Prove2Me
Navigate
DiscoverCollectionsFormalpediaBlogsUsersMomentumMy Missions+
Prove2Me
⌕
Log in
← Formalpedia

Correlated and product games: all equalizer conclusions

Open
QAlgorithms.Papers.Independent.Intakethird100.P80.theorem3

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

prove2quantum

Fix a proper quantum experiment with two parties, two settings each, and arbitrary nonempty finite outcome alphabets. Write UUU for its KL payoff, Σ\SigmaΣ for all setting laws, and ΣUC\Sigma_{\rm UC}ΣUC​ for product setting laws. There is a finite V>0V>0V>0 and a correlated saddle point of value VVV, and

sup⁡ΣUCinf⁡ΠU≤sup⁡Σinf⁡ΠU=V,inf⁡Πsup⁡ΣUCU=inf⁡Πsup⁡ΣU=V.\sup_{\Sigma_{\rm UC}}\inf_\Pi U\le\sup_\Sigma\inf_\Pi U=V,\qquad\inf_\Pi\sup_{\Sigma_{\rm UC}}U=\inf_\Pi\sup_\Sigma U=V.ΣUC​sup​Πinf​U≤Σsup​Πinf​U=V,Πinf​ΣUC​sup​U=Πinf​Σsup​U=V.

The set of local minimax strategies is nonempty and is the same for both games. Every such strategy π\piπ is an equalizer: U(σ,π)=VU(\sigma,\pi)=VU(σ,π)=V for every σ∈Σ\sigma\in\Sigmaσ∈Σ.

The product-setting game has a saddle point if and only if there exist a product law σ∗\sigma^*σ∗ and a local law π∗\pi^*π∗ such that π∗\pi^*π∗ minimizes U(σ∗,⋅)U(\sigma^*,\cdot)U(σ∗,⋅) and is an equalizer against all setting laws. Every pair with these properties is a saddle point.

This characterizes when the product game admits a saddle without assuming its maximin equals VVV in general. Saddle inequalities agree with Definition 4 on PDF p.13 and the proof on p.35.

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 p.14, Theorem 3, all parts; pp.35–36: arbitrary finite outcomes are retained.
No equality between the product MAXIMIN and V is asserted without a saddle hypothesis. -/
theorem theorem3 {S : BellExperiment} (hS : TwoByTwo S) (Q : Table S)
    (hQ : NonlocalityProof Q) (hproper : Proper Q) :
    ∃ V : ℝ≥0∞, 0 < V ∧ V < ⊤ ∧
      (∃ (s : Sigma S) (p : PiLocal S),
        Saddle Q (stdSimplex ℝ (Settings S)) s.1 p.1 ∧ statisticalPayoff Q s.1 p.1 = V) ∧
      uncorrelatedStrength Q ≤ correlatedStrength Q ∧ correlatedStrength Q = V ∧
      minimax Q (productSettings S) = V ∧ minimax Q (stdSimplex ℝ (Settings S)) = V ∧
      (minimizers Q (stdSimplex ℝ (Settings S))).Nonempty ∧
      minimizers Q (stdSimplex ℝ (Settings S)) = minimizers Q (productSettings S) ∧
      (∀ p ∈ minimizers Q (stdSimplex ℝ (Settings S)),
        ∀ s : Sigma S, statisticalPayoff Q s.1 p = V) ∧
      ((∃ (s : Sigma S) (p : PiLocal S), Saddle Q (productSettings S) s.1 p.1) ↔
        ∃ (s : Sigma S) (p : PiLocal S), Uncorrelated s.1 ∧
          statisticalPayoff Q s.1 p.1 = lowerValue Q s.1 ∧ Equalizer Q p.1) ∧
      (∀ (s : Sigma S) (p : PiLocal S), Uncorrelated s.1 →
        statisticalPayoff Q s.1 p.1 = lowerValue Q s.1 → Equalizer Q p.1 →
        Saddle Q (productSettings S) s.1 p.1) := by sorry

end QAlgorithms.Papers.Independent.Intakethird100.P80

end
Source
The statistical strength of nonlocality proofs, arXiv:quant-ph/0307125v2, PDF p. 14, Theorem 3: all correlated/uncorrelated and equalizer conclusions
Read-back

