当前期刊: European Journal of Combinatorics Go to current issue    加入关注    本刊投稿指南
显示样式:        排序: IF: - GO 导出
我的关注
我的收藏
您暂时未登录!
登录
  • Kernelization and approximation of distance-r independent sets on nowhere dense graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2021-01-22
    Michał Pilipczuk; Sebastian Siebertz

    For a positive integer r, a distance-r independent set in an undirected graph G is a set I⊆V(G) of vertices pairwise at distance greater than r, while a distance-r dominating set is a set D⊆V(G) such that every vertex of the graph is within distance at most r from a vertex from D. We study the duality between the maximum size of a distance-2r independent set and the minimum size of a distance-r dominating

    更新日期:2021-01-22
  • Combinatorics on lattice paths in strips
    Eur. J. Comb. (IF 0.848) Pub Date : 2021-01-22
    Nancy S.S. Gu; Helmut Prodinger

    For lattice paths in strips which begin at (0,0) and have only up steps U:(i,j)→(i+1,j+1) and down steps D:(i,j)→(i+1,j−1), let An,k denote the set of paths of length n which start at (0,0), end on heights 0 or −1, and are contained in the strip −⌊k+12⌋≤y≤⌊k2⌋ of width k, and let Bn,k denote the set of paths of length n which start at (0,0) and are contained in the strip 0≤y≤k. We establish a bijection

    更新日期:2021-01-22
  • Rigid realizations of graphs with few locations in the plane
    Eur. J. Comb. (IF 0.848) Pub Date : 2021-01-14
    Csaba Király

    Adiprasito and Nevo (2018) proved that there exists a set of 76 points in R3 such that every triangulated planar graph has an infinitesimally rigid realization in which each vertex is mapped to a point in this set. In this paper we show that there exists a set of 26 points in the plane such that every planar graph which is generically rigid in R2 has an infinitesimally rigid realization in which each

    更新日期:2021-01-14
  • On the Standard (2,2)-Conjecture
    Eur. J. Comb. (IF 0.848) Pub Date : 2021-01-08
    Jakub Przybyło

    The well-known 1–2–3 Conjecture asserts that the edges of every graph without an isolated edge can be weighted with 1, 2 and 3 so that adjacent vertices receive distinct weighted degrees. This is open in general. The Standard (2,2)-Conjecture asserts that every graph with no isolated edge and no isolated triangle can be decomposed into two graphs, each of which can be weighted with 1, 2 for the same

    更新日期:2021-01-10
  • Remarks on the Erdős Matching Conjecture for vector spaces
    Eur. J. Comb. (IF 0.848) Pub Date : 2021-01-08
    Ferdinand Ihringer

    In 1965, Paul Erdős asked about the largest family Y of k-sets in {1,…,n} such that Y does not contain s+1 pairwise disjoint sets. This problem is commonly known as the Erdős Matching Conjecture. We investigate the q-analog of this question, that is we want to determine the size of a largest family Y of k-spaces in Fqn such that Y does not contain s+1 pairwise disjoint k-spaces. Here we call two subspaces

    更新日期:2021-01-08
  • Atoms for signed permutations
    Eur. J. Comb. (IF 0.848) Pub Date : 2021-01-06
    Zachary Hamaker; Eric Marberg

    There is a natural analogue of weak Bruhat order on the involutions in any Coxeter group. The saturated chains of intervals in this order correspond to reduced words for a certain set of group elements called atoms. Brion gives a general formula for the cohomology class of a K-orbit closure in an arbitrary flag variety, where K is a symmetric subgroup of a complex algebraic group. In type A, the terms

    更新日期:2021-01-06
  • Entire coloring of 2-connected plane graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2021-01-04
    Weifan Wang; Xiaoxue Hu; Yiqiao Wang

    The entire chromatic number χvef(G) of a plane graph G is the least number of colors such that any two adjacent or incident elements in V(G)∪E(G)∪F(G) receive different colors. In this paper, we prove that every 2-connected simple plane graph G with maximum degree Δ≥20 has χvef(G)=Δ+1.

