Exact Fourier certificates for complex Hadamard matrices of order six

OpenAI

For every order-six complex Hadamard matrix outside Tao’s cubic equivalence class, the normalized character sum vanishes at every permutation of (1,1,1,−1,−1,−1), allowing row and column permutations and arbitrary unit phases.

Sources for this record

What was already known

Matolcsi, Ruzsa and Weiner conjectured this vanishing; Maxwell and Brierley proved it for the Karlsson family. The arbitrary-phase case outside Tao’s class remained.

AI involvement AI-led

OpenAI is the named author of the model-produced manuscript. The available release does not name a human checker or human explanation of its certificate argument.

The September 24 paper credits OpenAI as author, and the release identifies the manuscript collection as model-produced.

Importance Notable

Extends a family result to the full non-Tao order-six class.

Limitations

The selected Lean clause and exact integer/rational certificates address this Fourier statement. They do not establish the stronger N(6)=3 mutually unbiased bases claim.

Technical verification Formal (Lean 4 and exact integer/rational Python certificate verification)

The paper specifies exact integer and rational moment certificates and provides a complete standard-library verifier. A proof-bearing Lean endpoint states the same Hadamard vanishing result outside Tao equivalence. The selected Lean statement also has a weaker at-most-five MUB clause; it must not be read as a proof of N(6)=3. The source reports these machine checks, but this review did not run them.

Formal checking

Proof-bearing Lean declaration with a separate comparator statement

Checker
Lean 4 in the OpenAI formalization release
Scope
The Fourier-vanishing clause of OAI.MUB6.fourier_and_family_bound for every non-Tao-equivalent order-six Hadamard matrix
Basis
Reported by the linked checker
Evidence source

Formal checking

Exact integer/rational certificate verification with a checksum wrapper

Checker
The manuscript's standard-library Python verifier
Scope
Finite invariant-moment identities used for the single-matrix Fourier dichotomy
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 paper explains the moment-certificate and cubic-class dichotomy, but no human-authored explanation of that mechanism is identified. Few is the evidence default.

Correction and publication history