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Peer-reviewedCC BY 4.0The Electronic Journal of Combinatorics

Unexpectedly, a Symmetry on Unlabeled Graphs

Abstract

We exhibit the joint symmetric distribution of the following two parameters on the set of unlabeled simple connected graphs with n vertices. The first parameter is the maximal number of leaves attached to a vertex. The second parameter is the size of the largest set of vertices sharing the same closed neighborhood minus $1$. Apparently, this is the first example of a natural non-trivial equidistribution of graph parameters on unlabeled simple connected graphs with a fixed set of vertices. Our proof is enumerative, using the theory of species. Exhibiting an explicit bijection interchanging the two parameters remains an open problem.

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BibTeX
@article{furnsinn2026unexpectedly,
  title = {{Unexpectedly, a Symmetry on Unlabeled Graphs}},
  author = {Florian Fürnsinn and Moritz Gangl and Martin Rubey},
  journal = {The Electronic Journal of Combinatorics},
  year = {2026},
  month = nov,
  doi = {10.37236/15312},
  url = {https://www.combinatorics.org/ojs/index.php/eljc/article/view/v33i4p32},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Unexpectedly, a Symmetry on Unlabeled Graphs
AU  - Florian Fürnsinn
AU  - Moritz Gangl
AU  - Martin Rubey
PY  - 2026
DA  - 2026/11/06
JO  - The Electronic Journal of Combinatorics
DO  - 10.37236/15312
UR  - https://www.combinatorics.org/ojs/index.php/eljc/article/view/v33i4p32
AB  - We exhibit the joint symmetric distribution of the following two parameters on the set of unlabeled simple connected graphs with n vertices. The first parameter is the maximal number of leaves attached to a vertex. The second parameter is the size of the largest set of vertices sharing the same closed neighborhood minus $1$. Apparently, this is the first example of a natural non-trivial equidistribution of graph parameters on unlabeled simple connected graphs with a fixed set of vertices. Our proof is enumerative, using the theory of species. Exhibiting an explicit bijection interchanging the two parameters remains an open problem.
SN  - 1077-8926
ER  -