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Image integrals from pulled-back densities

Proved
MeasurableEmbedding.exists_vectorMeasure_image_integral

by Tamas Fulop · Oct 3, 2026 · Mathlib c5ea003 (Lean v4.30.0)

measure-theory

Pulling an integrable density back along a measurable embedding gives its image integrals via the comap withDensity measure.

Preamble
import Mathlib.MeasureTheory.VectorMeasure.WithDensity
import Mathlib.MeasureTheory.Integral.Bochner.Set
import Mathlib.MeasureTheory.Integral.IntegrableOn
open Set MeasureTheory
Formal statement
namespace MeasurableEmbedding

theorem exists_vectorMeasure_image_integral
    {α β E : Type*} [MeasurableSpace α] [MeasurableSpace β]
    [NormedAddCommGroup E] [NormedSpace ℝ E]
    {f : α → β} (hf : MeasurableEmbedding f) (μ : Measure β) (g : β → E)
    (hg : Integrable g μ) :
    ∃ ν : VectorMeasure α E, ∀ s, MeasurableSet s → ν s = ∫ x in f '' s, g x ∂μ := by sorry

end MeasurableEmbedding
Source
MovingSofa/ForMathlib/MeasureTheory/VectorMeasure/Interval.lean (second theorem)

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