<a href="https://en.wikipedia.org/wiki/Edge_coloring" class="extiw" title="w:Edge coloring">Edge coloring</a> of an eight-vertex complete graph. Each of the seven color classes consists of one edge from the center to a polygon vertex, together with the three perpendicular edges connecting pairs of polygon vertices.
<a href="//commons.wikimedia.org/wiki/User:David_Eppstein" class="mw-redirect" title="User:David Eppstein">David Eppstein</a>
<span class="int-own-work" lang="en">Own work</span>