bluuebunny/crossref_metadata_2025_split huggingface dataset:
Edge Reconstruction of the Ihara Zeta Function
Authors: Cornelissen Gunther , Kool Janne 
Published: January 2020

We show that if a graph $G$ has average degree $\overline d \geq 4$, then the Ihara zeta function of $G$ is edge-reconstructible. We prove some general spectral properties of the edge adjacency operator $T$: it is symmetric for an indefinite form and has a "large" semi-simple part (but it can fail to be semi-simple in general). We prove that this implies that if $\overline d>4$, one can reconstruct the number of non-backtracking (closed or not) walks through a given edge, the Perron-Frobenius eigenvector of $T$ (modulo a natural symmetry), as well as the closed walks that pass through a given edge in both directions at least once.
On the Potts Antiferromagnet on Random Graphs
Authors: Coja-Oghlan Amin , Jaafari Nor 
Published: January 2020

Extending a prior result of Contucci et al. [Comm. Math. Phys. 2013], we determine the free energy of the Potts antiferromagnet on the Erdős–Rényi random graph at all temperatures for average degrees $d\le (2k-1)\ln k - 2 - k^{-1/2}$. In particular, we show that for this regime of $d$ there does not occur a phase transition.
Elliptic Rook and File Numbers
Authors: Schlosser Michael J. , Yoo Meesue 
Published: January 2020

Utilizing elliptic weights, we construct an elliptic analogue of rook numbers for Ferrers boards. Our elliptic rook numbers generalize Garsia and Remmel's $q$-rook numbers by two additional independent parameters $a$ and $b$, and a nome $p$. The elliptic rook numbers are shown to satisfy an elliptic extension of a factorization theorem which in the classical case was established by Goldman, Joichi and White and extended to the $q$-case by Garsia and Remmel. We obtain similar results for elliptic analogues of Garsia and Remmel's $q$-file numbers for skyline boards. We also provide an elliptic extension of the $j$-attacking model introduced by Remmel and Wachs. Various applications of our results include elliptic analogues of (generalized) Stirling numbers of the first and second kind, Lah numbers, Abel numbers, and $r$-restricted versions thereof.
Small Feedback Vertex Sets in Planar Digraphs
Authors: Esperet Louis , Lemoine Laetitia , Maffray Frédéric 
Published: January 2020

Let $G$ be a directed planar graph on $n$ vertices, with no directed cycle of length less than $g\ge 4$. We prove that $G$ contains a set $X$ of vertices such that $G-X$ has no directed cycle, and $|X|\le \tfrac{5n-5}9$ if $g=4$, $|X|\le \tfrac{2n-5}4$ if $g=5$, and $|X|\le \tfrac{2n-6}{g}$ if $g\ge 6$. This improves recent results of Golowich and Rolnick.
Modification of Griffiths' Result for Even Integers
Authors: Mazumdar Eshita , Sinha Sneh Bala 
Published: January 2020

For a finite abelian group $G$ with $\exp(G)=n$, the arithmetical invariant $\mathsf s_A(G)$ is defined to be the least integer $k$ such that any sequence $S$ with length $k$ of elements in $G$ has a $A$ weighted zero-sum subsequence of length $n$. When $A=\{1\}$, it is the Erdős-Ginzburg-Ziv constant and is denoted by $\mathsf s (G)$. For certain class of sets $A$, we already have some general bounds for these weighted constants corresponding to the cyclic group $\mathbb{Z}_n$, which was given by Griffiths. For odd integer $n$, Adhikari and Mazumdar generalized the above mentioned results in the sense that they hold for more sets $A$. In the present paper we modify Griffiths' method for even $n$ and obtain general bound for the weighted constants for certain class of weighted sets which include sets that were not covered by Griffiths for $n\equiv 0 \pmod{4}$.
Transitive Avoidance Games
Authors: Johnson J. Robert , Leader Imre , Walters Mark 
Published: January 2020

