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The Hlawka deficit of a candidate constant on a coordinate triple

Definition
HlawkaSchatten_DiagonalConstruction_Normalization

by savarin · Sep 28, 2026 · Mathlib 0df444a (Lean v4.33.1)

diagonal-constructionhlawka-deficithlawka-inequalityhlawka-schattennormalization

hlawkaDeficit packages the Hlawka inequality for the finite coordinate power functional and a candidate constant as a single real number, for vectors x,y,zx,y,zx,y,z indexed by an arbitrary finite type:

hlawkaDeficit⁡(p,K,x,y,z)=(2K−1)(∥x∥p+∥y∥p+∥z∥p)+∥x+y+z∥p−K(∥x+y∥p+∥x+z∥p+∥y+z∥p),\operatorname{hlawkaDeficit}(p,K,x,y,z) = (2K-1)\big(\|x\|_p+\|y\|_p+\|z\|_p\big) + \|x+y+z\|_p - K\big(\|x+y\|_p+\|x+z\|_p+\|y+z\|_p\big),hlawkaDeficit(p,K,x,y,z)=(2K−1)(∥x∥p​+∥y∥p​+∥z∥p​)+∥x+y+z∥p​−K(∥x+y∥p​+∥x+z∥p​+∥y+z∥p​),

using the finite coordinate power functional ∥⋅∥p\|\cdot\|_p∥⋅∥p​ (DiagonalConstruction.lpNorm), which is a norm for p≥1p\ge1p≥1. The definition itself accepts every real ppp.

Equivalently, by a theorem in the same source module, hlawkaDeficit⁡(p,K,x,y,z)\operatorname{hlawkaDeficit}(p,K,x,y,z)hlawkaDeficit(p,K,x,y,z) equals KKK times the pair-deficit sum minus the triple deficit for x,y,zx,y,zx,y,z (pairGapSum, tripleGap). So hlawkaDeficit⁡(p,K,x,y,z)≥0\operatorname{hlawkaDeficit}(p,K,x,y,z)\ge 0hlawkaDeficit(p,K,x,y,z)≥0 says exactly that the triple deficit for x,y,zx,y,zx,y,z is at most KKK times their pair-deficit sum, and a negative value witnesses a strict failure of that bound for the constant KKK.

This single real-valued packaging is what lets the theorems that accompany it manipulate a hypothetical failure algebraically: for K≥1K\ge1K≥1, relabeling — permuting x,y,zx,y,zx,y,z and, if needed, replacing xxx by −(x+y+z)-(x+y+z)−(x+y+z) — so that the total norm ∥x+y+z∥p\|x+y+z\|_p∥x+y+z∥p​ is at least as large as each of ∥x∥p,∥y∥p,∥z∥p\|x\|_p,\|y\|_p,\|z\|_p∥x∥p​,∥y∥p​,∥z∥p​, which can only decrease a negative deficit; and then, for p>0p>0p>0, rescaling so that ∥x∥p+∥y∥p+∥z∥p=1\|x\|_p+\|y\|_p+\|z\|_p=1∥x∥p​+∥y∥p​+∥z∥p​=1, which multiplies the deficit by a positive factor.

Definition code
import Definitions.Def_HlawkaSchatten_DiagonalConstruction_Basic
import Mathlib.Analysis.InnerProductSpace.Basic
import Mathlib.Analysis.InnerProductSpace.Dual
import Mathlib.Analysis.Normed.Lp.PiLp
import Mathlib.Analysis.SpecialFunctions.Pow.Continuity
import Mathlib.Tactic.Abel

/-
Copyright (c) 2026 Ezzeri Esa. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Ezzeri Esa
-/

/-! # Relabeling and normalization of a strict counterexample -/

namespace HlawkaSchatten.DiagonalConstruction

variable {ι : Type*} [Fintype ι]

/-- The target inequality with all terms moved to the nonnegative side. -/
noncomputable def hlawkaDeficit (p K : ℝ) (x y z : ι → ℝ) : ℝ :=
  (2 * K - 1) * (lpNorm p x + lpNorm p y + lpNorm p z) + lpNorm p (x + y + z) -
    K * (lpNorm p (x + y) + lpNorm p (x + z) + lpNorm p (y + z))



















end HlawkaSchatten.DiagonalConstruction
Source
https://github.com/savarin/hlawka-schatten/blob/79aa498bfcf7b22bd91d771fb32ec278e2d4704b/HlawkaSchatten/DiagonalConstruction/Normalization.lean#L15-L18
Human review
  • Endorsed by Shuze Chen · Sep 29, 2026

    Confirmed by the moderator at approval.

  • Endorsed by savarin · Sep 29, 2026

    Confirmed by the mission captain (proposal self-audit).

  • Endorsed by marwahaha · Sep 30, 2026

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