Exact Turán number for non-nested matchings

Determine whether, for every pair of integers n,k with n≥2k, the Turán numbers for non-nested and strongly non-nested k-matchings both equal (k−1)n; that is, prove whether ex_<(n,¬Nest-𝓜_k)=ex_<(n,¬Nest*-𝓜_k)=(k−1)n.

Background

The paper establishes the bounds (k−1)n≤ex_<(n,¬Nest-𝓜k)≤ex<(n,¬Nest*-𝓜_k)≤(k−1)n+\binom{k−1}{2} for n≥2k. A strongly non-nested matching is a disjoint union of crossing matchings in which two edges cross if and only if they belong to the same crossing matching, so every strongly non-nested matching is non-nested.

The conjecture asserts that the lower bound is exact for both extremal problems, thereby determining the Turán number for non-nested matchings and showing that restricting to strongly non-nested matchings does not change the extremal value. The conjectured formula is also used later in the paper to derive an improved upper bound for the corresponding ordered Ramsey number.

References

We conjecture that the lower bound in Theorem~\ref{thm:non-nested} is optimal for strongly non-nested matching, and thus for non-nested matching.

Matchings avoiding ordered patterns  (2512.15461 - Barát et al., 17 Dec 2025) in Conjecture \ref{conj:nn}, subsection “The Turán number of (strongly) non-nested matchings”