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We develop basic cluster theory from an elementary point of view using a variation of binary trees which we call mixed cobinary trees. We show that the number of isomorphism classes of such trees is given by the Catalan number Cn where n is…

Combinatorics · Mathematics 2013-08-12 Kiyoshi Igusa , Jonah Ostroff

Maximal green sequences are particular sequences of quiver mutations appearing in the context of quantum dilogarithm identities and supersymmetric gauge theory. Interpreting maximal green sequences as paths in various natural posets arising…

Representation Theory · Mathematics 2013-03-01 Thomas Brüstle , Grégoire Dupont , Matthieu Pérotin

We study what we call the Hom-Ext quiver and characterize it as a type of `superquiver'. In type $\tilde{\mathbb{A}}$, the Hom-Ext quiver of an exceptional set is the tiling algebra of the corresponding geometric model. And, in that case,…

Representation Theory · Mathematics 2026-03-23 Kiyoshi Igusa , Ray Maresca

A congruence of the weak order is simple if its quotientope is a simple polytope. We provide an alternative elementary proof of the characterization of the simple congruences in terms of forbidden up and down arcs. For this, we provide a…

Combinatorics · Mathematics 2026-05-07 Emily Barnard , Jean-Christophe Novelli , Vincent Pilaud

We look at a family of meta-Fibonacci sequences which arise in studying the number of leaves at the largest level in certain infinite sequences of binary trees, restricted compositions of an integer, and binary compact codes. For this…

Combinatorics · Mathematics 2007-05-23 Brad Jackson , Frank Ruskey

Noncrossing partition posets in a Coxeter group $W$ can fail to be lattices when $W$ is not finite. When the lattice property fails for $W$ of affine type, McCammond and Sulway's construction provides a larger lattice that contains the…

Representation Theory · Mathematics 2025-10-21 Eric J. Hanson , Nathan Reading

We investigate maximal exceptional sequences of line bundles on (P^1)^3, i.e. those consisting of 2^r elements. For r=3 we show that they are always full, meaning that they generate the derived category. Everything is done in the discrete…

Algebraic Geometry · Mathematics 2022-01-03 Klaus Altmann , Martin Altmann

We produce full strong exceptional collections consisting of vector bundles on the geometric invariant theory quotient of certain linear actions of a split reductive group $G$ of rank two. The vector bundles correspond to irreducible…

Algebraic Geometry · Mathematics 2025-10-28 Daniel Halpern-Leistner , Kimoi Kemboi

We introduce the notions of $\tau$-exceptional and signed $\tau$-exceptional sequences for any finite dimensional algebra. We prove that for a fixed algebra of rank $n$, and for any positive integer $t \leq n$, there is a bijection between…

Representation Theory · Mathematics 2021-06-04 Aslak Bakke Buan , Bethany Marsh

Noncrossing arc diagrams are combinatorial models for permutations that encode information about lattice congruences of the weak order and about the associated discrete geometry. In this paper, we consider two related, analogous models for…

Combinatorics · Mathematics 2025-04-22 Emily Barnard , Nathan Reading , Ashley M. Tharp

The notion of a $\tau$-exceptional sequence was introduced by Buan and Marsh in 2018 as a generalisation of an exceptional sequence for finite dimensional algebras. We calculate the number of complete $\tau$-exceptional sequences over…

Representation Theory · Mathematics 2021-06-18 Dixy Msapato

We examine the behavior of the sequences of $p$-adic valuations of quadratic polynomials with integer coefficients for an odd prime $p$ through tree representations. Under this representation, a finite tree corresponds to a periodic…

Number Theory · Mathematics 2023-09-29 Will Boultinghouse , Emily Hammett , Stephen Hu , Olena Kozhushkina , Rachel Snyder , Justin Trulen

It is well-known that a quiver Q of type A_n is representation-finite, and that its indecomposable representations are thin (all Jordan-Hoelder multiplicities are 0 or 1). By now, various methods of proof are known. The aim of this note is…

Representation Theory · Mathematics 2013-04-23 Claus Michael Ringel

The paper proposes a new variant of a decision tree, called an Extreme Learning Tree. It consists of an extremely random tree with non-linear data transformation, and a linear observer that provides predictions based on the leaf index where…

Machine Learning · Computer Science 2019-12-20 Anton Akusok , Emil Eirola , Kaj-Mikael Björk , Amaury Lendasse

We investigate quiver representations over $\mathbb{F}_1$. Coefficient quivers are combinatorial gadgets equivalent to $\mathbb{F}_1$-representations of quivers. We focus on the case when the quiver $Q$ is a pseudotree. For such quivers, we…

Representation Theory · Mathematics 2023-01-19 Jaiung Jun , Jaehoon Kim , Alex Sistko

We classify spherical modules and full exceptional sequences of modules over the Auslander algebra of $k[x]/(x^t)$. We categorify the left and right symmetric group actions on these exceptional sequences to two braid group actions: of…

Representation Theory · Mathematics 2019-11-27 Lutz Hille , David Ploog

This work is the sequel to Continuous Quivers of Type A (I). In this paper we define the Auslander-Reiten space of a continuous type $A$ quiver, which generalizes the Auslander-Reiten quiver of type $A_n$ quivers. We prove that extensions,…

Representation Theory · Mathematics 2020-01-17 Job Rock

We study linear series on a general curve of genus g, whose images are exceptional with respect to their secant planes. Each such exceptional secant plane is algebraically encoded by an included linear series, whose number of base points…

Algebraic Geometry · Mathematics 2020-06-30 Ethan Cotterill , Xiang He , Naizhen Zhang

We show that ''almost all'' exceptional modules over wild canonical algebra $\Lambda$ can be described by matrices having coefficients $\lambda_i-\lambda_j$, where $\lambda_i, \lambda_j$ are elements from the parameter sequence. The proof…

Rings and Algebras · Mathematics 2019-03-26 Dawid Edmund Kędzierski , Hagen Meltzer

We provide a classification of generalized tilting modules and full exceptional sequences for the dual extension algebra of the path algebra of a uniformly oriented linear quiver modulo the ideal generated by paths of length two with its…

Representation Theory · Mathematics 2022-04-01 Elin Persson Westin , Markus Thuresson