More generally, two graphs are the same if two vertices are joined by an edge in one
graph if and only if the corresponding vertices are joined by an edge in the other.
Another graph that is the same as the graphs in Figs. 1.3 and 1.4 is shown in Fig. 1.5.
Here all idea of space and distance has gone, although we can still tell at a glance
which points are joined by a road or a wire.