    更新日期:2021-01-04
  • Cyclic coloring of plane graphs with maximum face size 16 and 17
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-30
    Zdeněk Dvořák; Michael Hebdige; Filip Hlásek; Daniel Král’; Jonathan A. Noel

    Plummer and Toft conjectured in 1987 that the vertices of every 3-connected plane graph with maximum face size Δ⋆ can be colored using at most Δ⋆+2 colors in such a way that no face is incident with two vertices of the same color. The conjecture has been proven for Δ⋆=3, Δ⋆=4 and Δ⋆≥18. We prove the conjecture for Δ⋆=16 and Δ⋆=17.

    更新日期:2020-12-31
  • Connectivity of orientations of 3-edge-connected graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-24
    Florian Hörsch; Zoltán Szigeti

    We attempt to generalize a theorem of Nash-Williams stating that a graph has a k-arc-connected orientation if and only if it is 2k-edge-connected. In a strongly connected digraph we call an arc deletable if its deletion leaves a strongly connected digraph. Given a 3-edge-connected graph G, we define its Frank number f(G) to be the minimum number k such that there exist k orientations of G with the

    更新日期:2020-12-24
  • Integer sets with identical representation functions, II
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-23
    Shi-Qiang Chen; Yong-Gao Chen

    Let N be the set of all nonnegative integers. For S⊆N and n∈N, let RS(n) denote the number of solutions of the equation n=s+s′, s,s′∈S, s

    更新日期:2020-12-23
  • Enumeration of various animals on the triangular lattice
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-22
    Toufik Mansour; Reza Rastegar

    In this paper, we consider various classes of polyiamonds that are animals residing on the triangular lattice. By careful analyses through certain layer-by-layer decompositions and cell pruning/growing arguments, we derive explicit forms for the generating functions of the number of nonempty translation-invariant baryiamonds (bargraphs in the triangular lattice), column-convex polyiamonds, and convex

    更新日期:2020-12-22
  • On Rado conditions for nonlinear Diophantine equations
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-17
    Jordan Mitchell Barrett; Martino Lupini; Joel Moreira

    Building on previous work of Di Nasso and Luperi Baglini, we provide general necessary conditions for a Diophantine equation to be partition regular. These conditions are inspired by Rado’s characterization of partition regular linear homogeneous equations. We conjecture that these conditions are also sufficient for partition regularity, at least for equations whose corresponding monovariate polynomial

    更新日期:2020-12-17
  • Principal specializations of Schubert polynomials and pattern containment
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-17
    Yibo Gao

    The principal specialization νw=Sw(1,…,1) of the Schubert polynomial at w, which equals the degree of the matrix Schubert variety corresponding to w, has attracted a lot of attention in recent years. In this paper, we show that νw is bounded below by 1+p132(w)+p1432(w) where pu(w) is the number of occurrences of the pattern u in w, strengthening a previous result by A. Weigandt. We then make a conjecture

    更新日期:2020-12-17
  • Determinantal and Pfaffian identities for ninth variation skew Schur functions and Q-functions
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-16
    Angèle M. Foley; Ronald C. King

    Recently Okada defined algebraically ninth variation skew Q-functions, in parallel to Macdonald’s ninth variation skew Schur functions. Here we introduce a skew shifted tableaux definition of these ninth variation skew Q-functions, and prove by means of a non-intersecting lattice path model a Pfaffian outside decomposition result in the form of a ninth variation version of Hamel’s Pfaffian outside

    更新日期:2020-12-16
  • Graph covers with two new eigenvalues
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-14
    Chris Godsil; Maxwell Levit; Olha Silina

    A certain signed adjacency matrix of the hypercube, which Hao Huang used last year to resolve the Sensitivity Conjecture, is closely related to the unique, 4-cycle free, 2-fold cover of the hypercube. We develop a framework in which this connection is a natural first example of the relationship between group valued adjacency matrices with few eigenvalues, and combinatorially interesting covering graphs

    更新日期:2020-12-15
  • A linear hypergraph extension of the bipartite Turán problem
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-15
    Guorong Gao; An Chang

