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Species trees represent the historical divergences of populations or species, while gene trees trace the ancestry of individual gene copies sampled within those populations. In cases involving rapid speciation, gene trees with topologies…

Populations and Evolution · Quantitative Biology 2015-08-28 James H. Degnan , John A. Rhodes

We give a probabilistic interpretation of the coefficients of the elementary symmetric function expansion of the chromatic quasisymmetric function for any unit interval graph. As a corollary, we prove the Stanley--Stembridge conjecture.

Combinatorics · Mathematics 2025-12-29 Tatsuyuki Hikita

Let $\mathfrak g$ be a Borcherds algebra with the associated graph $G$. We prove that the chromatic symmetric function of $G$ can be recovered from the Weyl denominator identity of $\mathfrak g$ and this gives a Lie theoretic proof of…

Combinatorics · Mathematics 2021-05-21 G. Arunkumar

We study the chromatic symmetric functions of graph classes related to spiders, namely generalized spider graphs (line graphs of spiders), and what we call horseshoe crab graphs. We show that no two generalized spiders have the same…

A semiregular tree is a tree where all non-pendant vertices have the same degree. Belardo et al. (MATCH Commun. Math. Chem. 61(2), pp. 503-515, 2009) have shown that among all semiregular trees with a fixed order and degree, a graph with…

Combinatorics · Mathematics 2009-06-09 Tuerker Biyikoglu , Josef Leydold

The Stanley chromatic symmetric function $X_G$ of a graph $G$ is a symmetric function generalization of the chromatic polynomial, and has interesting combinatorial properties. We apply the ideas of Khovanov homology to construct a homology…

Combinatorics · Mathematics 2015-06-11 Radmila Sazdanovic , Martha Yip

We introduce $H$-chromatic symmetric functions, $X_{G}^{H}$, which use the $H$-coloring of a graph $G$ to define a generalization of Stanley's chromatic symmetric functions. We say two graphs $G_1$ and $G_2$ are $H$-chromatically equivalent…

Combinatorics · Mathematics 2022-05-23 Nancy Mae Eagles , Angèle M. Foley , Alice Huang , Elene Karangozishvili , Annan Yu

As introduced by Gutman and Harary, the independence polynomial of a graph serves as the generating polynomial of its independent sets. In 1987, Alavi, Malde, Schwenk and Erd\H{o}s conjectured that the independence polynomials of all trees…

Combinatorics · Mathematics 2025-01-09 Ethan Y. H. Li , Grace M. X. Li , Arthur L. B. Yang , Zhong-Xue Zhang

In Stanley's seminal 1995 paper on the chromatic symmetric function, he stated that there was no known graph that was not contractible to the claw and whose chromatic symmetric function was not $e$-positive, namely, not a positive linear…

Combinatorics · Mathematics 2020-05-21 Samantha Dahlberg , Angele Foley , Stephanie van Willigenburg

Crew and Spirklt generalize Stanley's chromatic symmetric function to vertex-weighted graphs. One of the primary motivations for extending the chromatic symmetric function to vertex-weighted graphs is the existence of a deletion-contraction…

Combinatorics · Mathematics 2023-08-08 Azzurra Ciliberti

We define the acyclic orientation polynomial of a graph to be the generating function for the sinks of its acyclic orientations. Stanley proved that the number of acyclic orientations is equal to the chromatic polynomial evaluated at $-1$…

Combinatorics · Mathematics 2020-08-25 Byung-Hak Hwang , Woo-Seok Jung , Kang-Ju Lee , Jaeseong Oh , Sang-Hoon Yu

A MacMahon symmetric function is an invariant of the diagonal action of the symmetric group on power series in multiple alphabets of variables. We introduce an analogue of the chromatic symmetric function for vertex-weighted graphs, taking…

Combinatorics · Mathematics 2025-08-04 Jeremy L. Martin , May B. Trist

In this paper we prove that the dominator chromatic number of every oriented tree is invariant under reversal of orientation. In addition to this marquee result, we also prove the exact dominator chromatic number for arborescences and…

Combinatorics · Mathematics 2021-02-01 Michael Cary

A well-known result of Stanley's shows that given a graph $G$ with chromatic symmetric function expanded into the basis of elementary symmetric functions as $X_G = \sum c_{\lambda}e_{\lambda}$, the sum of the coefficients $c_{\lambda}$ for…

Combinatorics · Mathematics 2025-05-16 Logan Crew , Yongxing Zhang

Sazdanovic and Yip defined a categorification of Stanley's chromatic function called the chromatic symmetric homology. In this paper we prove that (as conjectured by Chandler, Sazdanovic, Stella and Yip), if a graph $G$ is non-planar, then…

Combinatorics · Mathematics 2023-07-19 Azzurra Ciliberti , Luca Moci

An edge-colored graph $G$ is called properly colored if every two adjacent edges are assigned different colors. A monochromatic triangle is a cycle of length 3 with all the edges having the same color. Given a tree $T_0$, let…

Combinatorics · Mathematics 2026-04-02 Ruonan Li , Ruhui Lu , Xueli Su , Shenggui Zhang

We study Stanley's chromatic symmetric function (CSF) for trees when expressed in the star basis. We use the deletion-near-contraction (DNC) algorithm to compute coefficients that occur in the CSF in the star basis. In particular, one of…

Combinatorics · Mathematics 2025-07-23 Michael Gonzalez , Rosa Orellana , Mario Tomba

We study the chromatic symmetric function on graphs, and show that its kernel is spanned by the modular relations. We generalize this result to the chromatic quasisymmetric function on hypergraphic polytopes, a family of generalized…

Combinatorics · Mathematics 2020-03-31 Raul Penaguiao

We study a notion of potential isomorphism, where two structures are said to be potentially isomorphic if they are isomorphic in some generic extension that preserves stationary sets and does not add new sets of cardinality less than the…

Logic · Mathematics 2007-05-23 Alex Hellsten , Tapani Hyttinen , Saharon Shelah

There is an unproven duality theory hypothesizing that random discrete trees and their poissonized embeddings in continuous time share fundamental properties. We give additional evidence in favor of this theory by showing that several…

Probability · Mathematics 2019-03-04 Carly Domicolo , Panpan Zhang , Hosam Mahmoud