Kolja Knauer, Ulrich Knauer
In this note we study embeddings of Cayley graphs of right groups on surfaces. We characterize those right groups which have a toroidal but no planar Cayley graph, such that the generating system of the right group has a minimal generating system of the group as a factor.
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Toroidal embeddings of cubic projective plane obstructions
本文对六个三次射影平面障碍图在环面中的嵌入进行了等价分类，完善了 Glover 和 Huneke 关于三次图射影平面嵌入障碍的结果。
Embeddability of hieroglyphs in the torus and the intersection form
本文研究单顶点带图的环面嵌入问题，给出其可嵌入环面的判定准则，从而解决 Skopenkov 提出的相关问题。
A Kempe swap in a proper coloring interchanges the colors on some maximal connected 2-colored subgraph. Two $k$-colorings are $k$-equivalent if we can transform one into the other using Kempe swaps. The triangulated toroidal grid, $T[m\times n]$, is formed from (a toroidal embedding of) the Cartesian product of $C_m$ and $C_n$ by adding parallel diagonals inside all 4-faces. Mohar and Salas showed that not all 4-colorings of $T[m\times n]$ are 4-equivalent. In contrast, Bonamy, Bousquet, Feghali, and Johnson showed that all 6-colorings of $T[m\times n]$ are 6-equivalent. They asked whether the…
We investigate the toroidal expanse of an embedded graph G, that is, the size of the largest toroidal grid contained in G as a minor. In the course of this work we introduce a new embedding density parameter, the stretch of an embedded graph G, and use it to bound the toroidal expanse from above and from below within a constant factor depending only on the genus and the maximum degree. We also show that these parameters are tightly related to the planar crossing number of G. As a consequence of our bounds, we derive an efficient constant factor approximation algorithm for the toroidal expanse …
The Cartesian product of two cycles (of length m and length n) has a natural embedding on the torus, such that each face of the embedding is a 4-cycle. The toroidal grid Qd(m,n,r) is a generalization of this in which there is a shift by r when traversing the meridian of length m. In 2008, Steve Wilson found two interesting infinite families of (nonbipartite) toroidal grids that are unstable. (By definition, this means that the canonical bipartite double cover of the grid has more than twice as many automorphisms as the grid has.) It is easy to see that bipartite grids are also unstable, becaus…
It's well known that every planar graph is $4$-colorable. A toroidal graph is a graph that can be embedded on a torus. It's proved that every toroidal graph is $7$-colorable. A proper coloring of a graph is called \emph{odd} if every non-isolated vertex has at least one color that appears an odd number of times in its neighborhood. The smallest number of colors that admits an odd coloring of a graph $ G $ is denoted by $χ_{o}(G)$. In this paper, we prove that if $G$ is tortoidal, then $χ_{o}\left({G}\right)\le9$; Note that $K_7$ is a toroidal graph, the upper bound is no less than $7$.
A note on the Nearly Dispersability of Odd Toroidal Grids
本文在作者先前确定奇环面网格近乎可分散性结果的基础上，进一步为该结果提供了一个简要的证明。
Planar-Toroidal Decomposition of $K_{12}$
研究证明K12无法分解为一个平面图和一个扭面图，并揭示了平面图与扭面图边数的关系。
A Schnyder wood is an orientation and coloring of the edges of a planar map satisfying a simple local property. We propose a generalization of Schnyder woods to graphs embedded on the torus with application to graph drawing. We prove several properties on this new object. Among all we prove that a graph embedded on the torus admits such a Schnyder wood if and only if it is an essentially 3-connected toroidal map. We show that these Schnyder woods can be used to embed the universal cover of an essentially 3-connected toroidal map on an infinite and periodic orthogonal surface. Finally we use th…
In this paper, we analyze embeddings of grid graphs on orientable surfaces. We determine the genus of a large class of k-dimensional grid graphs and effective two-sided bounds for the genus of any 3-dimensional grid graph, both in terms of a grid graph's combinatorics. As an application, we provide a complete classification of planar and toroidal grid graphs. Our work requires a variety of combinatorial arguments to determine effective lower bounds on the genus of a grid graph, along with explicitly constructing embeddings of grid graphs on surfaces to determine effective upper bounds on their…
We describe the structure of 2-connected non-planar toroidal graphs with no K_{3,3}-subdivisions, using an appropriate substitution of planar networks into the edges of certain graphs called toroidal cores. The structural result is based on a refinement of the algorithmic results for graphs containing a fixed K_5-subdivision in [A. Gagarin and W. Kocay, "Embedding graphs containing K_5-subdivisions'', Ars Combin. 64 (2002), 33-49]. It allows to recognize these graphs in linear-time and makes possible to enumerate labelled 2-connected toroidal graphs containing no K_{3,3}-subdivisions and havin…
In this paper, we study the embedding of a complete balanced $d$-partite $d$-uniform hypergraph with all its $nd$ vertices represented as points in general position in $\mathbb{R}^d$ and each hyperedge drawn as a convex hull of $d$ corresponding vertices. We assume that the set of vertices is partitioned into $d$ disjoint sets, each of size $n$, such that each of the vertices in a hyperedge is from a different set. Two hyperedges are said to be crossing if they are vertex disjoint and contain a common point in their relative interiors. Using the Generalized Colored Tverberg Theorem, we observe…
Embedding problem between right-angled Artin groups
本文基于拟中位图的几何观点，研究如何判断两个有限图对应的直角 Artin 群之间是否存在子群嵌入关系，内容为 CIRM 迷你课程讲义。
The Right Angled Artin Group Functor as a Categorical Embedding
本文证明可通过纯代数方式在群中刻画直角 Artin 群，并在群同态中刻画图同态，进而给出从 raag 恢复原图的新算法。
Maximizing copies of a fixed graph in graphs with a prescribed number of edges
研究在规定边数的图中最大化固定图副本数的问题，通过相关结果确定了特定图\(H\)的\(\operatorname{emb}(H,{\binom{n}{2}})\)值，还证明除匹配图外，\(K_n\)是使嵌入数最大的唯一图，刻画了\(K_n\)达最大嵌入数的图。
Orthogonal and oriented Fano planes, triangular embeddings of $K_7,$ and geometrical representations of the Frobenius group $F_{21}$
本文研究21阶Frobenius群F21的几何表示，证明两个正交Fano平面的公共自同构群与适当定向Fano平面的自同构群均同构于F21，并证明K7的任意三角嵌入同构于经典环面双嵌入且面2-可着色，从而给出F21的三种几何表示。
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