Definition: A graph G = (V(G), E(G)), consists of two finite sets:
V(G), the vertex set, of the graph, often denoted by V., which is non-empty set of elements
called vertices and E(G), the edge set of the graph, often denoted by E., which is a possibly
empty set of elements called edges, such that each edge e ∈ E is assigned an unordered pair of
vertices (u, v) called the end vertices of e.