Completion of topological loops

A Hausdorff topological group equipped with the right uniformity admits a group completion iff the inversion mapping preserves Cauchy filters, cf. [1], III. §3, No.5, Théorème 1. Up until today a general theorem on the completion of topological loops is not available, for partial results see [9], [10]. This is among others due to the fact that topological loops will not necessarily have a compatible right uniformity. The main results (6–8) of this paper are the following: All topological loops are locally uniform in the sense of [11], and, provided the notion of “Cauchy filter” is suitably chosen, they can be completed. An analogue of the completion theorem for groups cited above holds for topological loops. According to these aims the theory of completion of locally uniform spaces is developped in 1–5 of this paper.     

Multiplication groups of topological loops

In this paper, we discuss the question as to which Lie groups can occur as multiplication groups Mult(L) of connected topological loops L, and we describe the correspondence between the structure of the group Mult(L) and the structure of the loop L.     

On Perfect Matching Coverings and Even Subgraph Coverings

A perfect matching covering of a graph G is a set of perfect matchings of G such that every edge of G is contained in at least one member of it. Berge conjectured that every bridgeless cubic graph admits a perfect matching covering of order at most 5 (we call such a collection of perfect matchings a Berge covering of G). A cubic graph G is called a Kotzig graph if G has a 3‐edge‐coloring such that each pair of colors forms a hamiltonian circuit (introduced by R. Häggkvist, K. Markström, J Combin Theory Ser B 96 (2006), 183–206). In this article, we prove that if there is a vertex w of a cubic graph G such that , the graph obtained from by suppressing all degree two vertices is a Kotzig graph, then G has a Berge covering. We also obtain some results concerning the so‐called 5‐even subgraph double cover conjecture.     

关于格点覆盖的一个注记

对于一个给定椭球,本文给出了它的任一全等椭球都包含一个整点的一个充分必要条件.     

Coverings and Ring-Groupoids

We prove that the set of homotopy classes of the paths in a topological ring is a ring object (called ring groupoid). Using this concept we show that the ring structure of a topological ring lifts to a simply connected covering space.     

Coverings by minimal transversals

In this paper, we give counterexamples to the conjecture: “Every nonempty regular simple graph contains two disjoint maximal independent sets” [2, 7]. For this, we generalize this problem to the following: covering the set of vertices of a graph by minimal transversals. An equivalence of this last problem is given.     

Coverings of transfinite matrices

Subsets of a Cartesian product X × Y, where X and Y are arbitrary sets, are considered as a generalization of incidence matrices. Minimal cover, essential set etc. are introduced in a stronger sense and their properties discussed. The existence of a minimal cover for an arbitrary generalized incidence matrix is proved. As an application a previous result is extended.     

Indecomposable Coverings with Concave Polygons

We show that for any concave polygon that has no parallel sides and for any k, there is a k-fold covering of some point set by the translates of this polygon that cannot be decomposed into two coverings. Moreover, we give a complete classification of open polygons with this property. We also construct for any polytope (having dimension at least three) and for any k, a k-fold covering of the space by its translates that cannot be decomposed into two coverings.     

Zeta Functions of Graph Coverings

We give a decomposition formula for the zeta function of a group covering of a graph.     

Coverings by open cells

We prove that in a semi-bounded o-minimal expansion of an ordered group every non-empty open definable set is a finite union of open cells.     

Coverings of the smallest Paige loop

By investigating the construction of the split Cayley generalized hexagon, H(2), we get that there do not exist five distinct hexagon lines each a distance two apart from each other. From this we prove that the smallest Paige loop has a covering number of seven and that its automorphism group permutes these coverings transitively.     

有向图覆盖的Zeta函数

Mizuno和Sato定义了有向图的Zeta函数(见Linear Algebra Appl.,2001,336:181-190),它可用来计算有向图中具有给定长度的所有圈的个数.给出了任意有向图的覆盖的Zeta函数的计算公式.作为推论,覆叠重数为2,3和4的任意有向图覆盖(正则或非正则)的Zeta函数被计算出来,同时也计算了Cayley有向图的Zeta函数.     

Coverings of Groups and Types

Assume that G is a group covered by countably many sets X_n,n < . It is proved that G is generated in two or three stepsby a small number of the sets X_n. These results are generalizedfor countable coverings of types and countable colourings ofgraphs.