The fixed-edge extremal conjecture for t-intersecting trees

From papers

Let KnK_n be the complete graph on nn vertices, and let a family of spanning trees of KnK_n be tt-intersecting if any two trees in the family have at least tt edges in common. For a fixed set EE of tt pairwise disjoint edges, write

Tn(E)={T:T is a spanning tree of Kn and ET}.\mathcal{T}_n(E)=\{T:T\text{ is a spanning tree of }K_n\text{ and }E\subseteq T\}.

Fixed-edge extremal conjecture. If tn/2t\le n/2, then the largest tt-intersecting family of spanning trees is

Tn(E)\mathcal{T}_n(E)

for some fixed set EE of tt disjoint edges.

This is a complete extremal prediction for the range tn/2t\le n/2. The paper presents it as an open problem, while later results may clarify its relation to the broader conjecture about trivial families.

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Primary source

Peter Frankl, Glenn Hurlbert, Ferdinand Ihringer, Andrey Kupavskii, Nathan Lindzey, Karen Meagher and Venkata Raghu Tej Pantangi, “Intersecting Families of Spanning Trees”, arXiv:2502.08128 (2025).

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