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Convergence of Truncated Laplace Derivatives

Proved
FunctionalInequalities.Analysis.BakryEmery.tendsto_iteratedFDeriv_laplace_cond_closedBall_readable

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

functional-inequalitieskls-conjecturekls-modularkls-readablelog-concave

This statement proves convergence of the iterated derivatives of Laplace transforms of ball-conditioned measures.

Let EEE be a finite-dimensional real inner-product space with its Borel measurable structure, and let ν\nuν be a probability measure on EEE. Let r>0r>0r>0 and assume

∫er∥x∥ dν(x)<∞.\int e^{r\|x\|}\,d\nu(x)<\infty.∫er∥x∥dν(x)<∞.

For each d∈Nd\in\mathbb Nd∈N, define the Laplace transform of the conditional measure on the closed ball B‾(0,R)\overline B(0,R)B(0,R) by

LR(z)=∫e⟨z,x⟩ d(ν[∣B‾(0,R)])(x),L_R(z)=\int e^{\langle z,x\rangle}\,d\bigl(\nu[\mid\overline B(0,R)]\bigr)(x),LR​(z)=∫e⟨z,x⟩d(ν[∣B(0,R)])(x),

and let L(z)=∫e⟨z,x⟩ dν(x)L(z)=\int e^{\langle z,x\rangle}\,d\nu(x)L(z)=∫e⟨z,x⟩dν(x). Then, as R→∞R\to\inftyR→∞ through natural numbers,

DdLR(0)⟶DdL(0).D^dL_R(0)\longrightarrow D^dL(0).DdLR​(0)⟶DdL(0).

Here convergence is in the norm of the corresponding iterated derivative spaces. This is the moment-tensor convergence statement used in truncation arguments for cumulants.

Original Lean declaration header

Within namespace FunctionalInequalities.Analysis.BakryEmery. Shown in its original module context. Proof omitted.

theorem tendsto_iteratedFDeriv_laplace_cond_closedBall (ν : Measure E) [IsProbabilityMeasure ν]
    {r : ℝ} (hr : 0 < r) (hexp : Integrable (fun x => Real.exp (r * ‖x‖)) ν) (d : ℕ) :
    Tendsto (fun R : ℕ => iteratedFDeriv ℝ d
        (fun z => ∫ x, Real.exp ⟪z, x⟫ ∂(ν[|Metric.closedBall (0 : E) R])) 0) atTop
      (𝓝 (iteratedFDeriv ℝ d (fun z => ∫ x, Real.exp ⟪z, x⟫ ∂ν) 0))

Module navigation

Module: Analysis/BakryEmery/Cumulant/Truncation.

Supporting theorems: norm_iteratedFDeriv_laplace_cond_sub_le.

Previous: norm_iteratedFDeriv_laplace_cond_sub_le · Next: cumulant_eq_taylorComp_cond.

Source excerpt, lines 118–122 · Frozen source 408915f.

Preamble
import Definitions.Def_KLSModular_FunctionalInequalities_Analysis_BakryEmery_Cumulant_Truncation

open MeasureTheory ProbabilityTheory Filter Topology
open scoped RealInnerProductSpace ContDiff
variable {E : Type*} [NormedAddCommGroup E] [InnerProductSpace ℝ E]
  [FiniteDimensional ℝ E] [MeasurableSpace E] [BorelSpace E]
Formal statement

theorem FunctionalInequalities.Analysis.BakryEmery.tendsto_iteratedFDeriv_laplace_cond_closedBall_readable (ν : Measure E) [IsProbabilityMeasure ν]
    {r : ℝ} (hr : 0 < r) (hexp : Integrable (fun x => Real.exp (r * ‖x‖)) ν) (d : ℕ) :
    Tendsto (fun R : ℕ => iteratedFDeriv ℝ d
        (fun z => ∫ x, Real.exp ⟪z, x⟫ ∂(ν[|Metric.closedBall (0 : E) R])) 0) atTop
      (𝓝 (iteratedFDeriv ℝ d (fun z => ∫ x, Real.exp ⟪z, x⟫ ∂ν) 0)) := by sorry
Source
Lean source: https://github.com/human-ai-mathematics/kls-lean/blob/408915f/formalization/FunctionalInequalities/Analysis/BakryEmery/Cumulant/Truncation.lean#L117-L155 (repository human-ai-mathematics/kls-lean, commit 408915f, module `FunctionalInequalities.Analysis.BakryEmery.Cumulant.Truncation`, declaration `FunctionalInequalities.Analysis.BakryEmery.tendsto_iteratedFDeriv_laplace_cond_closedBall`; the repository is private at upload time).

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