Schreir graphs: Transitivity and coverings

Bipartite Graphs and Coverings

In many real world applications, data are organized by coverings, not partitions. Covering-based rough sets have been proposed to cope with this type of data. Covering-based rough set theory is more general than rough set theory, then there is a need to employ sophisticated theories to make it more adaptive to real world application. The covering is one of core concepts in covering-based rough ...

Action graphs and coverings

Coverings of K-graphs

k-graphs are higher-rank analogues of directed graphs which were first developed to provide combinatorial models for operator algebras of Cuntz-Krieger type. Here we develop the theory of covering spaces for k-graphs, obtaining a satisfactory version of the usual topological classification in terms of subgroups of a fundamental group. We then use this classification to describe the C∗algebras o...

Transitivity conditions in infinite graphs

We study transitivity properties of graphs with more than one end. We completely classify the distance-transitive such graphs and, for all k ≥ 3, the k-CS-transitive such graphs.

Composite planar coverings of graphs

We shall prove that a connected graph G is projective-planar if and only if it has a 2n-fold planar connected covering obtained as a composition of an n-fold covering and a double covering for some n¿ 1 and show that every planar regular covering of a nonplanar graph is such a composite covering. c © 2002 Elsevier Science B.V. All rights reserved.