# Verification report

The five-page manuscript proves a necessary-and-sufficient extremality
criterion for jointly square-zero contraction tuples, tested against all
commuting contractive extensions. It also proves finite-dimension bounds,
an explicit minimal odd-dimensional example in that class, its amplifications,
and a quantitative extension-column estimate under a bounded-below assumption.
The unrestricted OWR-3470-005 classification is not solved.

The proof audit in reproducibility/proof_audit.md checks the arbitrary
extension blocks, the contractive rank-one witnesses, the complex scalar
obstruction, and the precise domain of the dimension claims. The proof
requires no outside approval gate but does not claim independent review.

The exact standard-library checker verifies all coisometry identities and
zero products for the displayed tuple. Its 12 by 12 kernel matrix has rank
12 and determinant -8, computed independently by Gaussian elimination and
a subset-permutation recurrence. The first three tensor amplifications have
ranks 12, 24 and 36. All 24 signed coordinate fourth blocks are checked;
their ranks are 9, 11 and 12 with multiplicities 6, 6 and 12. Twenty-six
kernel-witness extensions, a separate defect extension, a known unitary
case and the shift negative control pass exact checks. No floating-point
comparison is used. Run the checker without -O; assertions are mandatory.

These computations support finite instances; the written block argument is
the proof for arbitrary dimensions. No proof-assistant certification is
claimed. Timko's unitary criterion and block method are explicitly credited.
The targeted primary-source comparison does not establish absolute novelty.

The package build record separately records compilation, visual inspection,
clean source-archive rebuild and checker replay. A local ready package is
not a published deposit. No DOI, website deployment, HF announcement or
arXiv submission is asserted by this report.