Mészáros–Rónyai conjecture on deleting a member of an s-extremal family

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For a family F⊆2[n]\mathcal{F}\subseteq 2^{[n]}, let tr⁡(F)\operatorname{tr}(\mathcal{F}) be its trace family. The family is s-extremal when

∣tr⁡(F)∣=∣F∣.|\operatorname{tr}(\mathcal{F})|=|\mathcal{F}|.

Mészáros–Rónyai conjecture. For every nonempty s-extremal family F⊆2[n]\mathcal{F}\subseteq 2^{[n]}, there exists F0∈FF_0\in\mathcal{F} such that F∖{F0}\mathcal{F}\setminus\{F_0\} is still s-extremal.

The conjecture is known for hereditary families and for all families with VC dimension at most 22; it remains open in general.

References

Primary source

Mingze Li, Jie Ma and Mingyuan Rong, “Recent advances in arrow relations and traces of sets”, arXiv:2507.23375 (2025).

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