The exact reconstruction threshold for the three-state symmetric channel

OpenAI

For the three-state symmetric channel Kλ(i,i)=(1+2λ)/3 and Kλ(i,j)=(1−λ)/3 for i≠j, with −1/2≤λ≤1, reconstruction from depth-ℓ spins and the observed tree on every regular b-ary tree (integer b≥2) and observed Poisson(d) tree (d>1) occurs exactly when dλ²>1 (d=b in the regular case). At admissible equality there is nonreconstruction. Poisson advantage averages over the tree without conditioning on survival.

Sources for this record

What was already known

Kesten–Stigum already gives reconstruction above threshold. Sly and Mossel–Sly–Sohn established sharpness, including equality, for sufficiently large regular branching or Poisson mean; some small-degree cases were known.

AI involvement AI-led

OpenAI credits an internal model with producing the manuscript collection and is the named author. Session-level autonomy is not documented.

OpenAI institutional authorship and its release account support central internal-model work. Session-level independence and a named human-origin theorem step are not documented.

Importance Notable

Resolves the all-degree three-state symmetric threshold in both tree families.

Limitations

The negative channel is included down to λ=−1/2. The exact-arithmetic certificates address finite proof inequalities; the linked Lean result covers only named parameter regions and does not establish the full negative-channel theorem. No complete human proof review is documented.

Technical verification Partial

The manuscript provides exact-arithmetic certificate cases for finite inequalities. A related Lean module proves nonreconstruction only for nonnegative or restricted negative parameters, plus supercritical reconstruction. Neither supplies a documented end-to-end check of the full negative-channel, all-degree theorem; the certificate suite was not rerun in this review.

Human understanding Few

No named human explanation of the central all-degree negative-channel argument is documented. Few is the evidence default.

Correction and publication history

2026-10-18 · publication

If correct, resolves the all-degree three-state symmetric threshold in both tree families.

Read this published revision