    An r-uniform hypergraph is linear if every two edges intersect in at most one vertex. Given a family of r-uniform hypergraphs F, the linear Turán number exrlin(n,F) is the maximum number of edges of a linear r-uniform hypergraph on n vertices that does not contain any member of F as a subhypergraph. Given a graph F and a positive integer r≥2, the r-expansion of F is the r-graph F+ obtained from F by

    更新日期:2020-12-15
  • On 12̲0-avoiding inversion and ascent sequences
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-14
    Zhicong Lin; Shishuo Fu

    Recently, Yan and the first author investigated systematically the enumeration of inversion or ascent sequences avoiding vincular patterns of length 3, where two of the three letters are required to be adjacent. They established many connections with familiar combinatorial families and proposed several interesting conjectures. The main objective of this paper is to prove two of their conjectures concerning

    更新日期:2020-12-14
  • Defective DP-colorings of sparse multigraphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-14
    Yifan Jing; Alexandr Kostochka; Fuhong Ma; Pongpat Sittitrai; Jingwei Xu

    DP-coloring (also known as correspondence coloring) is a generalization of list coloring developed recently by Dvořák and Postle. We introduce and study (i,j)-defective DP-colorings of multigraphs. We concentrate on sparse multigraphs and consider fDP(i,j,n) — the minimum number of edges that may have an n-vertex (i,j)-critical multigraph, that is, a multigraph G that has no (i,j)-defective DP-coloring

    更新日期:2020-12-14
  • Tilings in graphons
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-11
    Jan Hladký; Ping Hu; Diana Piguet

    We introduce a counterpart to the notion of tilings, that is vertex-disjoint copies of a fixed graph F, to the setting of graphons. The case F=K2 gives the notion of matchings in graphons. We give a transference statement that allows us to switch between the finite and limit notion, and derive several favorable properties, including the LP-duality counterpart to the classical relation between the fractional

    更新日期:2020-12-13
  • Alternating multiple zeta values, and explicit formulas of some Euler–Apéry-type series
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-11
    Weiping Wang; Ce Xu

    In this paper, we study some Euler–Apéry-type series which involve central binomial coefficients and (generalized) harmonic numbers. In particular, we establish elegant explicit formulas of some series by iterated integrals and alternating multiple zeta values. Based on these formulas, we further show that some other series are reducible to ln(2), zeta values, and alternating multiple zeta values by

    更新日期:2020-12-13
  • Lovász–Saks–Schrijver ideals and parity binomial edge ideals of graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-11
    Arvind Kumar

    Let G be a simple graph on n vertices. Let LG and IG denote the Lovász–Saks–Schrijver(LSS) ideal and parity binomial edge ideal of G in the polynomial ring S=K[x1,…,xn,y1,…,yn] respectively. We classify graphs whose LSS ideals and parity binomial edge ideals are complete intersections. We also classify graphs whose LSS ideals and parity binomial edge ideals are almost complete intersections, and we

    更新日期:2020-12-13
  • Curves on surfaces and surgeries
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-11
    Abdoul Karim Sane

    In this paper, we introduce a new surgery operation on the set of collections of curves, on a closed oriented surface, whose complement is a topological disk. We prove that any two such collections can be connected by a sequence of surgeries.

    更新日期:2020-12-13
  • Fertility monotonicity and average complexity of the stack-sorting map
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-10
    Colin Defant

    Let Dn denote the average number of iterations of West’s stack-sorting map s that are needed to sort a permutation in Sn into the identity permutation 123⋯n. We prove that 0.62433≈λ≤lim infn→∞Dnn≤lim supn→∞Dnn≤35(7−8log2)≈0.87289, where λ is the Golomb–Dickman constant. Our lower bound improves upon West’s lower bound of 0.23, and our upper bound is the first improvement upon the trivial upper bound

    更新日期:2020-12-10
  • Analogues of Milner’s Theorem for families without long chains and of vector spaces
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-10
    Peter Frankl

