same HHH. Its atlas consists exactly of the charts obtained by first applying eee and then an atlas chart ccc of MMM: such a chart has source e−1(source⁡(c))e^{-1}(\operatorname{source}(c))e−1(source(c)), target target⁡(c)\operatorname{target}(c)target(c), forward map c∘ec\circ ec∘e, and inverse map e−1∘c−1e^{-1}\circ c^{-1}e−1∘c−1. The preferred chart at each x∈Nx\in Nx∈N is obtained from the preferred chart of MMM at e(x)e(x)e(x) by this same composition. The topology on NNN is its given topology, and no earlier chart structure on NNN, differentiability, manifold compatibility, dimension, separation, or nonemptiness hypothesis is required; empty spaces are included whenever the stated homeomorphism exists.

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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