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arXiv · 2606.00653

Combinatorial interpretations of Tutte polynomials at the point $(2,-1)$

Yu Chen·Xian'an Jin·Tianlong Ma
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Abstract

Let $G$ be a simple connected graph, and let $T_{G}(x,y)$ be the Tutte polynomial of $G$. Motivated by the works in \cite{Ma}, we, in this paper, introduce the even-left spanning forests of $G$ and odd $G$-partitionable permutations, and show that $T_{G}(2,-1)$ is equal to both the number of even-left spanning forests of $G$ and the number of odd $G$-partitionable permutations. In particular, for a complete graph $K_n$, we prove that $T_{K_{n}}(2,-1)$ is the number of alternating permutations on $\{1,2,\dots,n+1\}$, using two distinct techniques: a recurrence relation and an explicit bijection construction.

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Yu Chen, Xian'an Jin, Tianlong Ma. 2026-05-30. Combinatorial interpretations of Tutte polynomials at the point $(2,-1)$. https://arxiv.org/abs/2606.00653

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