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Precise statement
A $t$-$(v,k,\lambda)$ covering is a family of $k$-subsets of a $v$-set meeting every $t$-subset at least $\lambda$ times, and $C(v,k,t)$ is the least number of blocks. The recorded bounds for $C(12,6,4)$ were $40 \le C(12,6,4) \le 41$. No $4$-$(12,6,1)$ covering with $40$ blocks exists, so $C(12,6,4) = 41$.
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fidelity, correctness, priority, or novelty.
What AI did
GPT-5.6 Sol, GPT-5.6 Terra, Claude Fable 5
The disclosure lists exploratory analysis, computational search, supporting code, manuscript drafting and revision, and proofreading, without separating which step came from where, so the lowest tier applies.
The non-existence argument is a forced-structure search: a counting argument pins every point to degree exactly 20 and forces each point link to be an optimal 3-(11,5,1) covering, collapsing the search space. Single-author arXiv preprint, not peer-reviewed.