A Counterexample to the Group-Ring Determinant Conjecture

OpenAI

A finitely generated group G and matrix A over Z[G] are constructed with A invertible over Q[G] and Fuglede–Kadison determinant strictly between zero and one. This contradicts the unrestricted group-ring Determinant Conjecture.

Sources for this record

What was already known

The conjecture extends the lower bound of one for nonsingular integer-matrix determinants to integral group-ring matrices. A related direct-finiteness defect alone does not give this determinant witness.

AI involvement AI-led

OpenAI credits an internal model with the determinant manuscript and Lean development, building on its companion direct-finiteness construction.

The release attributes the manuscript and formal proof to an internal model, while the exact level of human steering is unspecified.

Importance Major

The witness overturns a broad group-ring determinant conjecture.

Limitations

The reported Lean proof covers the invertible-operator determinant inequality. The paper’s additional finite negative spectral-log integral is outside that formal statement.

Technical verification Formal (Lean 4 with Mathlib and Comparator)

The reported Lean theorem constructs the integral matrix, its rational inverse and a bounded regular operator with determinant in (0,1), matching the decisive counterexample. The additional spectral-measure integral identity in the paper is outside the formal statement.

Formal checking

Proof of OAI.GroupRingDeterminant.main against GroupRingDeterminant Comparator MainStatement

Checker
Lean 4 kernel, as reported by the OpenAI math release
Scope
A finitely generated group and integral group-ring matrix with rational inverse and Fuglede–Kadison determinant strictly between zero and one
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 determinant transfer and witness is documented; Few is the evidence default.

Correction and publication history