
arXiv: 2108.00001
The reconfiguration graph for the $k$-colourings of a graph $G$, denoted $R_{k}(G)$, is the graph whose vertices are the $k$-colourings of $G$ and two colourings are joined by an edge if they differ in colour on exactly one vertex. For any $k$-colourable $P_4$-free graph $G$, Bonamy and Bousquet proved that $R_{k+1}(G)$ is connected. In this short note, we complete the classification of the connectedness of $R_{k+1}(G)$ for a $k$-colourable graph $G$ excluding a fixed path, by constructing a $7$-chromatic $2K_2$-free (and hence $P_5$-free) graph admitting a frozen $8$-colouring. This settles a question of the second author.
4 pages, 2 figures
FOS: Computer and information sciences, reconfiguration, Discrete Mathematics (cs.DM), frozen colouring, vertex colouring, Coloring of graphs and hypergraphs, 05C15, FOS: Mathematics, Mathematics - Combinatorics, Combinatorics (math.CO), Computer Science - Discrete Mathematics
FOS: Computer and information sciences, reconfiguration, Discrete Mathematics (cs.DM), frozen colouring, vertex colouring, Coloring of graphs and hypergraphs, 05C15, FOS: Mathematics, Mathematics - Combinatorics, Combinatorics (math.CO), Computer Science - Discrete Mathematics
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