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L¹ Convergence of Normalized Gaussian Smoothing

Proved
FunctionalInequalities.KLS.LogConcave.GaussianSmoothing.normalizedDensity_tendsto_L1_readable

by Lazyfill · Oct 26, 2026 · Mathlib 0df444a (Lean v4.33.1)

functional-inequalitieskls-conjecturekls-modularkls-readablelog-concave

This statement proves convergence in L1L^1L1 of normalized Gaussian smoothing to its source density.

Let VVV be a finite-dimensional real inner-product space with its Borel measurable structure. Let ννν be a probability measure on VVV, and let ρ:V→Rρ : V → ℝρ:V→R satisfy IsBorellDensity ν volume ρ. For each real parameter sss, let normalizedDensity ρ s denote the normalized Gaussian-smoothed density. As sss tends to infinity through the real numbers,

∫V∣normalizedDensity⁡(ρ,s,x)−ρ(x)∣ dx⟶0.\int_V \left|\operatorname{normalizedDensity}(ρ,s,x)-ρ(x)\right|\,dx \longrightarrow 0.∫V​∣normalizedDensity(ρ,s,x)−ρ(x)∣dx⟶0.

The result supplies total-variation-type approximation at the density level and can be reused to compare integrals of bounded observables.

Original Lean declaration header

Within namespace FunctionalInequalities.KLS.LogConcave.GaussianSmoothing. Shown in its original module context. Proof omitted.

theorem normalizedDensity_tendsto_L1 {ν : Measure V}
    [IsProbabilityMeasure ν] {ρ : V → ℝ}
    (hρ : IsBorellDensity ν volume ρ) :
    Tendsto (fun s : ℝ => ∫ x : V, |normalizedDensity ρ s x - ρ x|)
      atTop (𝓝 0)

Module navigation

Module: KLS/LogConcave/Density/GaussianSmoothing/Approximation.

Definition modules: KLS/LogConcave/Density/GaussianSmoothing/Basic, KLS/LogConcave/Density/BorellRepresentation/Basic.

Supporting theorems: ae_continuous.

Next: smoothedLaw_integral_bounded_tendsto.

Source excerpt, lines 187–191 · Frozen source 408915f.

Preamble
import Definitions.Def_KLSModular_FunctionalInequalities_KLS_LogConcave_Density_GaussianSmoothing_Approximation

set_option autoImplicit false
open MeasureTheory Set Filter Topology Bornology
variable {V : Type*} [NormedAddCommGroup V] [InnerProductSpace ℝ V]
  [FiniteDimensional ℝ V] [MeasurableSpace V] [BorelSpace V]
Formal statement

theorem FunctionalInequalities.KLS.LogConcave.GaussianSmoothing.normalizedDensity_tendsto_L1_readable {ν : Measure V}
    [IsProbabilityMeasure ν] {ρ : V → ℝ}
    (hρ : IsBorellDensity ν volume ρ) :
    Tendsto (fun s : ℝ => ∫ x : V, |normalizedDensity ρ s x - ρ x|)
      atTop (𝓝 0) := by sorry
Source
Lean source: https://github.com/human-ai-mathematics/kls-lean/blob/408915f/formalization/FunctionalInequalities/KLS/LogConcave/Density/GaussianSmoothing/Approximation.lean#L184-L222 (repository human-ai-mathematics/kls-lean, commit 408915f, module `FunctionalInequalities.KLS.LogConcave.Density.GaussianSmoothing.Approximation`, declaration `FunctionalInequalities.KLS.LogConcave.GaussianSmoothing.normalizedDensity_tendsto_L1`; the repository is private at upload time).

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