Open Research Index

On the local geometry of the tight 39-point code in 𝕆P²

Robert R. MacGregor

Palomar Registrypalomar/PALOMAR-2026-10-29-000034Oct 29, 2026math.DGscore 0

Cohn, Kumar and Minton constructed a universally optimal code of thirty-nine points in the octonionic projective plane 𝕆P², whose existence was conjectured by Hoggar. Its points form thirteen mutually unbiased Jordan frames, and a four-parameter phase family deforms the code through such configurations. This Lean development describes their local geometry under the automorphism group F₄. At every nonresonant phase, every nearby real solution of the defining equations belongs to one of four smooth families of labelled configurations. In a local slice for F₄, their union has normal form R⁴ ×…

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