OpenAI reports an Eilenberg–Ganea counterexample

There is a finitely generated residually finite group of integral cohomological dimension two and geometric dimension three.

Sources for this record

What was already known

Cohomological and geometric dimensions were known to agree above dimension two and in dimension one. The remaining Eilenberg–Ganea conjecture predicted agreement at cohomological dimension two.

AI involvement AI-led

OpenAI credits itself as manuscript author and states that its internal frontier model produced the results in this release. Individual human input is not detailed enough to establish task-only autonomy.

OpenAI is named as author on the manuscript, and its release attributes the results to an internal frontier model. The individual human input is not detailed enough to establish autonomy.

Importance Major

Disproves the long-standing Eilenberg–Ganea conjecture with a finitely generated residually finite example.

Limitations

The claim concerns ordinary integral cohomological dimension and classifying-space dimension.

Technical verification Formal (Lean 4)

OpenAI reports a Lean proof matching the selected claim.

Formal checking

The pinned Lean note constructs a finitely generated residually finite group with cohomological dimension two and geometric dimension three.

Checker
OpenAI-reported Lean 4 / Comparator
Scope
There is a finitely generated residually finite group of integral cohomological dimension two and geometric dimension three.
Basis
Reported by the linked checker
Evidence source

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

Human understanding Few

Few is the default when evidence for a higher level is insufficient. No named person is documented as explaining the central argument for this assessed contribution.

Correction and publication history

2026-10-18 · publication

Primary manuscript, attribution, prior-work, and scoped checking review for non-notifying local inclusion.

Read this published revision