The fixed-edge extremal conjecture for t-intersecting trees

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

Fixed-edge extremal conjecture. If t≤n/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 t≤n/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.

References

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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