Left: An undirected graph has $5$ vertices. The vertices are arranged in the form of an inverted pentagon. From the top left vertex, moving clockwise, the vertices are labeled: a$,$ b$,$ c$,$ d$,$ and e$.$ Undirected edges, line segments, are between the following vertices: a and b; a and c; b and c; c and d; e and d; and e and c$.$