Kalai–Meagher conjecture on intersecting families of triangulations

Let d4f4nd4f4_n denote the set of triangulations of a convex nn-gon, and let d4f4n1d4f4_{n-1} denote the corresponding set for a convex (n1)(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 n3n\geq 3,

α(KG(Tn))=Tn1=Cn3,\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 (n1)(n-1)-gon. The statement is presented as an open problem in the paper, and no resolution is supplied.

Sources & referencesView supporting material

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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