A counterexample to Ryser's covering conjecture

OpenAI

For every sufficiently large prime s≡2 mod 3 and sufficiently large odd n depending on s, the September 23 manuscript constructs an intersecting (s^n+1)-partite uniform hypergraph with matching number one and covering number s^n+1, exceeding Ryser’s proposed bound s^n.

Sources for this record

What was already known

Ryser’s inequality was proved in several low ranks. A separate published OpenAI result gives balanced counterexamples at every sufficiently large prime order using a later construction.

AI involvement AI-led

OpenAI credits its internal model with the original odd-extension construction. No named human proof check or explanation of it is documented.

The OpenAI-authored manuscript and release document central internal-model work, while the exact independence of this run is not established.

Importance Major

This earlier odd-extension family supplies a distinct, formally checked route to violating the covering inequality.

Limitations

The theorem uses existential large-prime and odd-degree thresholds; it does not assert balanced parts or a small-rank example. Its companion graph corollary addresses a separate covering conjecture.

Technical verification Formal (Lean 4 with Mathlib and Comparator target)

The Lean eventual-odd theorem constructs finite intersecting r-partite hypergraphs with matching number one and cover number r for every sufficiently large eligible prime and odd extension degree. It does not assert balanced parts or explicit thresholds.

Formal checking

Lean proof of eventual odd-extension hypergraph counterexamples

Checker
Lean 4 kernel, as reported by the OpenAI math release
Scope
Eventual odd-extension finite hypergraphs that violate Ryser's covering inequality
Basis
Reported by the linked checker
Evidence source

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

Human understanding Few

No named human explanation of the finite-plane modification, incidence argument or exceptional-edge construction is documented. Few is the evidence default.

Correction and publication history

2026-10-18 · publication

This earlier odd-extension family supplies a distinct, formally checked route to violating the covering inequality.

Read this published revision