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An extremal theorem for non-isomorphic spanning trees
Abstract
For a graph G, let τiso(G) denote the number of isomorphism classes of its spanning trees. For every fixed d≥3 and all sufficiently large n, we prove that every connected n-vertex graph G with δ(G)≥ d satisfies τiso(G)≥ τiso(Kd,n−d)=Adnd−1+Od(nd−2), for an explicit constant Ad>0, and Kd,n−d is the unique minimizer. This confirms a conjecture of Bitonti, Michel and Scott and extends it to every d≥3. We also show that any such graph with O(nd−1) spanning-tree types has all but a bounded number of vertices with the same d neighbours.
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BibTeX
@misc{yan2026extremal,
title = {{An extremal theorem for non-isomorphic spanning trees}},
author = {Zhifei Yan and Lu-Ming Zhang},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.30201},
eprint = {2609.30201},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.30201},
}
RIS
TY - UNPB
TI - An extremal theorem for non-isomorphic spanning trees
AU - Zhifei Yan
AU - Lu-Ming Zhang
PY - 2026
DA - 2026/09/24
PB - arXiv
DO - 10.48550/arxiv.2609.30201
UR - https://arxiv.org/abs/2609.30201
AB - For a graph G, let τ_iso(G) denote the number of isomorphism classes of its spanning trees. For every fixed d≥3 and all sufficiently large n, we prove that every connected n-vertex graph G with δ(G)≥ d satisfies τ_iso(G)≥ τ_iso(K_d,n−d)=A_dn^d−1+O_d(n^d−2), for an explicit constant A_d>0, and K_d,n−d is the unique minimizer. This confirms a conjecture of Bitonti, Michel and Scott and extends it to every d≥3. We also show that any such graph with O(n^d−1) spanning-tree types has all but a bounded number of vertices with the same d neighbours.
ER -