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One local law matches any three setting pairs

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QAlgorithms.Papers.Independent.Intakethird100.P80.lemma1

by Gohan · Nov 1, 2026 · Mathlib 0df444a (Lean v4.33.1)

prove2quantum

Fix a normalized quantum-generated no-signalling experiment with two parties, two settings per party, and arbitrary nonempty finite outcome alphabets. For any omitted joint setting s0s_0s0​, there is one probability law π\piπ on the full tuple of potential outcomes such that

Ps;π=Qsfor every s≠s0.P_{s;\pi}=Q_s\qquad\text{for every }s\ne s_0.Ps;π​=Qs​for every s=s0​.

Thus all three remaining outcome laws are reproduced simultaneously by the same local theory. No-signalling consistency is retained, and no condition is imposed on the omitted marginal.

Preamble
import Definitions.Def_QAlgorithms_Papers_Independent_Intakethird100_P80
Formal statement
noncomputable section

namespace QAlgorithms.Papers.Independent.Intakethird100.P80

open scoped BigOperators ENNReal Topology Classical

open MeasureTheory Filter

/-- PDF pp.31–32, Lemma 1, including its extension to more than two outcomes.
One common local law fits the three retained settings simultaneously. -/
theorem lemma1 {S : BellExperiment} (hS : TwoByTwo S) (Q : Table S)
    (hQ : NonlocalityProof Q) (omitted : Settings S) :
    ∃ p : PiLocal S, ∀ s : Settings S, s ≠ omitted → localTable p.1 s = Q s := by sorry

end QAlgorithms.Papers.Independent.Intakethird100.P80

end
Source
The statistical strength of nonlocality proofs, arXiv:quant-ph/0307125v2, PDF p. 31, Lemma 1: local compatibility of any three setting pairs
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What the Lean code literally says, in plain math · gpt-6.1-sol

Let SSS be a Bell experiment with exactly two parties and exactly two settings per party, with a positive finite number of outcomes at every setting. A setting tuple is a=(a0,a1)∈{0,1}2a=(a_0,a_1)\in\{0,1\}^2a=(a0​,a1​)∈{0,1}2, an outcome tuple at aaa belongs to the product XaX_aXa​ of the two corresponding outcome sets, and a potential assignment v∈Vv\in\mathcal Vv∈V chooses an outcome vi(b)v_i(b)vi​(b) for each party iii and each of its settings bbb. Let Qa(x)Q_a(x)Qa​(x) be a real table whose rows are nonnegative and sum to 111, whose marginal probabilities on any subset of parties agree whenever the settings on that subset agree, and for which there exist positive local dimensions, a positive semidefinite joint matrix ρ\rhoρ of trace 111, and positive semidefinite local measurement matrices Mi,b,uM_{i,b,u}Mi,b,u​ summing to the identity over uuu, with Qa(x)=Re⁡tr⁡((M0,a0,x0⊗M1,a1,x1)ρ)Q_a(x)=\operatorname{Re}\operatorname{tr}((M_{0,a_0,x_0}\otimes M_{1,a_1,x_1})\rho)Qa​(x)=Retr((M0,a0​,x0​​⊗M1,a1​,x1​​)ρ). For every specified setting tuple o∈{0,1}2o\in\{0,1\}^2o∈{0,1}2, there exists a function p:V→Rp:\mathcal V\to\mathbb Rp:V→R with p(v)≥0p(v)\ge0p(v)≥0 for every vvv and ∑vp(v)=1\sum_v p(v)=1∑v​p(v)=1, such that for every setting tuple a≠oa\ne oa=o and every x∈Xax\in X_ax∈Xa​,

∑v∈Vv0(a0)=x0, v1(a1)=x1p(v)=Qa(x).\sum_{\substack{v\in\mathcal V\\v_0(a_0)=x_0,\ v_1(a_1)=x_1}}p(v)=Q_a(x).v∈Vv0​(a0​)=x0​, v1​(a1​)=x1​​∑​p(v)=Qa​(x).

There is no condition on this equality at the specified tuple ooo; agreement there is also permitted.

Human review
  • Endorsed by Shuze Chen · Nov 1, 2026

    Confirmed by the moderator at approval.

  • Endorsed by Gohan · Nov 1, 2026

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

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