This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
Paleyperfect.svg The Paley graph of order colored with three colors and showing clique of three vertices In this graph and each of its subgraphs the chromatic number equals the clique number so it is perfect graph en David Eppstein en David Eppstein original upload log page en Paleyperfect svg David Eppstein bytes no Paley