    Let n>k>0 be integers and X an n-element set. A family F consisting of subsets of X is called k-Sperner if it has no distinct members F0,…,Fk such that F0⊂F1⊂…⊂Fk. A family is called s-union if the union of any two of its members has size at most s. A classical result of Milner determines the maximum size of a family that is both 1-Sperner and s-union. The present paper is dealing with the case k≥2

    更新日期:2020-12-10
  • On the asymptotic growth of the number of tree-child networks
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-10
    Michael Fuchs; Guan-Ru Yu; Louxin Zhang

    In a recent paper, McDiarmid, Semple, and Welsh (2015) showed that the number of tree-child networks with n leaves has the factor n2n in its main asymptotic growth term. In this paper, we improve this by completely identifying the main asymptotic growth term up to a constant. More precisely, we show that the number of tree-child networks with n leaves grows like Θn−2∕3ea1(3n)1∕312e2nn2n,where a1=−2

    更新日期:2020-12-10
  • Finite 3-set-homogeneous graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-10
    Jin-Xin Zhou

    In this paper, all graphs are assumed to be finite. Let s≥1 be an integer. A graph is called s-CSH (s-connected-set-homogeneous) if for every pair of isomorphic connected induced subgraphs on at most s vertices, there exists an automorphism mapping the first to the second. A graph is called s-SH (s-set-homogeneous) if for every pair of isomorphic induced subgraphs (not necessarily connected) on at

    更新日期:2020-12-10
  • Representations of torsion-free arithmetic matroids
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-10
    Roberto Pagaria; Giovanni Paolini

    We study the representability problem for torsion-free arithmetic matroids. After introducing a “strong gcd property” and a new operation called “reduction”, we describe and implement an algorithm to compute all essential representations, up to equivalence. As a consequence, we obtain an upper bound to the number of equivalence classes of representations. In order to rule out equivalent representations

    更新日期:2020-12-10
  • Counterexamples to a conjecture by Gross, Mansour and Tucker on partial-dual genus polynomials of ribbon graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-09
    Qi Yan; Xian’an Jin

    Gross, Mansour and Tucker introduced the partial-dual orientable genus polynomial and the partial-dual Euler genus polynomial. They computed these two partial-dual genus polynomials of four families of ribbon graphs, posed some research problems and made some conjectures. In this paper, we introduce the notion of signed interlace sequences of bouquets and obtain the partial-dual Euler genus polynomials

    更新日期:2020-12-09
  • A note on sublinear separators and expansion
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-04
    Zdeněk Dvořák

    For a hereditary class G of graphs, let sG(n) be the minimum function such that each n-vertex graph in G has a balanced separator of order at most sG(n), and let ∇G(r) be the minimum function bounding the expansion of G, in the sense of bounded expansion theory of Nešetřil and Ossona de Mendez. The results of Plotkin et al. (1994) and Esperet and Raymond (2018) imply that if sG(n)=Θ(n1−ε) for some

    更新日期:2020-12-04
  • Trees, parking functions and factorizations of full cycles
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-12-02
    John Irving; Amarpreet Rattan

    Parking functions of length n are well known to be in correspondence with both labelled trees on n+1 vertices and factorizations of the full cycle σn=(01…n) into n transpositions. In fact, these correspondences can be refined: Kreweras equated the area enumerator of parking functions with the inversion enumerator of labelled trees, while an elegant bijection of Stanley maps the area of parking functions

    更新日期:2020-12-02
  • Coloring near-quadrangulations of the cylinder and the torus
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-11-11
    Zdeněk Dvořák; Jakub Pekárek

    Let G be a simple connected plane graph and let C1 and C2 be cycles in G bounding distinct faces f1 and f2. For a positive integer ℓ, let r(ℓ) denote the number of integers n such that −ℓ≤n≤ℓ, n is divisible by 3, and n has the same parity as ℓ; in particular, r(4)=1. Let rf1,f2(G)=∏fr(|f|), where the product is over the faces f of G distinct from f1 and f2, and let q(G)=1+∑f:|f|≠4|f|, where the sum

