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GHZ certificate (3 parties)

Enter the 4 correlators ⟨XXX⟩, ⟨XYY⟩, ⟨YXY⟩, ⟨YYX⟩ from your 3-party experiment. The certifier computes the Mermin value M = ⟨XXX⟩−⟨XYY⟩−⟨YXY⟩−⟨YYX⟩ and classifies: local (|M| ≤ 2), super-classical (up to 4), or — in the exact case (+1,−1,−1,−1) — the deterministic GHZ paradox: a local model is impossible with probability 1, not merely improbable.