Tokushige's conjecture on non-uniform cross-t-intersecting families

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Let k≥l≥t≥1k\geq l\geq t\geq1 and n≥(t+1)(k−t+1)n\geq(t+1)(k-t+1). Two families A⊆([n]k)\mathcal{A}\subseteq\binom{[n]}{k} and B⊆([n]l)\mathcal{B}\subseteq\binom{[n]}{l} are cross-tt-intersecting if ∣A∩B∣≥t|A\cap B|\geq t for every A∈AA\in\mathcal{A} and B∈BB\in\mathcal{B}. Tokushige's conjecture. Then

∣A∣∣B∣≤(n−tk−t)(n−tl−t).|\mathcal{A}||\mathcal{B}|\leq\binom{n-t}{k-t}\binom{n-t}{l-t}.

This is presented as a conjecture for non-uniform cross-tt-intersecting families, and the supplied text gives no resolution status.

References

Primary source

Jingjun Bao and Lijun Ji, “The maximum product of sizes of cross-\(t\)-intersecting families”, arXiv:2510.11724 (2025).

Additional references

2 papers in this index state this conjecture (2025). The statement above is taken from the most recent of them; the others are arXiv:2510.26642.

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