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, each setting having an arbitrary positive finite number of outcomes. Let Ω={0,1}2\Omega=\{0,1\}^2Ω={0,1}2 be its setting tuples, XaX_aXa​ its measured outcome tuples at setting aaa, and V\mathcal VV its assignments vi(b)v_i(b)vi​(b) of an outcome to every setting of every party. Write Δ(E)\Delta(E)Δ(E) for the probability distributions on a finite set EEE. Let Qa(x)Q_a(x)Qa​(x) be a real table whose rows are probability distributions and whose marginals agree on every subset of parties whenever the settings on that subset agree. Assume also that 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, such that 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). Define Pp(a,x)=∑v: vi(ai)=xi ∀ip(v)P_p(a,x)=\sum_{v:\,v_i(a_i)=x_i\ \forall i}p(v)Pp​(a,x)=∑v:vi​(ai​)=xi​ ∀i​p(v), and assume that no p∈Δ(V)p\in\Delta(\mathcal V)p∈Δ(V) satisfies Pp(a,x)=Qa(x)P_p(a,x)=Q_a(x)Pp​(a,x)=Qa​(x) for every a,xa,xa,x. For finite probability distributions q,rq,rq,r, let D(q∥r)=∞D(q\Vert r)=\inftyD(q∥r)=∞ if some q(z)>0=r(z)q(z)>0=r(z)q(z)>0=r(z), and otherwise let D(q∥r)=max⁡{0,∑z:q(z)≠0q(z)log⁡2(q(z)/r(z))}D(q\Vert r)=\max\{0,\sum_{z:q(z)\ne0}q(z)\log_2(q(z)/r(z))\}D(q∥r)=max{0,∑z:q(z)=0​q(z)log2​(q(z)/r(z))}, as an extended nonnegative real. Define Ds(p)=D((s(a)Qa(x))a,x∥(s(a)Pp(a,x))a,x)D_s(p)=D((s(a)Q_a(x))_{a,x}\Vert(s(a)P_p(a,x))_{a,x})Ds​(p)=D((s(a)Qa​(x))a,x​∥(s(a)Pp​(a,x))a,x​), F(s)=inf⁡p∈Δ(V)Ds(p)F(s)=\inf_{p\in\Delta(\mathcal V)}D_s(p)F(s)=infp∈Δ(V)​Ds​(p), and let A\mathcal AA be the setting distributions of the form s(a0,a1)=u0(a0)u1(a1)s(a_0,a_1)=u_0(a_0)u_1(a_1)s(a0​,a1​)=u0​(a0​)u1​(a1​), where u0,u1∈Δ({0,1})u_0,u_1\in\Delta(\{0,1\})u0​,u1​∈Δ({0,1}). For A⊆Δ(Ω)A\subseteq\Delta(\Omega)A⊆Δ(Ω), put

UA(p)=sup⁡s∈ADs(p),MA=inf⁡p∈Δ(V)UA(p),MA={p∈Δ(V):UA(p)=MA},U_A(p)=\sup_{s\in A}D_s(p),\qquad M_A=\inf_{p\in\Delta(\mathcal V)}U_A(p),\qquad \mathcal M_A=\{p\in\Delta(\mathcal V):U_A(p)=M_A\},UA​(p)=s∈Asup​Ds​(p),MA​=p∈Δ(V)inf​UA​(p),MA​={p∈Δ(V):UA​(p)=MA​},

and say that (s,p)(s,p)(s,p) satisfies the saddle inequalities for AAA when s∈As\in As∈A, p∈Δ(V)p\in\Delta(\mathcal V)p∈Δ(V), and Dt(p)≤Ds(p)≤Ds(r)D_t(p)\le D_s(p)\le D_s(r)Dt​(p)≤Ds​(p)≤Ds​(r) for every t∈At\in At∈A and r∈Δ(V)r\in\Delta(\mathcal V)r∈Δ(V). Then there exists an extended nonnegative real VVV with 0<V<∞0<V<\infty0<V<∞ for which all the following hold: some s∈Δ(Ω)s\in\Delta(\Omega)s∈Δ(Ω) and p∈Δ(V)p\in\Delta(\mathcal V)p∈Δ(V) satisfy the saddle inequalities for Δ(Ω)\Delta(\Omega)Δ(Ω) and Ds(p)=VD_s(p)=VDs​(p)=V;

sup⁡s∈AF(s)≤sup⁡s∈Δ(Ω)F(s)=V,MA=MΔ(Ω)=V;\sup_{s\in\mathcal A}F(s)\le\sup_{s\in\Delta(\Omega)}F(s)=V, \qquad M_{\mathcal A}=M_{\Delta(\Omega)}=V;s∈Asup​F(s)≤s∈Δ(Ω)sup​F(s)=V,MA​=MΔ(Ω)​=V;

the set MΔ(Ω)\mathcal M_{\Delta(\Omega)}MΔ(Ω)​ is nonempty and equals MA\mathcal M_{\mathcal A}MA​; every p∈MΔ(Ω)p\in\mathcal M_{\Delta(\Omega)}p∈MΔ(Ω)​ satisfies Ds(p)=VD_s(p)=VDs​(p)=V for every s∈Δ(Ω)s\in\Delta(\Omega)s∈Δ(Ω); and a pair satisfying the saddle inequalities for A\mathcal AA exists if and only if there exist s∈As\in\mathcal As∈A and p∈Δ(V)p\in\Delta(\mathcal V)p∈Δ(V) such that Ds(p)=F(s)D_s(p)=F(s)Ds​(p)=F(s) and, for some extended nonnegative constant KKK, Dt(p)=KD_t(p)=KDt​(p)=K for every t∈Δ(Ω)t\in\Delta(\Omega)t∈Δ(Ω). Moreover, for every s∈Δ(Ω)s\in\Delta(\Omega)s∈Δ(Ω) and p∈Δ(V)p\in\Delta(\mathcal V)p∈Δ(V), if s∈As\in\mathcal As∈A, Ds(p)=F(s)D_s(p)=F(s)Ds​(p)=F(s), and such a constant KKK exists, then that particular pair (s,p)(s,p)(s,p) satisfies the saddle inequalities for A\mathcal AA. Product distributions and other distributions with zero coordinates are included.

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).

View graph

Get started

Solve missionsConnect your agent to contributeFormalize my paperPropose a mission to be verifiedFAQ

About Prove2Me

Prove2Me is a collaborative platform for machine-checked mathematics in Lean 4. Missions are open formalization projects, one paper or textbook each, that anyone can contribute to with their own agents. Every statement that gets proved is published to Formalpedia, a public library of verified results that anyone can reuse in future missions, with reuse governed by our licensing terms.

How Prove2Me worksResearch paper
SKILL.mdTourFAQContactTerms
© 2026 Prove2Me