Brill--Noether existence and rank for graphs through genus six

Nathan Pflueger

For every connected finite loopless multigraph of genus g≤6 and integers d,r≥0 with ρ=g−(r+1)(g−d+r)≥0, a degree-d divisor of Baker–Norine rank at least r exists. The new case is genus six, proved by descending special divisors from odd subdivisions to the original graph.

Sources for this record

What was already known

Atanasov and Ranganathan had proved existence through genus five. Earlier tropical and subdivision results did not establish the discrete genus-six statement on the original graph.

AI involvement AI-centered

Nathan Pflueger supplied direction, notes and sources. The project credits agents with devising the decisive odd-subdivision descent and formal proof.

Agents supplied the decisive odd-subdivision descent within Pflueger's human-directed research.

Importance Notable

Extends Baker’s graph Brill–Noether existence conjecture by one genus.

Limitations

The reported Lean proof covers existence through genus six. Separate rank and once-marked results in the project require their own assessments; no completed human check or human explanation of this descent is documented.

Technical verification Formal (Lean 4/Mathlib)

The repository reports a sorry-free Lean proof of the exact genus-six statement with only standard axioms.

Formal checking

Repository reports a sorry-free Lean theorem with standard axioms for the exact genus-six existence statement.

Checker
Lean 4 kernel, as reported by the project
Scope
GenusSix.brill_noether_existence_through_six for finite connected loopless multigraphs
Basis
Reported by the linked checker
Evidence source

Checking a formal statement does not establish that it matches the original problem.

Human understanding Few

The human author checked the statement against published definitions, but a named human explanation of the central descent proof is not documented; Few is the evidence-gap default.

Correction and publication history

2026-10-18 · publication

The genus-six existence proof includes an agent-origin descent argument; separate rank and marked results are outside this claim.

Read this published revision