A cycle decomposition of a graph Γ is a set C of cycles of Γ such that every edge of Γ belongs to exactly one cycle in C. Such a decomposition is called arc-transitive if the group of automorphisms of Γ that preserve C setwise acts transitively on the arcs of Γ . In this paper, we study arc-transitive cycle decompositions of tetravalent graphs. In particular, we are interested in determining an...

It is shown that the graph QQ) C obtained from the 7 -cube QQ) by deletion of a perfect Hamming code C has a spanning self-complementary subgraph which is edge-transitive but not vertextransitive and also extremal among all the cube subgraphs which are square-blocking and codeavoiding. Our work uses combinatorial techniques involving orientations on the Fano plane and the resulting Steiner trip...

In a non-complete graph $Gamma$, a vertex triple $(u,v,w)$ with $v$ adjacent to both $u$ and $w$ is called a $2$-geodesic if $uneq w$ and $u,w$ are not adjacent. The graph $Gamma$ is said to be   $2$-geodesic transitive if its automorphism group is transitive on arcs, and also on 2-geodesics. We first produce a reduction theorem for the family of $2$-geodesic transitive graphs of prime power or...

Using covering graph techniques, a structural result about connected cubic simple graphs admitting an edge-transitive solvable group of automorphisms is proved. This implies, among other, that every such graph can be obtained from either the 3-dipole Dip3 or the complete graph K4, by a sequence of elementary-abelian covers. Another consequence of the main structural result is that the action of...

Let k ≥ 3 be a positive odd integer and q be a power of a prime. In this paper we give an explicit construction of a q–regular bipartite graph on v = 2q vertices with girth g ≥ k + 5. The constructed graph is the incidence graph of a flag–transitive semiplane. For any positive integer t we also give an example of a q = 2–regular bipartite graph on v = 2q vertices with girth g ≥ k + 5 which is b...

A characterization is given of a class of edge-transitive Cayley graphs, providing methods for constructing Cayley graphs with certain symmetry properties. Various new half-arc transitive graphs are constructed. © 2004 Elsevier Ltd. All rights reserved.

The complementary prism of a graph Γ is the ΓΓ̄, which formed from union and its complement Γ̄ by adding an edge between each pair identical vertices in Γ̄. Vertex-transitive self-complementary graphs provide vertex-transitive prisms. It was recently proved author that ΓΓ̄ core, i.e. all endomorphisms are automorphisms, whenever vertex-transitive, self-complementary, either core or complete graph. ...

We describe an implementation of Italiano's partially dynamic data structure for maintaining transitive closure information in a directed graph and report on experimental results with random directed graphs and random sequences of operations. The operations supported are edge insertions or edge deletions, and queries. For the case of edge deletions the directed graph is assumed to be acyclic.

A regular and edge-transitive graph which is not vertex-transitive is said to be semisymmetric. Every semisymmetric graph is necessarily bipartite, with the two parts having equal size and the automorphism group acting transitively on each of these parts. A semisymmetric graph is called biprimitive if its automorphism group acts primitively on each part. In this paper biprimitive graphs of smal...

A transitive decomposition of a graph is a partition of the edge set together with a group of automorphisms which transitively permutes the parts. In this paper we determine all transitive decompositions of the Johnson graphs such that the group preserving the partition is arc-transitive and acts primitively on the parts.