Positional games are a well-studied class of combinatorial games. In their usual form, two players take turns to play moves in a set ('the board'), and certain subsets are designated as 'winning': the first person to occupy such a set wins the game. For these games, it is well known that (with correct play) the game cannot be a second-player win.In the avoidance (or misère) form, the first person to occupy such a set loses the game. Here it would be natural to expect that the game cannot be a first-player win, at least if the game is transitive, meaning that all points of the board look the same. Our main result is that, contrary to this expectation, there are transitive games that are first-player wins, for all board sizes which are not prime or a power of 2.Further, we show that such games can have additional properties such as stronger transitivity conditions, fast winning times, and 'small' winning sets.
Flow Polynomials as Feynman Amplitudes and their $\alpha$-Representation
Authors: Kuptsov Andrey , Lerner Eduard , Mukhamedjanova Sofya 
Published: January 2020

Let $G$ be a connected graph; denote by $\tau(G)$ the set of its spanning trees. Let $\mathbb F_q$ be a finite field, $s(\alpha,G)=\sum_{T\in\tau(G)} \prod_{e \in E(T)} \alpha_e$, where $\alpha_e\in \mathbb F_q$. Kontsevich conjectured in 1997 that the number of nonzero values of $s(\alpha, G)$ is a polynomial in $q$ for all graphs. This conjecture was disproved by Brosnan and Belkale. In this paper, using the standard technique of the Fourier transformation of Feynman amplitudes, we express the flow polynomial $F_G(q)$ in terms of the "correct" Kontsevich formula. Our formula represents $F_G(q)$ as a linear combination of Legendre symbols of $s(\alpha, H)$ with coefficients $\pm 1/q^{(|V(H)|-1)/2}$, where $H$ is a contracted graph of $G$ depending on $\alpha\in \left(\mathbb F^*_q \right)^{E(G)}$, and $|V(H)|$ is odd.
Rainbow Turán Problems for Paths and Forests of Stars
Authors: Johnston Daniel , Palmer Cory , Sarkar Amites 
Published: January 2020

For a fixed graph $F$, we would like to determine the maximum number of edges in a properly edge-colored graph on $n$ vertices which does not contain a rainbow copy of $F$, that is, a copy of $F$ all of whose edges receive a different color. This maximum, denoted by $ex^*(n,F)$, is the rainbow Turán number of $F$, and its systematic study was initiated by Keevash, Mubayi, Sudakov and Verstraëte [Combinatorics, Probability and Computing 16 (2007)]. We determine $ex^*(n,F)$ exactly when $F$ is a forest of stars, and give bounds on $ex^*(n,F)$ when $F$ is a path with $l$ edges, disproving a conjecture in the aforementioned paper for $l=4$.
On $r$-Uniform Linear Hypergraphs with no Berge-$K_{2,t}$
Authors: Timmons Craig 
Published: January 2020

Let $\mathcal{F}$ be an $r$-uniform hypergraph and $G$ be a multigraph. The hypergraph $\mathcal{F}$ is a Berge-$G$ if there is a bijection $f: E(G) \rightarrow E( \mathcal{F} )$ such that $e \subseteq f(e)$ for each $e \in E(G)$. Given a family of multigraphs $\mathcal{G}$, a hypergraph $\mathcal{H}$ is said to be $\mathcal{G}$-free if for each $G \in \mathcal{G}$, $\mathcal{H}$ does not contain a subhypergraph that is isomorphic to a Berge-$G$. We prove bounds on the maximum number of edges in an $r$-uniform linear hypergraph that is $K_{2,t}$-free. We also determine an asymptotic formula for the maximum number of edges in a linear 3-uniform 3-partite hypergraph that is $\{C_3 , K_{2,3} \}$-free.
On the Structure of the Power Graph and the Enhanced Power Graph of a Group
Authors: Aalipour Ghodratollah , Akbari Saieed , Cameron Peter J. , Nikandish Reza , Shaveisi Farzad 
Published: January 2020

