Endpoint Measurability of Polarized Increments

Proved

LevyStochCalc.Brownian.Ito.stronglyMeasurable_polarQuadVarIncrement_readable

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

functional-inequalitieskls-conjecturekls-modularkls-readablelog-concavevendored-levystochcalc

Let $H_1,H_2$ satisfy the stated measurability, progressive-measurability, and joint square-integrability assumptions. For any $a\le b$ , the function

\omega\longmapsto\mathrm{polarQuadVarIncrement}_{a,b}(H_1,H_2)(\omega)

is strongly measurable with respect to the right-continuous sigma-algebra $\mathcal F.\mathrm{rightCont}_b$ . No positivity or boundedness assumption on the integrands is required in this measurability statement.

Original Lean declaration header

Within namespace LevyStochCalc.Brownian.Ito. Shown in its original module context. Proof omitted.

theorem stronglyMeasurable_polarQuadVarIncrement {a b : ℝ} (hab : a ≤ b) :
    @MeasureTheory.StronglyMeasurable Ω ℝ _ (ℱ.rightCont b)
      (polarQuadVarIncrement W ℱ hℱ H₁ H₂ hm₁ hm₂ hp₁ hp₂ hq₁ hq₂ a b)

Module navigation

Module: LevyStochCalc/Brownian/PolarisedQuadVar.

Definition modules: LevyStochCalc/Brownian/Filtered, LevyStochCalc/Brownian/Construction, LevyStochCalc/Probability/Progressive.

Previous: condExp_polarQuadVarIncrement · Next: integral_sq_polarQuadVarIncrement_le.

Source excerpt, lines 209–211 · Frozen source 408915f.

Preamble

import Definitions.Def_KLSModular_LevyStochCalc_Brownian_PolarisedQuadVar

/-
Copyright (c) 2026 Christian Garry. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Christian Garry
-/
-- Vendored from https://github.com/cgarryZA/LevyStochCalc at commit 984dbf0b790031eac05d56fe5a84b65e15e1e932 (upstream path LevyStochCalc/Brownian/PolarisedQuadVar.lean; Apache-2.0; provenance in formalization/vendor/vendor-lock.json of the KLS repository)
open scoped NNReal ENNReal
universe u
variable {Ω : Type u} [MeasurableSpace Ω]
variable {P : MeasureTheory.Measure Ω} [MeasureTheory.IsProbabilityMeasure P] (W : LevyStochCalc.Brownian.BrownianMotion P)
  (ℱ : MeasureTheory.Filtration ℝ ‹MeasurableSpace Ω›) (hℱ : LevyStochCalc.Brownian.IsBrownianFiltration W ℱ)
  (H₁ H₂ : Ω → ℝ → ℝ)
  (hm₁ : Measurable (Function.uncurry H₁)) (hm₂ : Measurable (Function.uncurry H₂))
  (hp₁ : LevyStochCalc.Probability.ProgressivelyMeasurable ℱ H₁)
  (hp₂ : LevyStochCalc.Probability.ProgressivelyMeasurable ℱ H₂)
  (hq₁ : ∀ T, 0 < T → ∫⁻ ω, ∫⁻ s in Set.Icc (0 : ℝ) T,
    (‖H₁ ω s‖₊ : ℝ≥0∞) ^ 2 ∂MeasureTheory.MeasureSpace.volume ∂P < ⊤)
  (hq₂ : ∀ T, 0 < T → ∫⁻ ω, ∫⁻ s in Set.Icc (0 : ℝ) T,
    (‖H₂ ω s‖₊ : ℝ≥0∞) ^ 2 ∂MeasureTheory.MeasureSpace.volume ∂P < ⊤)
  (hma : Measurable (Function.uncurry fun ω s => H₁ ω s + H₂ ω s))
  (hpa : LevyStochCalc.Probability.ProgressivelyMeasurable ℱ fun ω s => H₁ ω s + H₂ ω s)
  (hqa : ∀ T, 0 < T → ∫⁻ ω, ∫⁻ s in Set.Icc (0 : ℝ) T,
    (‖H₁ ω s + H₂ ω s‖₊ : ℝ≥0∞) ^ 2 ∂MeasureTheory.MeasureSpace.volume ∂P < ⊤)
include hℱ

Formal statement


theorem LevyStochCalc.Brownian.Ito.stronglyMeasurable_polarQuadVarIncrement_readable {a b : ℝ} (hab : a ≤ b) :
    @MeasureTheory.StronglyMeasurable Ω ℝ _ (ℱ.rightCont b)
      (polarQuadVarIncrement W ℱ hℱ H₁ H₂ hm₁ hm₂ hp₁ hp₂ hq₁ hq₂ a b) := by sorry

Source

Lean source: https://github.com/cgarryZA/LevyStochCalc/blob/984dbf0b790031eac05d56fe5a84b65e15e1e932/LevyStochCalc/Brownian/PolarisedQuadVar.lean#L206-L226 (repository human-ai-mathematics/kls-lean, commit 408915f, module `LevyStochCalc.Brownian.PolarisedQuadVar`, declaration `LevyStochCalc.Brownian.Ito.stronglyMeasurable_polarQuadVarIncrement`; the repository is private at upload time). Vendored from https://github.com/cgarryZA/LevyStochCalc at commit 984dbf0b790031eac05d56fe5a84b65e15e1e932 (Apache-2.0; upstream copyright notice retained in the Lean text).

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