chromatic number; connected graph; colouring of a graph; $k$-chromatic graphs; independent set
In this paper we characterize $k$-chromatic graphs without isolated vertices and connected $k$-chromatic graphs having a minimal number of edges.
 N. Christofides: Graph Theory - An Algorithmic Approach
. Academic Press, New York, 1975. MR 0429612
| Zbl 0321.94011
 A. Ershov, G. Kuzhukhin: Estimates of the chromatic number of connected graphs
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