    更新日期:2020-11-12
  • Percolating sets in bootstrap percolation on the Hamming graphs and triangular graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-10-21
    Mohammadreza Bidgoli; Ali Mohammadian; Behruz Tayfeh-Rezaie

    The r-neighbor bootstrap percolation on a graph is an activation process of the vertices. The process starts with some initially activated vertices and then, in each round, any inactive vertex with at least r active neighbors becomes activated. A set of initially activated vertices leading to the activation of all vertices is said to be a percolating set. Denote the minimum size of a percolating set

    更新日期:2020-10-30
  • Toughness in pseudo-random graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-10-13
    Xiaofeng Gu

    A d-regular graph on n vertices with the second largest absolute eigenvalue at most λ is called an (n,d,λ)-graph. The celebrated expander mixing lemma for (n,d,λ)-graphs builds a connection between graph spectrum and edge distribution. In this paper, we present some applications of the expander mixing lemma. In particular, we make progress toward the toughness conjecture of Brouwer. The toughness t(G)

    更新日期:2020-10-15
  • Finiteness theorems for matroid complexes with prescribed topology
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-26
    Federico Castillo; José Alejandro Samper

    There are finitely many simplicial complexes (up to isomorphism) with a given number of vertices. Translating this fact to the language of h-vectors, there are finitely many simplicial complexes of bounded dimension with h1=k for any natural number k. In this paper we study the question at the other end of the h-vector: Are there only finitely many (d−1)-dimensional simplicial complexes with hd=k for

    更新日期:2020-09-28
  • On-line size Ramsey number for monotone k-uniform ordered paths with uniform looseness
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-24
    Xavier Pérez-Giménez; Paweł Prałat; Douglas B. West

    An ordered hypergraph is a hypergraph H with a specified linear ordering of the vertices, and the appearance of an ordered hypergraph G in H must respect the specified order on V(G). In on-line Ramsey theory, Builder iteratively presents edges that Painter must immediately color. The t-color on-line size Ramsey number R̃t(G) of an ordered hypergraph G is the minimum number of edges Builder needs to

    更新日期:2020-09-24
  • 3-regular graphs are 2-reconstructible
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-22
    Alexandr V. Kostochka; Mina Nahvi; Douglas B. West; Dara Zirlin

    A graph is ℓ-reconstructible if it is determined by its multiset of induced subgraphs obtained by deleting ℓ vertices. We prove that 3-regular graphs are 2-reconstructible.

    更新日期:2020-09-23
  • r-hued (r+1)-coloring of planar graphs with girth at least 8 for r≥9
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-18
    Hoang La; Mickael Montassier; Alexandre Pinlou; Petru Valicov

    Let r,k≥1 be two integers. An r-hued k-coloring of the vertices of a graph G=(V,E) is a proper k-coloring of the vertices, such that, for every vertex v∈V, the number of colors in its neighborhood is at least min{dG(v),r}, where dG(v) is the degree of v. We prove the existence of an r-hued (r+1)-coloring for planar graphs with girth at least 8 for r≥9. As a corollary, every planar graph with maximum

    更新日期:2020-09-20
  • On the size of shadow-added intersecting families
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-16
    Peter Frankl

    Let n≥2k−1>1, [n]={1,2,…,n}. For a family F of k-subsets of [n] let ∂F be the immediate shadow (cf. Definition 1.1) of F. Suppose that |F∩F′|≥2 for all F,F′∈F. We conjecture that |F|+|∂F|≤3n−2k−2+n−2k−3 and prove it for n=2k−1, n≥3(k−1) and also for k≤10. This problem is somewhat unusual but we exhibit deep connections to the Erdős–Ko–Rado Theorem and to the Erdős Matching Conjecture. Some related

    更新日期:2020-09-16
  • Lattice paths and branched continued fractions II. Multivariate Lah polynomials and Lah symmetric functions
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-15
    Mathias Pétréolle, Alan D. Sokal

