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Published online by Cambridge University Press: 03 October 2022
The diamond is the complete graph on four vertices minus one edge; $P_n$ and $C_n$ denote the path and cycle on n vertices, respectively. We prove that the chromatic number of a $(P_6,C_4,\mbox {diamond})$-free graph G is no larger than the maximum of 3 and the clique number of G.
This research was partially supported by a grant from the National Natural Sciences Foundation of China (No. 11971111).