Butterfly supersaturation conjecture up to the packing number

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Let [n]={1,…,n}[n]=\{1,\ldots,n\}, let 2[n]2^{[n]} denote the family of all subsets of [n][n], and let Σ(n,2)\Sigma(n,2) be the size of the two middle levels of the Boolean lattice. Write K(n,⌈n/2⌉+1)K(n,\lceil n/2\rceil+1) for the largest family of (⌈n/2⌉+1)(\lceil n/2\rceil+1)-element sets whose distinct members have intersection at most ⌈n/2⌉−1\lceil n/2\rceil-1, and let f(n)f(n) denote the number of butterflies containing one additional set above the two middle levels.

Butterfly supersaturation conjecture. Let E=E(n)≤K(n,⌈n/2⌉+1)E=E(n)\le K(n,\lceil n/2\rceil+1). If nn is large enough, then the minimum number of butterflies a family F⊂2[n]\mathcal F\subset 2^{[n]} of size Σ(n,2)+E\Sigma(n,2)+E must contain is Ef(n)Ef(n).

The claim predicts the exact supersaturation threshold for families just larger than the two middle levels, within the range allowed by the packing parameter K(n,⌈n/2⌉+1)K(n,\lceil n/2\rceil+1). The paper explains that its methods do not reach this range even asymptotically, so the conjecture remains open.

References

Primary source

Balazs Patkos, “Supersaturation and stability for forbidden subposet problems”, arXiv:1406.1887 (2015).

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