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On the chromaticity of certain subgraphs of a q-tree. (English) Zbl 0698.05029
It is known that the chromatic polynomial of triangulated graphs has only integral roots, but the converse doesn’t hold. The author gives here a new family of graphs for which the converse is also true. Namely, he proved that a graph G on \(n\geq q+1\) vertices (q\(\geq 2)\) has the chromatic polynomial \(P(G;\lambda)=\lambda (\lambda -1)...(\lambda -q+2)(\lambda - q+1)^ 2(\lambda -q)^{n-q-1}\) if and only if G is obtained from a q- tree on n vertices by deleting an edge contained in exactly q-1 triangles; furthermore such a graph is triangulated.
Reviewer: C.Radu

MSC:
05C15 Coloring of graphs and hypergraphs
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