    We introduce the generic Lah polynomials Ln,k(ϕ), which enumerate unordered forests of increasing ordered trees with a weight ϕi for each vertex with i children. We show that, if the weight sequence ϕ is Toeplitz-totally positive, then the triangular array of generic Lah polynomials is totally positive and the sequence of row-generating polynomials Ln(ϕ,y) is coefficientwise Hankel-totally positive

    更新日期:2020-09-15
  • Counting primitive subsets and other statistics of the divisor graph of {1,2,…,n}
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-09
    Nathan McNew

    Let Q(n) denote the count of the primitive subsets of the integers {1,2…,n}. We give a new proof that Q(n)=α(1+o(1))n for some constant α, which allows us to give a good error term and to improve upon the lower bound for the value of α. We also show that the method developed can be applied to many similar problems related to the divisor graph, including other questions about primitive sets, geomet

    更新日期:2020-09-09
  • Graphs that contain multiply transitive matchings
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-07
    Alex Schaefer, Eric Swartz

    Let Γ be a finite, undirected, connected, simple graph. We say that a matching M is a permutable m-matching if M contains m edges and the subgroup of Aut(Γ) that fixes the matching M setwise allows the edges of M to be permuted in any fashion. A matching M is 2-transitive if the setwise stabilizer of M in Aut(Γ) can map any ordered pair of distinct edges of M to any other ordered pair of distinct edges

    更新日期:2020-09-07
  • Blowup Ramsey numbers
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-07
    Victor Souza

    We study a generalisation of the bipartite Ramsey numbers to blowups of graphs. For a graph G, denote the t-blowup of G by G[t]. We say that G is r-Ramsey for H, and write G→rH, if every r-colouring of the edges of G has a monochromatic copy of H. We show that if G→rH, then for all t, there exists n such that G[n]→rH[t]. In fact, we provide exponential lower and upper bounds for the minimum n with

    更新日期:2020-09-07
  • The γ-positivity of bivariate Eulerian polynomials via the Hetyei–Reiner action
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-04
    Hua Sun

    The bivariate Eulerian polynomials are defined by An(p,q)=∑π∈Snpodes(π)qedes(π),where odes(π) and edes(π) are the number of descents of permutation π in odd and even positions, respectively. In this paper, by the Hetyei–Reiner action, we show that for k≥1, the bivariate Eulerian polynomials A2k+1(p,q) and (1+p)−1A2k(p,q) are γ-positive, namely, they can be expressed in terms of the basis Bn≔{(pq)i

    更新日期:2020-09-04
  • Signed Euler–Mahonian identities
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-03
    Sen-Peng Eu; Zhicong Lin; Yuan-Hsun Lo

    A relationship between signed Eulerian polynomials and the classical Eulerian polynomials on Sn was given by Désarménien and Foata in 1992, and a refined version, called signed Euler–Mahonian identity, together with a bijective proof was proposed by Wachs in the same year. By generalizing this bijection, in this paper we extend the above results to the Coxeter groups of types Bn, Dn, and the complex

    更新日期:2020-09-03
  • 2-connected chordal graphs and line graphs are (1,5)-choosable
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-03
    Tsai-Lien Wong

    Suppose G is a graph and k,k′ are positive integers. A (k,k′)-list assignment is a mapping L which assigns to each vertex v a set L(v) of k real numbers, and assigns to each edge e a set L(e) of k′ real numbers. A proper L-total weighting is a mapping ϕ:V(G)∪E(G)→R such that ϕ(z)∈L(z) for z∈V∪E, and ∑e∈E(u)ϕ(e)+ϕ(u)≠∑e∈E(v)ϕ(e)+ϕ(v) for every edge uv. A graph G is called (k,k′)-choosable if for every

    更新日期:2020-09-03
  • On circular-perfect graphs: A survey
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-02
    Arnaud Pêcher; Annegret K. Wagler

    Circular-perfect graphs form a natural superclass of perfect graphs, introduced by Zhu almost 20 years ago: on the one hand due to their definition by means of a more general coloring concept, on the other hand as an important class of χ-bound graphs with the smallest non-trivial χ-binding function χ(G)≤ω(G)+1. In this paper, we survey the results about circular-perfect graphs obtained in the two last

    更新日期:2020-09-02
  • On the 4-color theorem for signed graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-02
    František Kardoš; Jonathan Narboni

    Máčajová et al. (2016) defined the chromatic number of a signed graph which coincides for all-positive signed graphs with the chromatic number of unsigned graphs. They conjectured that in this setting, for signed planar graphs four colors are always enough, generalizing thereby The Four Color Theorem. We disprove the conjecture.

