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arXiv · 2407.06869

Forcing quasirandomness with 4-point permutations

Daniel Kráľ·Jae-baek Lee·Jonathan A. Noel
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Abstract

A combinatorial object is said to be quasirandom if it exhibits certain properties that are typically seen in a truly random object of the same kind. It is known that a permutation is quasirandom if and only if the pattern density of each of the twenty-four 4-point permutations is close to 1/24, which is its expected value in a random permutation. In other words, the set of all twenty-four 4-point permutations is quasirandom-forcing. Moreover, it is known that there exist sets of eight 4-point permutations that are also quasirandom-forcing. Breaking the barrier of linear dependency of perturbation gradients, we show that every quasirandom-forcing set of 4-point permutations must have cardinality at least five.

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Daniel Kráľ, Jae-baek Lee, Jonathan A. Noel. 2024-07-09. Forcing quasirandomness with 4-point permutations. https://arxiv.org/abs/2407.06869

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