Universal lower bound conjecture for binary search tree height of permuton samples

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Let cmathcalPμncmathcal{P}^n_\mu be a sample of nn points from a permuton cmucmu, and let cmathcalT⟨Pμn⟩cmathcal{T}\langle\mathcal{P}^n_\mu\rangle be the corresponding binary search tree, with height denoted by h(T⟨Pμn⟩)h(\mathcal{T}\langle\mathcal{P}^n_\mu\rangle). Let c∗c^* be the unique solution with c≥2c\geq 2 of

clog⁡(2e/c)=1.c\log(2e/c)=1.

Universal height lower-bound conjecture. For any permuton cmucmu and cvarepsilon>0cvarepsilon>0,

lim⁡n→∞P[h(T⟨Pμn⟩)log⁡n<c∗−ε]=0.\lim_{n\to\infty}\mathbb{P}\left[\frac{h\left(\mathcal{T}\langle\mathcal{P}^n_\mu\rangle\right)}{\log n}<c^*-\varepsilon\right]=0.

The conjecture asserts that the uniform-permuton constant c∗c^* is a universal lower bound for the typical logarithmic height of binary search trees built from permuton samples, even when the hypotheses of the proved universality theorem fail. The paper notes that no permuton with asymptotically smaller height and non-vanishing probability is known, while examples show that the height can be larger than c∗log⁡nc^*\log n.

References

Primary source

Benoît Corsini, Victor Dubach and Valentin Féray, “Binary search trees of permuton samples”, arXiv:2403.03151 (2025).

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