    更新日期:2020-09-02
  • Random hypergraphs and property B
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-02
    Lech Duraj; Jakub Kozik; Dmitry Shabanov

    In 1964 Erdős proved that (1+o1)eln(2)4k22k edges are sufficient to build a k-graph which is not two colorable. To this day, it is not known whether there exist such k-graphs with smaller number of edges. Erdős’ bound is consequence of the fact that a hypergraph with k2∕2 vertices and M(k)=(1+o1)eln(2)4k22k randomly chosen edges of size k is asymptotically almost surely not two colorable. Our first

    更新日期:2020-09-02
  • Superposition of snarks revisited
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-09-01
    Edita Máčajová; Martin Škoviera

    In this paper we propose a new approach to superposition of snarks, a powerful method of constructing large cubic graphs with no 3-edge-colouring from small ones. The main idea is to use surjective mappings between graphs similar to graph homomorphisms and to control flows induced from the domain graph to the target graph via the mappings. This leads to significant strengthening of the power of the

    更新日期:2020-09-01
  • Homomorphisms of signed graphs: An update
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-08-28
    Reza Naserasr; Éric Sopena; Thomas Zaslavsky

    A signed graph is a graph together with an assignment of signs to the edges. A closed walk in a signed graph is said to be positive (negative) if it has an even (odd) number of negative edges, counting repetition. Recognizing the signs of closed walks as one of the key structural properties of a signed graph, we define a homomorphism of a signed graph (G,σ) to a signed graph (H,π) to be a mapping of

    更新日期:2020-08-28
  • The last temptation of William T. Tutte
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-08-27
    Bojan Mohar; Nathan Singer

    In 1999, at one of his last public lectures, Tutte discussed a question he had considered since the times of the Four Color Conjecture. He asked whether the 4-coloring complex of a planar triangulation could have two components in which all colorings had the same parity. In this note we answer Tutte’s question contrary to his speculations by showing that there are triangulations of the plane whose

    更新日期:2020-08-28
  • Optimal radio-k-labelings of trees
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-08-27
    Angel Chavez; Daphne Der-Fen Liu; Mason Shurman

    Let G be a graph, and let k be a positive integer. The radio-k-number of G is the smallest integer s for which there exists a function f:V(G)→{0,1,2,…,s} such that for any two vertices u,v∈V(G), |f(u)−f(v)|⩾k+1−d(u,v), where d(u,v) is the distance between u and v. In particular, when d is the diameter of G, the radio-d-number is called the radio number of G. This article contains four major parts.

    更新日期:2020-08-27
  • On-line partitioning of width w posets into wO(loglogw) chains
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-08-27
    Bartłomiej Bosek; Tomasz Krawczyk

    An on-line chain partitioning algorithm receives the elements of a poset one at a time, and when an element is received, irrevocably assigns it to one of the chains. In this paper, we present an on-line algorithm that partitions posets of width w into wO(loglogw) chains. This improves over previously best known algorithms using wO(logw) chains by Bosek and Krawczyk and by Bosek, Kierstead, Krawczyk

    更新日期:2020-08-27
  • Odd decompositions and coverings of graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-08-26
    Mirko Petruševski; Riste Škrekovski

    A (finite) graph is odd if all its vertices have odd degrees. The principal aim of this survey is to present the current state of research on covers and decompositions of graphs into fewest possible number of odd subgraphs. Given a graph G, the parameters χo′(G) and covo(G) denote, respectively, the minimum size of a decomposition and cover of G consisting of odd subgraphs. Pyber (1991) and Mátrai

    更新日期:2020-08-27
  • On subgroup perfect codes in Cayley graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-08-25
    Junyang Zhang; Sanming Zhou