Let $G$ be a group‎. ‎The power graph of $G$ is a graph with the vertex‎ ‎set $G$‎, ‎having an edge between two elements whenever one is a power of the other‎. ‎We characterize nilpotent groups whose power graphs have finite independence number‎. ‎For a bounded exponent group‎, ‎we prove its power graph is a perfect graph and we determine‎ ‎its clique/chromatic number‎. ‎Furthermore‎, ‎it is proved that for every group $G$‎, ‎the clique number of the power graph of $G$ is at most countably infinite‎. ‎We also measure how close the power graph is to the commuting graph by introducing a new graph which lies in between‎. ‎We call this new graph as the enhanced power graph‎. ‎For an arbitrary pair of these three graphs we characterize finite groups for which this pair of graphs are equal‎.
Obstructions to Combinatorial Formulas for Plethysm
Authors: Kahle Thomas , Michałek Mateusz 
Published: January 2020

Motivated by questions of Mulmuley and Stanley we investigate quasi-polynomials arising in formulas for plethysm. We demonstrate, on the examples of $S^3(S^k)$ and $S^k(S^3)$, that these need not be counting functions of inhomogeneous polytopes of dimension equal to the degree of the quasi-polynomial. It follows that these functions are not, in general, counting functions of lattice points in any scaled convex bodies, even when restricted to single rays. Our results also apply to special rectangular Kronecker coefficients.
A Structural Characterization for Certifying Robinsonian Matrices
Authors: Laurent Monique , Seminaroti Matteo , Tanigawa Shin-ichi 
Published: January 2020

A symmetric matrix is Robinsonian if its rows and columns can be simultaneously reordered in such a way that entries are monotone nondecreasing in rows and columns when moving toward the diagonal. The adjacency matrix of a graph is Robinsonian precisely when the graph is a unit interval graph, so that Robinsonian matrices form a matrix analogue of the class of unit interval graphs. Here we provide a structural characterization for Robinsonian matrices in terms of forbidden substructures, extending the notion of asteroidal triples to weighted graphs. This implies the known characterization of unit interval graphs and leads to an efficient algorithm for certifying that a matrix is not Robinsonian.
Do Triangle-Free Planar Graphs have Exponentially Many $3$-Colorings?
Authors: Dvořák Zdeněk , Sereni Jean-Sébastien 
Published: January 2020

Thomassen conjectured that triangle-free planar graphs have an exponential number of $3$-colorings. We show this conjecture to be equivalent to the following statement: there exists a positive real $\alpha$ such that whenever $G$ is a planar graph and $A$ is a subset of its edges whose deletion makes $G$ triangle-free, there exists a subset $A'$ of $A$ of size at least $\alpha|A|$ such that $G-(A\setminus A')$ is $3$-colorable. This equivalence allows us to study restricted situations, where we can prove the statement to be true.
Parabolic Double Cosets in Coxeter Groups
Authors: Billey Sara C. , Konvalinka Matjaž , Petersen T. Kyle , Slofstra William , Tenner Bridget E. 
Published: January 2020

Parabolic subgroups $W_I$ of Coxeter systems $(W,S)$, as well as their ordinary and double quotients $W / W_I$ and $W_I \backslash W / W_J$, appear in many contexts in combinatorics and Lie theory, including the geometry and topology of generalized flag varieties and the symmetry groups of regular polytopes. The set of ordinary cosets $w W_I$, for $I \subseteq S$, forms the Coxeter complex of $W$, and is well-studied. In this article we look at a less studied object: the set of all double cosets $W_I w W_J$ for $I, J \subseteq S$. Double cosets are not uniquely presented by triples $(I,w,J)$. We describe what we call the lex-minimal presentation, and prove that there exists a unique such object for each double coset. Lex-minimal presentations are then used to enumerate double cosets via a finite automaton depending on the Coxeter graph for $(W,S)$. As an example, we present a formula for the number of parabolic double cosets with a fixed minimal element when $W$ is the symmetric group $S_n$ (in this case, parabolic subgroups are also known as Young subgroups). Our formula is almost always linear time computable in $n$, and we show how it can be generalized to any Coxeter group with little additional work. We spell out formulas for all finite and affine Weyl groups in the case that $w$ is the identity element.
Linear Bound for Majority Colourings of Digraphs
Authors: Knox Fiachra , Šámal Robert 
Published: January 2020

