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Lemma 8, p. 22 — if M(p, q, r) ⪰ 0 and q ≤ 0, then p ≥ −√3/2

Proved
QMCProduct.HalfApprox.lemma_8

by mikedeng1 · Oct 21, 2026 · Mathlib 0df444a (Lean v4.33.1)

monogamy-of-entanglementp2o-batch-pfp2ap2o-gran-per-chapterp2o-plan-paperp2o-v1quantum-informationsemidefinite-programming

Let M(p,q,r)M(p,q,r)M(p,q,r) be the real 4×44\times44×4 SWAP Gram matrix displayed in Section 4.3. If M(p,q,r)M(p,q,r)M(p,q,r) is positive semidefinite and q≤0q\le0q≤0, then

p≥−32.p\ge-\frac{\sqrt3}{2}.p≥−23​​.

The bound rules out a sufficiently negative SWAP value on one edge alongside a nonpositive value on an adjacent edge.

Formalization Note The statement follows the printed lemma. The proof's displayed dual certificate has a coordinate-order erratum, recorded in the moderation notes.

Preamble
import Definitions.Def_QMCProduct_HalfApprox_Basic

set_option autoImplicit false
Formal statement
namespace QMCProduct.HalfApprox

/-- Lemma 8, p. 22. -/
theorem lemma_8 (p q r : ℝ) (hM : (swapGram p q r).PosSemidef) (hq : q ≤ 0) :
    -(Real.sqrt 3) / 2 ≤ p := by sorry

end QMCProduct.HalfApprox
Source
Parekh & Thompson, An Optimal Product-State Approximation for 2-Local Quantum Hamiltonians with Positive Terms, arXiv:2206.08342v2, p. 22, Lemma 8
Human review
  • Endorsed by Shuze Chen · Oct 21, 2026

    Confirmed by the moderator at approval.

  • Endorsed by mikedeng1 · Oct 21, 2026

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

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