Kalai–Meagher conjecture on intersecting families of triangulations

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Let d4f4nd4f4_n denote the set of triangulations of a convex nn-gon, and let d4f4n−1d4f4_{n-1} denote the corresponding set for a convex (n−1)(n-1)-gon. The independence number d6fc(KG⁡(d4f4n))d6fc(\operatorname{KG}(d4f4_n)) is the size of the largest family of triangulations in d4f4nd4f4_n such that any two triangulations intersect.

Kalai–Meagher conjecture. For every n≥3n\geq 3,

α(KG⁡(Tn))=∣Tn−1∣=Cn−3,\alpha(\operatorname{KG}(\mathcal{T}_n))=|\mathcal{T}_{n-1}|=C_{n-3},

where

Ck=1k+1(2kk)C_k=\frac{1}{k+1}\binom{2k}{k}

denotes the kkth Catalan number.

The conjecture asserts that the largest intersecting family consists of all triangulations containing a fixed diagonal, such as 1,3{1,3}; these are in bijection with triangulations of a convex (n−1)(n-1)-gon. The statement is presented as an open problem in the paper, and no resolution is supplied.

References

Primary source

Anton Molnar, Cosmin Pohoata, Michael Zheng and Daniel G. Zhu, “A Lovász-Kneser theorem for triangulations”, arXiv:2510.27689 (2025).

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