Given $\eta \in [0, 1]$, a colouring $C$ of $V(G)$ is an $\eta$-majority colouring if at most $\eta d^+(v)$ out-neighbours of $v$ have colour $C(v)$, for any $v \in V(G)$. We show that every digraph $G$ equipped with an assignment of lists $L$, each of size at least $k$, has a $2/k$-majority $L$-colouring. For even $k$ this is best possible, while for odd $k$ the constant $2/k$ cannot be replaced by any number less than $2/(k+1)$. This generalizes a result of Anholcer, Bosek and Grytczuk, who proved the cases $k=3$ and $k=4$ and claim a weaker result for general $k$.
Hamiltonicity in Locally Finite Graphs: Two Extensions and a Counterexample
Authors: Heuer Karl 
Published: January 2020

We state a sufficient condition for the square of a locally finite graph to contain a Hamilton circle, extending a result of Harary and Schwenk about finite graphs. We also give an alternative proof of an extension to locally finite graphs of the result of Chartrand and Harary that a finite graph not containing $K^4$ or $K_{2,3}$ as a minor is Hamiltonian if and only if it is $2$-connected. We show furthermore that, if a Hamilton circle exists in such a graph, then it is unique and spanned by the $2$-contractible edges. The third result of this paper is a construction of a graph which answers positively the question of Mohar whether regular infinite graphs with a unique Hamilton circle exist.
q-Stirling Identities Revisited
Authors: Cai Yue , Ehrenborg Richard , Readdy Margaret 
Published: January 2020

We give combinatorial proofs of q-Stirling identities using restricted growth words. This includes a poset theoretic proof of Carlitz's identity, a new proof of the q-Frobenius identity of Garsia and Remmel and of Ehrenborg's Hankel q-Stirling determinantal identity. We also develop a two parameter generalization to unify identities of Mercier and include a symmetric function version.
Measures of Edge-Uncolorability of Cubic Graphs
Authors: Fiol M. A. , Mazzuoccolo G. , Steffen E. 
Published: January 2020

There are many hard conjectures in graph theory, like Tutte's 5-flow conjecture, and the $5$-cycle double cover conjecture, which would be true in general if they would be true for cubic graphs. Since most of them are trivially true for $3$-edge-colorable cubic graphs, cubic graphs which are not $3$-edge-colorable, often called snarks, play a key role in this context. Here, we survey parameters measuring how far apart a non $3$-edge-colorable graph is from being $3$-edge-colorable. We study their interrelation and prove some new results. Besides getting new insight into the structure of snarks, we show that such measures give partial results with respect to these important conjectures. The paper closes with a list of open problems and conjectures.
The Spectral Gap of Graphs Arising From Substring Reversals
Authors: Chung Fan , Tobin Josh 
Published: January 2020

The substring reversal graph $R_n$ is the graph whose vertices are the permutations $S_n$, and where two permutations are adjacent if one is obtained from a substring reversal of the other. We determine the spectral gap of $R_n$, and show that its spectrum contains many integer values. Further we consider a family of graphs that generalize the prefix reversal (or pancake flipping) graph, and show that every graph in this family has adjacency spectral gap equal to one.
Fully Packed Loop Configurations: Polynomiality and Nested Arches
Authors: Aigner Florian 
Published: January 2020

This article proves a conjecture by Zuber about the enumeration of fully packed loops (FPLs). The conjecture states that the number of FPLs whose link pattern consists of two noncrossing matchings which are separated by $m$ nested arches is a polynomial function in $m$ of certain degree and with certain leading coefficient. Contrary to the approach of Caselli, Krattenthaler, Lass and Nadeau (who proved a partial result) we make use of the theory of wheel polynomials developed by Di Francesco, Fonseca and Zinn-Justin. We present a new basis for the vector space of wheel polynomials and a polynomiality theorem in a more general setting. This allows us to finish the proof of Zubers conjecture.
Coboundary Categories and Local Rules
Authors: Westbury Bruce W. 
Published: January 2020

