l2_pullback_range_eq_lpMeas

Plain-English statement

Arbitrary measurable spaces/measures; genuine measure-preserving map. Exact range equals comap AE strongly measurable L2 submodule, with internally constructed factor and MemLp transfer; no probability/finite-measure/StandardBorel premise. Actual PBPS consumer. Independently verified 8c8847715c1d4c3033224b069d8dd694f2a4bd30.

Scope guard. This card records a compiled local declaration. Its mathematical scope is exactly the Lean statement below; the Registry note and source correspondence may describe motivation but do not strengthen it.

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Lean statement

theorem l2_pullback_range_eq_lpMeas
    {X Y : Type*} [MeasurableSpace X] [MeasurableSpace Y]
    {μ : Measure X} {ν : Measure Y} {f : X → Y}
    (hf : MeasurePreserving f μ ν) :
    (Lp.compMeasurePreservingₗᵢ ℝ f hf).toLinearMap.range =
      lpMeas ℝ ℝ (MeasurableSpace.comap f (inferInstance : MeasurableSpace Y)) 2 μ := by
  classical
  ext v
  constructor
  · rintro ⟨u, rfl⟩
    apply mem_lpMeas_iff_aestronglyMeasurable.mpr
    have hu : AEStronglyMeasurable (u : Y → ℝ) (μ.map f) := by
      rw [hf.map_eq]
      exact Lp.aestronglyMeasurable u
    exact (hu.comp_ae_measurable' hf.aemeasurable).congr
      (Lp.coeFn_compMeasurePreserving u hf).symm
  · intro hv
    have hm := mem_lpMeas_iff_aestronglyMeasurable.mp hv
    obtain ⟨g, hg, heq⟩ := hm.stronglyMeasurable_mk.exists_eq_measurable_comp
    have hvg : (v : X → ℝ) =ᵐ[μ] g ∘ f :=
      hm.ae_eq_mk.trans (Filter.Eventually.of_forall (fun x => congrFun heq x))
    have hcomp : MemLp (g ∘ f) 2 μ := (Lp.memLp v).ae_eq hvg
    have hgLp : MemLp g 2 ν := by
      rw [← hf.map_eq]
      exact (memLp_map_measure_iff hg.aestronglyMeasurable hf.aemeasurable).mpr hcomp
    have hgAE : (hgLp.toLp g : Y → ℝ) =ᵐ[μ.map f] g := by
      rw [hf.map_eq]
      exact hgLp.coeFn_toLp
    refine ⟨hgLp.toLp g, ?_⟩
    apply Lp.ext
    exact (Lp.coeFn_compMeasurePreserving (hgLp.toLp g) hf).trans
      ((ae_eq_comp hf.aemeasurable hgAE).trans hvg.symm)

end
end AutoSamplingTheory.TechnicalLemmas.Measure.L2PullbackRange

Open AutoSamplingTheory/TechnicalLemmas/Measure/L2PullbackRange.lean:14published source at ed709a7f320d

Proof architecture

Actual PBPS consumer; no SALD admission

Lean proof walkthrough

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Hidden assumptions and non-claims

Measurability is represented explicitly or must be supplied by a dependency.
Almost-everywhere hypotheses depend on the stated measure and representative.