Super Hayashi Quandles

Antonio Lages; Pedro Lopes

Home/Archive/arXiv

arXiv · 2405.12329

Super Hayashi Quandles

Antonio Lages·Pedro Lopes

View original source ↗Read source document ↗Export metadata ↓

Abstract

Quandles are right-invertible, right-self distributive (and idempotent) algebraic structures. Therefore, right translations are quandle automorphisms. It has been interesting to look into finite quandles by way of the cycle structures their right translations may have. For each quandle, the list of these cycle structures is known as the profile of the quandle. For a connected quandle, any two right translations are conjugate so there is essentially one cycle structure per connected quandle - which we thus identify with the profile. Hayashi conjectured that, for a connected quandle, each length of its profile divides the longest length. In the present article we introduce Super Hayashi Quandles (SHQ). An SHQ is a finite connected quandle such that any two lengths in its profile are (i) distinct, and (ii) the shorter one divides the longer one. The SHQ's are latin quandles and we prove that their profiles depend only on the second shortest length and on the number of cycles. Furthermore, we prove that SHQ's have SHQ's alone for subquandles (with the same second shortest length but fewer cycles). Finally, we construct infinitely many SHQ's.

Explore related subjects

math.CO

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Antonio Lages, Pedro Lopes. 2026-05-06. Super Hayashi Quandles. https://arxiv.org/abs/2405.12329

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

On Perfect Divisibility of Bull-Free Graphs Without Long Paths

A graph $G$ is {\em perfectly divisible} if, for every induced subgraph $H$ of $G$, $V(H)$ can be partitioned into $A$ and $B$ such that $H[A]$ is perfect and $ω(H[B])<ω(H)$. Chudnovsky and Sivaraman [J. Graph Theory \textbf{90} (2019) 54-60] proved that every ($P_5$, bull)-free graph is perfectly divisible, while Chen and Xu [Discrete Appl. Math. \textbf{372} (2025) 298-307] proved the same for ($P_7,C_5$, bull)-free graphs. We extend these results by proving that every ($P_8,C_5$, bull)-free graph is perfectly divisible and that, letting $F$ denote the Grötzsch graph, a ($P_6$, bull)-free graph is perfectly divisible if and only if it is $F$-free.

math.CO↗

arXiv2026

Covering graphs by isometric trees

A connected subgraph of a graph is isometric if it preserves distances. Recently, graphs admitting a vertex or edge covering by a small number of isometric paths have been studied. In this paper, we consider the analogous problem for isometric trees, focusing on the treewidth of graphs admitting a vertex or edge covering by a small number of such trees. Baste, De Meyer, Giocanti, Objois, and Picavet showed that for coverings by two isometric trees, the treewidth is bounded. We show that already for three isometric trees, the treewidth can be linear in the number of vertices. On the positive side, we show that for graphs of bounded degree coverable by a small number of isometric trees, the treewidth is sublinear in the number of vertices.

math.CO↗

arXiv2026

Tree-independence number of $P_5$-free graphs with no large bicliques

The tree-independence number of a graph is the minimum, over all tree-decompositions of the graph, of the maximum size of an independent set contained in a bag. Graph classes of bounded tree-independence number have strong structural and algorithmic properties; however, the parameter can be unbounded even in quite restricted classes. In particular, the presence of an induced biclique $K_{\ell,\ell}$ forces tree-independence number at least $\ell$. This leads to the question whether large induced bicliques are the only obstruction to bounded tree-independence number in natural hereditary classes. A conjecture of Dallard, Krnc, Kwon, Milanič, Munaro, Štorgel, and Wiederrecht states that for all positive integers $t$ and $\ell$, ${\{P_t,K_{\ell,\ell}\}}$-free graphs have bounded tree-independence number. We prove this conjecture for ${t=5}$ by showing that every ${\{P_5,K_{\ell,\ell}\}}$-free graph has tree-independence number at most ${4\ell-4}$. We also obtain related bounds for the weaker parameter of $α$-degeneracy and answer a question of Hilaire, Milanič, and Vasić whether tree-independence number of ${\{P_5,K_{\ell,\ell}\}}$-free graphs exceeds $\ell$ by at most an additive constant.

math.CO↗