First we develop the theory of local rules for coboundary categories. Then we describe the local rules in two main cases. First for the quantum groups in general and in the seminormal representations of the Hecke algebras. Then for crystals in general and specifically for crystals of minuscule representations. Finally we show how growth diagrams can be extended to construct the action of the cactus group on highest weight words.
Forbidden Subposet Problems for Traces of Set Families
Authors: Gerbner Dániel , Patkós Balázs , Vizer Máté 
Published: January 2020

In this paper we introduce a problem that bridges forbidden subposet and forbidden subconfiguration problems. The sets $F_1,F_2, \dots,F_{|P|}$ form a copy of a poset $P$, if there exists a bijection $i:P\rightarrow \{F_1,F_2, \dots,F_{|P|}\}$ such that for any $p,p'\in P$ the relation $p<_P p'$ implies $i(p)\subsetneq i(p')$. A family $\mathcal{F}$ of sets is $P$-free if it does not contain any copy of $P$. The trace of a family $\mathcal{F}$ on a set $X$ is $\mathcal{F}|_X:=\{F\cap X: F\in \mathcal{F}\}$.We introduce the following notions: $\mathcal{F}\subseteq 2^{[n]}$ is $l$-trace $P$-free if for any $l$-subset $L\subseteq [n]$, the family $\mathcal{F}|_L$ is $P$-free and $\mathcal{F}$ is trace $P$-free if it is $l$-trace $P$-free for all $l\le n$. As the first instances of these problems we determine the maximum size of trace $B$-free families, where $B$ is the butterfly poset on four elements $a,b,c,d$ with $a,b<c,d$ and determine the asymptotics of the maximum size of $(n-i)$-trace $K_{r,s}$-free families for $i=1,2$. We also propose a generalization of the main conjecture of the area of forbidden subposet problems.
Residual $q$-Fano Planes and Related Structures
Authors: Etzion Tuvi , Hooker Niv 
Published: January 2020

One of the most intriguing problems for $q$-analogs of designs, is the existence question of an infinite family of $q$-Steiner systems that are not spreads. In particular the most interesting case is the existence question for the $q$-analog of the Fano plane, known also as the $q$-Fano plane. These questions are in the front line of open problems in block design. There was a common belief and a conjecture that such structures do not exist. Only recently, $q$-Steiner systems were found for one set of parameters. In this paper, a definition for the $q$-analog of the residual design is presented. This new definition is different from previous known definition, but its properties reflect better the $q$-analog properties. The existence of a design with the parameters of the residual $q$-Steiner system in general and the residual $q$-Fano plane in particular are examined. We construct different residual $q$-Fano planes for all $q$, where $q$ is a prime power. The constructed structure is just one step from a construction of a $q$-Fano plane.
Nonexistence of Certain Singly Even Self-Dual Codes with Minimal Shadow
Authors: Bouyuklieva Stefka , Harada Masaaki , Munemasa Akihiro 
Published: January 2020

It is known that there is no extremal singly even self-dual $[n,n/2,d]$ code with minimal shadow for $(n,d)=(24m+2,4m+4)$, $(24m+4,4m+4)$, $(24m+6,4m+4)$, $(24m+10,4m+4)$ and $(24m+22,4m+6)$. In this paper, we study singly even self-dual codes with minimal shadow having minimum weight $d-2$ for these $(n,d)$. For $n=24m+2$, $24m+4$ and $24m+10$, we show that the weight enumerator of a singly even self-dual $[n,n/2,4m+2]$ code with minimal shadow is uniquely determined and we also show that there is no singly even self-dual $[n,n/2,4m+2]$ code with minimal shadow for $m \ge 155$, $m \ge 156$ and $m \ge 160$, respectively. We demonstrate that the weight enumerator of a singly even self-dual code with minimal shadow is not uniquely determined for parameters $[24m+6,12m+3,4m+2]$ and $[24m+22,12m+11,4m+4]$.
The Tu–Deng Conjecture holds Almost Surely
Authors: Spiegelhofer Lukas , Wallner Michael 
Published: January 2020

