Astra finds a five-generator semigroup family with exact Betti count

For k≥3 and q≥k−1, let m=2kq+1. The numerical semigroup minimally generated by m,m+1,m+k,m+2k−1,m+2k has toric-ideal generator count 4k+2. The formal development also gives a nonredundant presentation.

Sources for this record

What was already known

A separate theorem gives a linear bound for four-generated semigroups. Shifted-semigroup work provides a periodicity window, but neither supplies this exact five-generator family.

AI involvement AI-centered

Ben Keene set the project and reviewed correspondence. GPT-6 Astra supplied the family presentation, minimality argument and formal minimality proofs; Claude supplied scaffolding.

Astra supplied the retained informal presentation and minimality argument within Keene’s directed family project; the source does not establish full autonomy.

Importance Modest

Gives an unbounded five-generator family with an exact first Betti count and presentation.

Limitations

The proposed bound β₁≤2w+2 for all five-generated semigroups remains conjectural. Machine checks are reported for the family statements; no external human proof check is documented. The novelty search is incomplete, and the reported multi-system check predates the final documentation revision.

Technical verification Formal (Lean 4 kernel, NanoDa and con-ron through Comparator)

The cited record reports sorry-free Lean proof and successful Comparator checks with Lean, NanoDa and con-ron for all three F statements at the later packaging run. Theorem W lies outside the solution closure with an admitted proof and is not rated as proved. Source-reported; this review did not reproduce kernels.

Independent checking

Comparator statement check and multi-kernel proof replay

Checker
Lean, NanoDa and con-ron on the reported GitHub Actions run 39036226197
Scope
F: family spanRank 4k+2, minimal five-generation and explicit nonredundant presentation
Basis
Reported by the linked checker
Evidence source

Human understanding Few

Default for undocumented human explanation of the complete family proof: Keene read correspondence, while the named mathematical reviews and reconstruction were by Astra.

Correction and publication history

2026-10-18 · publication

Gives an unbounded five-generator family with an exact first Betti count and presentation.

Read this published revision