slug: grandjean-liang-bancal-brunner-gisin-2012-sliwa-seven-local-bound
bibkey: grandjean2012threesystems
doi: 10.1103/PhysRevA.85.052113
url: https://arxiv.org/abs/1204.3829v2
triage: theorem
motivation_gids:
  - D5/S3/QuantumBounds/SliwaSevenArbitraryOutcomeLocalBound.result

The local-bound clause of the Grandjean et al. conjecture on (B1)

Problem

B. Grandjean, Y.-C. Liang, J.-D. Bancal, N. Brunner and N. Gisin, “Bell inequalities for three systems and arbitrarily many measurement outcomes”, Physical Review A 85, 052113 (2012), arXiv:1204.3829v2, Appendix B, pp. 5–6, gives the arbitrary-output Sliwa seventh inequality (B1). It states that its local bound is numerically $6(K-1)$, attained by the all-zero deterministic strategy, and conjectures that both the local bound and the facet-defining property hold for every $K$. The settled statement is the local-bound clause:

$$\forall K\ge 2,\min \{J_K(a,b,c,A,B,C):a,b,c,A,B,C\in \mathbb{Z}/K\mathbb{Z}\}=6(K-1).$$

where $J_K$ is the twelve-term deterministic expression, with each bracket interpreted as the least nonnegative residue.

Motivation

The frozen declaration D5/S3/QuantumBounds/SliwaSevenArbitraryOutcomeLocalBound.result proves the local-bound clause for every natural $K\ge 2$. The source’s fact that deterministic strategies suffice reduces the local-theory minimum to this finite residue expression. The facet-defining clause is a separate question and remains outside this settlement.

Gap

Preregistration issue #12317 classified this as a Tier 1 published conjecture and recorded the source quotation and quantified target before Lean work. The paper’s arXiv v2 is the latest version. Bounded searches of the paper, its INSPIRE citing list, selected citing arXiv papers, MathDB, and the repository found no settlement in the searched scope. The unread citing literature and the completeness of those searches remain ASSUMED-UNVERIFIED; no worldwide priority claim is made.

Route

Write $s=[a+b+c{]}_K$, $t=[A+B+C{]}_K$, and $(u_1,u_2,u_3)=([-A+b+c{]}_K,[-B+a+c{]}_K,[-C+a+b{]}_K)$. The remaining mixed residues are $v_i=[u_i+t-s{]}_K$. Their integer sum has the form $u_1+u_2+u_3=2s-t+Kq$. Splitting on $t\ge s$ or $s>t$, and on which residues wrap, gives the lower bounds for the mixed sum, including the strengthened $s=0<t$ case. The exact residue identity then yields $J_K\ge 6(K-1)$. The all-zero assignment gives equality.

Falsifier

A counterexample would be a natural $K\ge 2$ and six values in $\mathbb{Z}/K\mathbb{Z}$ whose twelve-term value is below $6(K-1)$. Changing the residue convention, the six mixed permutation terms, or the quantifier $K\ge 2$ would define a different question.

Evidence

The complete kernel-checked proof is the public declaration result in D5/S3/QuantumBounds/SliwaSevenArbitraryOutcomeLocalBound.lean. The public surface contains the expression definition J, the claim definition claim, and the settling theorem result; no helper theorem is exported. The frozen statement identity is sha256:9f25c437c0f4db64a7b4695d203db1692f60a2fbb9ddaf714a67cd5a0af3dded. The Freeze event is sha256:b15faf9038569a21ae48d8ff2f1e6d69a7a89c9f50cf070262fd7f5df7c4b3b7. The event has no project-level frozen prerequisites. The proof uses only propext, Classical.choice, and Quot.sound; it introduces no axiom, sorry, or native_decide.

Triage

Tier 1 published conjecture; resolution Proved for the local-bound clause of (B1), via D5/S3/QuantumBounds/SliwaSevenArbitraryOutcomeLocalBound.result. The facet-defining property, quantum optimum, and visibility optimum are outside the result. The theorem is bind-only after the private residue helper is inlined; its admission basis is open-problem-resolution (#12317; Proved). Escape registration is paused under CLAUDE.md §3.9.

What the settlement shows

• Proved in this module: the deterministic minimum of (B1) is exactly $6(K-1)$ for every $K\ge 2$, uniformly in $K$.
• Mechanism: the residue decomposition controls all six mixed terms and handles the only negative correction in the exact identity; the all-zero strategy is sharp.
• Scope that remains open: whether (B1) is facet-defining for every $K$, and any quantum or visibility optimization, are not settled here.
• Source consequences: the paper’s local-theory comparison for (B1) may use $6(K-1)$ for all $K$; claims depending on the separate facet conjecture remain conditional.

Computed attaining strategies for small K

Exact integer enumeration of all $K^6$ ordered deterministic strategies $(a,b,c,A,B,C)\in \{0,\dots ,K-1{\}}^6$ for each $K=2,\dots ,7$ gives the following computed, not proved readings. Each of the twelve terms of $J_K$ is evaluated using the least nonnegative integer remainder; every strategy is visited, without symmetry reduction.

Thus the computed minimum equals $6(K-1)$ throughout this computation range. These finite readings are separate from the module’s all-$K$ proof of the minimum.

To describe which enumerated strategies attain it, write $S=[a+b+c{]}_K$, $T=[A+B+C{]}_K$, $(u_1,u_2,u_3)=([-A+b+c{]}_K,[-B+a+c{]}_K,[-C+a+b{]}_K)$, and $L={\sum }_{i=1}^3(u_i+[u_i+T-S{]}_K)$. In the enumeration, attainment agrees exactly with

$$L=S+T+K(1_{S=0}-1_{T=0}).$$

This is a computed classification for $K=2,\dots ,7$, checked against the direct twelve-term evaluation for every strategy, not a new proved classification theorem. In that range the attaining strategies occupy three regimes: $S=T=0$ with $L=0$; $S=0<T$ with $L=T+K$; and $S,T>0$ with $L=S+T$. No enumerated attaining strategy has $T=0<S$. For every enumerated $K$, computed representatives of the three regimes are respectively $(0,0,0,0,0,0)$, $(0,0,0,0,0,1)$, and $(0,0,1,0,1,0)$. At $K=2$, the computed $(S,T)$ class counts are $(0,0):4$, $(0,1):16$, and $(1,1):12$. Attainment in the computed range is therefore not confined to $S=T=0$ or to the all-zero assignment.

The computed count pattern for $K=2,\dots ,7$ is

$$N_K=K^2\left(\left(\genfrac{}{}{0ex}{}{K+3}{4}\right)+3(K-1)\right).$$

Fitting the normalized counts $N_K/K^2$ for $K=2,\dots ,6$ gives the quartic $K^4/24+K^3/4+11K^2/24+13K/4-3$, equal to the parenthesized expression. That fit predicts $11172$ attaining strategies at the held-out $K=7$, matching its exact enumeration. The count formula is open in general; the finite agreement is computed evidence, not a theorem.

ASSUMED-UNVERIFIED

The literature search was bounded to the sources and queries recorded in issue #12317. Several citing papers were not read in full, and no exhaustive literature or priority claim is made. The Lean kernel verifies the encoded residue statement and its axiom closure; the correspondence to the paper’s full probabilistic notation uses the source’s deterministic strategy reduction.