The Tu–Deng Conjecture is concerned with the sum of digits $w(n)$ of $n$ in base $2$ (the Hamming weight of the binary expansion of $n$) and states the following: assume that $k$ is a positive integer and$1\leqslant t<2^k-1$. Then\[\Bigl \lvert\Bigl\{(a,b)\in\bigl\{0,\ldots,2^k-2\bigr\}^2:a+b\equiv t\bmod 2^k-1, w(a)+w(b)<k\Bigr\}\Bigr \rvert\leqslant 2^{k-1}.\]We prove that the Tu–Deng Conjecture holds almost surely in the following sense: the proportion of $t\in[1,2^k-2]$ such that the above inequality holds approaches $1$ as $k\rightarrow\infty$.Moreover, we prove that the Tu–Deng Conjecture implies a conjecture due to T. W. Cusick concerning the sum of digits of $n$ and $n+t$.
On a Conjecture Regarding Permutations which Destroy Arithmetic Progressions
Authors: Sawhney Mehtaab , Stoner David 
Published: January 2020

Hegarty conjectured for $n\neq 2, 3, 5, 7$ that $\mathbb{Z}/n\mathbb{Z}$ has a permutation which destroys all arithmetic progressions mod $n$. For $n\ge n_0$, Hegarty and Martinsson demonstrated that $\mathbb{Z}/n\mathbb{Z}$ has a permutation destroying arithmetic progressions. However $n_0\approx 1.4\times 10^{14}$ and thus resolving the conjecture in full remained out of reach of any computational techniques. Using constructions modeled after those used by Elkies and Swaminathan for the case of $\mathbb{Z}/p\mathbb{Z}$ with $p$ being prime, this paper establishes the conjecture in full. Furthermore, our results are completely independent of the proof given by Hegarty and Martinsson.
More Turán-Type Theorems for Triangles in Convex Point Sets
Authors: Aronov Boris , Dujmović Vida , Morin Pat , Ooms Aurélien , Xavier da Silveira Luı́s Fernando Schultz 
Published: January 2020

We study the following family of problems: Given a set of $n$ points in convex position, what is the maximum number triangles one can create having these points as vertices while avoiding certain sets of forbidden configurations. As forbidden configurations we consider all 8 ways in which a pair of triangles in such a point set can interact. This leads to 256 extremal Turán-type questions. We give nearly tight (within a $\log n$ factor) bounds for 248 of these questions and show that the remaining 8 questions are all asymptotically equivalent to Stein's longstanding tripod packing problem.
On Upper Transversals in 3-Uniform Hypergraphs
Authors: Henning Michael A. , Yeo Anders 
Published: January 2020

A set $S$ of vertices in a hypergraph $H$ is a transversal if it has a nonempty intersection with every edge of $H$. The upper transversal number $\Upsilon(H)$ of $H$ is the maximum cardinality of a minimal transversal in $H$. We show that if $H$ is a connected $3$-uniform hypergraph of order $n$, then $\Upsilon(H) > 1.4855 \sqrt[3]{n} - 2$. For $n$ sufficiently large, we construct infinitely many connected $3$-uniform hypergraphs, $H$, of order~$n$ satisfying $\Upsilon(H) < 2.5199 \sqrt[3]{n}$. We conjecture that $\displaystyle{\sup_{n \to \infty} \, \left( \inf \frac{ \Upsilon(H) }{ \sqrt[3]{n} } \right) = \sqrt[3]{16} }$, where the infimum is taken over all connected $3$-uniform hypergraphs $H$ of order $n$.