    A perfect code in a graph Γ=(V,E) is a subset C of V such that no two vertices in C are adjacent and every vertex in V∖C is adjacent to exactly one vertex in C. A subgroup H of a group G is called a subgroup perfect code of G if there exists a Cayley graph of G which admits H as a perfect code. Equivalently, H is a subgroup perfect code of G if there exists an inverse-closed subset A of G containing

    更新日期:2020-08-25
  • Stable structure on safe set problems in vertex-weighted graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-08-25
    Shinya Fujita; Boram Park; Tadashi Sakuma

    Let G be a graph, and let w be a positive real-valued weight function on V(G). For every subset S of V(G), let w(S)=∑v∈Sw(v). A non-empty subset S⊂V(G) is a weighted safe set of (G,w) if, for every component C of the subgraph induced by S and every component D of G−S, we have w(C)≥w(D) whenever there is an edge between C and D. If the subgraph of G induced by a weighted safe set S is connected, then

    更新日期:2020-08-25
  • An analogue of the Erdős–Gallai theorem for random graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-08-25
    József Balogh; Andrzej Dudek; Lina Li

    Recently, variants of many classical extremal theorems have been proved in the random environment. We, complementing existing results, extend the Erdős–Gallai Theorem in random graphs. In particular, we determine, up to a constant factor, the maximum number of edges in a Pn-free subgraph of G(N,p), practically for all values of N,n and p. Our work is also motivated by the recent progress on the size-Ramsey

    更新日期:2020-08-25
  • Classes of graphs with low complexity: The case of classes with bounded linear rankwidth
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-08-24
    Jaroslav Nešetřil; Patrice Ossona de Mendez; Roman Rabinovich; Sebastian Siebertz

    Classes with bounded rankwidth are MSO-transductions of trees and classes with bounded linear rankwidth are MSO-transductions of paths – a result that shows a strong link between the properties of these graph classes considered from the point of view of structural graph theory and from the point of view of finite model theory. We take both views on classes with bounded linear rankwidth and prove structural

    更新日期:2020-08-25
  • Concepts of signed graph coloring
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-08-24
    Eckhard Steffen; Alexander Vogel

    This paper surveys recent development of concepts related to coloring of signed graphs. Various approaches are presented and discussed.

    更新日期:2020-08-25
  • On 2-defective DP-colorings of sparse graphs
    Eur. J. Comb. (IF 0.848) Pub Date : 2020-08-24
    Alexandr Kostochka; Jingwei Xu

    Introduced by Dvořák and Postle, the notion of DP-coloring generalizes list coloring and helps to prove new results on list coloring. We consider 1-defective and 2-defective DP-colorings of graphs with 2 colors. For j=1,2, we find exact lower bounds on the number of edges in (j,2)-DP-critical graphs (that is, graphs that do not admit j-defective DP-colorings with 2 colors but whose every proper subgraph

    更新日期:2020-08-24
Contents have been reproduced by permission of the publishers.
导出
全部期刊列表>>
微生物研究
虚拟特刊
亚洲大洋洲地球科学
NPJ欢迎投稿
自然科研论文编辑
ERIS期刊投稿
欢迎阅读创刊号
自然职场,为您触达千万科研人才
spring&清华大学出版社
城市可持续发展前沿研究专辑
Springer 纳米技术权威期刊征稿
全球视野覆盖
施普林格·自然新
chemistry
物理学研究前沿热点精选期刊推荐
自然职位线上招聘会
欢迎报名注册2020量子在线大会
化学领域亟待解决的问题
材料学研究精选新
GIANT
ACS ES&T Engineering
ACS ES&T Water
屿渡论文,编辑服务
阿拉丁试剂right
上海中医药大学
浙江大学
西湖大学
化学所
北京大学
山东大学
隐藏1h前已浏览文章
课题组网站
新版X-MOL期刊搜索和高级搜索功能介绍
ACS材料视界
南方科技大学
南开大学
浙江大学
天合科研
x-mol收录
试剂库存
down
wechat
bug