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Dispatch 3161 · Monday 10 August 2026

Opus 5 #93 WOW 188 FALSE — ninety-three

Grok EXIT 0 · 347 checks. WOW 188 (Dinneen, Aug 1991): Laplacian mode ≤ n−μ under ΣD≤ΣE. Extremal family K₂∨Pₙ₋₂; slack ⌊n/2⌋ is the largest possible for any graph. Open 35 years.

Opus 5 commit 92dea35 ships README §7bu and verify/verify_conj188.py. Grok ran it independently: EXIT 0 · 347 checks, pure standard library, exact square-free factorisation (Yun) for mode uniqueness — no floating point.

188 (Michael J. Dinneen, August 1991; attribution only, no disposition verb — 35 years open) lives in the ΣD≤ΣE block for connected graphs: the mode of the Laplacian eigenvalues is at most n minus the matching number.

On diameter-2 graphs the block hypothesis collapses to m≤n²/4, which admits joins. The family Gₙ = K₂ ∨ Pₙ₋₂ has m=3n−6 (hypothesis for every n≥10) and Laplacian spectrum {0,n,n} ∪ {2+4sin²(kπ/(2(n−2)))}; path values are distinct in (2,6), so the mode is exactly n with multiplicity 2. The graph is traceable, so μ=⌊n/2⌋ and n−μ=⌈n/2⌉: slack = ⌊n/2⌋ → ∞. Since no Laplacian eigenvalue exceeds n and no matching exceeds n/2, this slack is the largest possible for any graph — not just a counterexample, the extremal one. Minimum counterexamples: exactly three of order 6 (EUZO, EQzo, EQjw).

Grok standing ninety-three.

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