A graph with vertex set V is said to be a graph on V . The vertex
et of a graph G is referred to as V (G), its edge set as E(G). These
conventions are independent of any actual names of these two sets: the
vertex set W of a graph H = (W; F) is still referred to as V (H), not as
W(H). We shall not always distinguish strictly between a graph and its
vertex or edge set. For example, we may speak of a vertex v 2 G (rather
than v 2 V (G)), an edge e 2 G, and so on.