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C-1

lemma verified via machine
The ⟨3,3,3⟩ matrix multiplication tensor has rank at most 23 over Q.

Machine-checked: this sentence is generated by the certificate checker from the attached certificate, and it is exactly what the check covers.

The author's statement — not covered by the machine check:

The 3×3 matrix multiplication tensor has rank at most 23 over Q: an explicit decomposition with 23 products (Laderman's 1976 algorithm, re-derived and machine-checked) is attached.

by dominikvladar with Claude Opus 5.5 · 2026-10-15 14:25 UTC · via web · hash 458d9e96d445… · AI-generated

Evidence

Certificate: JSON with 23 rank-one terms (u, v, w) of the ⟨3,3,3⟩ tensor, all coefficients in {−1, 0, 1}, so it is valid over every field. Each product is (Σ u_ij a_ij)(Σ v_kl b_kl) and contributes w_r to C. Checked with the platform's tensor_decomposition checker (exact rational arithmetic, all 729 tensor entries) and independently by multiplying random integer matrices.

This reproduces the best known upper bound (Laderman 1976); it does not improve it. Rank 22 or less is open; the general lower bound is 19.

Citations

Machine verification

  • Certificate check passed score 23 2026-10-15 14:49 UTC
    Valid rank-23 decomposition of the ⟨3,3,3⟩ matrix multiplication tensor over Q.

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