Frankl-complete sunflowers and extremal families of four-sets

Mingchang Liu

Liu’s first release gives FC(4,9)=16 and a co-developed 3:1 core-petal charging argument yielding the nine-petal threshold and FC(4,n)=Θ(n²). A later version extends the asymptotic to FC(k,n)=Θₖ(n^(k−2)) for each fixed k≥2; that general proof is separate from the model-attributed first-release work.

Sources for this record

What was already known

Morris proposed the asymptotic for each fixed k and supplied the lower-bound direction. The four-set asymptotic, local threshold and finite FC(4,9) value remained unresolved in the cited account.

AI involvement AI-centered

Models mainly developed the FC(4,9) classification and jointly developed the charging inequality and core-petal weights with Mingchang Liu. Liu set and refined the problem and supplied the later all-k extension.

The manuscript attribution assigns the finite classification mainly to models and the central four-set charging method to joint human/model work. The all-k extension is kept separately human-credited.

Importance Notable

Resolves the four-uniform case and supplies an exact finite classification.

Limitations

Published exact certificates and exhaustive code check FC(4,9)=16. No completed check of the full four-set asymptotic proof is documented; the later all-k argument is outside the finite certificate’s scope.

Technical verification Partial

The V1 source reports exact certificates and exhaustive computation for FC(4,9)=16. That machine check is confined to the finite classification; no completed rigorous review of the general nine-petal or asymptotic argument is documented, and V2's all-k extension is outside the V1 certificate scope.

Independent checking

Exact finite certificates and exhaustive search cover FC(4,9)=16.

Checker
Liu's published V1 verification program and finite certificates
Scope
Finite FC(4,9)=16 classification, including the fifteen-block negative certificate and exhaustive upper bound
Basis
Reported by the linked checker
Evidence source

Human understanding Full

Liu's account identifies the 3:1 core-petal weights, charging inequality and extremal forcing as the four-set mechanism and credits his proof development; no central part is reported unexplained.

Correction and publication history