Extending fixed vertex-colourings to total colourings

Connectedness of the graph of vertex-colourings

For a positive integer k and a graph G, the k-colour graph of G, Ck(G), is the graph that has the proper k-vertex-colourings of G as its vertex set, and two k-colourings are joined by an edge in Ck(G) if they differ in colour on just one vertex of G. In this note some results on the connectivity of Ck(G) are proved. In particular it is shown that if G has chromatic number k ∈ {2, 3}, then Ck(G)...

Distant Set Distinguishing Total Colourings of Graphs

The Total Colouring Conjecture suggests that ∆ + 3 colours ought to suffice in order to provide a proper total colouring of every graph G with maximum degree ∆. Thus far this has been confirmed up to an additive constant factor, and the same holds even if one additionally requires every pair of neighbours in G to differ with respect to the sets of their incident colours, so called pallets. With...

Enumerating the edge-colourings and total colourings of a regular graph

In this paper, we are interested in computing the number of edge colourings and total colourings of a connected graph. We prove that the maximum number of k-edge-colourings of a connected k-regular graph on n vertices is k · ((k − 1)!). Our proof is constructive and leads to a branching algorithm enumerating all the k-edge-colourings of a connected k-regular graph in time O∗(((k − 1)!)) and pol...

Vertex-distinguishing proper edge colourings of some regular graphs

The vertex-distinguishing index χs(G) of a graph G is the minimum number of colours required to properly colour the edges of G in such a way that any two vertices are incident with different sets of colours. We consider this parameter for some regular graphs. Moreover, we prove that for any graph, the value of this invariant is not changed if the colouring above is, in addition, required to be ...

On conjectures on the defining set of (vertex) graph colourings