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A uniform bound for the Cauchy transform of compactly supported LpL^pLp data, p>2p>2p>2

Proved
JHolomorphic.norm_integral_inv_sub_smul_le

by Mazecto · Oct 22, 2026 · Mathlib 0df444a (Lean v4.33.1)

elliptic-regularitypseudoholomorphic-curvessobolev-spaces

Let 2<p<∞2<p<\infty2<p<∞, R>0R>0R>0 and let EEE be a complex normed space. There is a constant C≥0C\ge0C≥0 such that for every g∈Lp(C;E)g\in L^p(\mathbb C;E)g∈Lp(C;E) vanishing outside the open disc BR(0)B_R(0)BR​(0) and every z∈BR(0)z\in B_R(0)z∈BR​(0), the map ζ↦(z−ζ)−1g(ζ)\zeta\mapsto(z-\zeta)^{-1}g(\zeta)ζ↦(z−ζ)−1g(ζ) is Lebesgue integrable on C\mathbb CC and

∥∫Cg(ζ)z−ζ dζ∥≤C ∥g∥Lp(C).\Big\|\int_{\mathbb C}\frac{g(\zeta)}{z-\zeta}\,d\zeta\Big\|\le C\,\|g\|_{L^p(\mathbb C)}.​∫C​z−ζg(ζ)​dζ​≤C∥g∥Lp(C)​.

This is the uniform bound for the Cauchy transform of compactly supported LpL^pLp data, p>2p>2p>2, used to build local solutions of Cauchy–Riemann type equations.

Formalization Note g:C→Eg:\mathbb C\to Eg:C→E with MemLp g (ENNReal.ofReal p) volume and Function.support g ⊆ ball 0 R; the integrand is (z - ζ)⁻¹ • g ζ (complex scalar multiplication), and the bound is ‖∫ ζ, (z - ζ)⁻¹ • g ζ‖ ≤ C * (eLpNorm g (ENNReal.ofReal p) volume).toReal.

Preamble
import Definitions.Def_JHolomorphic_Setting
import Mathlib.MeasureTheory.Function.LpSeminorm.CompareExp
import Mathlib.MeasureTheory.Constructions.HaarToSphere
import Mathlib.MeasureTheory.Measure.Lebesgue.Complex
import Mathlib.MeasureTheory.Measure.Lebesgue.EqHaar
import Mathlib.MeasureTheory.Measure.Haar.Unique
import Mathlib.MeasureTheory.Group.Measure
import Mathlib.Analysis.SpecialFunctions.Integrability.Basic
import Mathlib.LinearAlgebra.Complex.FiniteDimensional
Formal statement
namespace JHolomorphic

open MeasureTheory Metric Filter Topology Set
open scoped ContDiff ENNReal NNReal

/-- Let `2 < p < ∞` and `R > 0`. There is `C ≥ 0` such that for every `g ∈ L^p(ℂ; E)` vanishing
outside the disc `B_R(0)` and every `z ∈ B_R(0)`, the map `ζ ↦ (z - ζ)⁻¹ g(ζ)` is integrable and
`‖∫ (z - ζ)⁻¹ g(ζ) dζ‖ ≤ C ‖g‖_{L^p}`. -/
theorem norm_integral_inv_sub_smul_le {E : Type*} [NormedAddCommGroup E] [NormedSpace ℂ E]
    (p R : ℝ) (hp : 2 < p) (hR : 0 < R) :
    ∃ C : ℝ, 0 ≤ C ∧ ∀ g : ℂ → E, MemLp g (ENNReal.ofReal p) volume →
      Function.support g ⊆ ball 0 R → ∀ z ∈ ball (0 : ℂ) R,
        Integrable (fun ζ => (z - ζ)⁻¹ • g ζ) ∧
        ‖∫ ζ, (z - ζ)⁻¹ • g ζ‖ ≤ C * (eLpNorm g (ENNReal.ofReal p) volume).toReal := by
  sorry

end JHolomorphic
Source
Standard estimate for the Cauchy transform; used for C. Wendl, Lectures on Symplectic Field Theory, arXiv:1612.01009, Lecture 2, Lemma 2.24

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