A network is
said to be traversable when it is possible to start at a node and
trace out the whole network without having to retrace any arc.
It is only possible to traverse a network if either (a) all its
nodes are of even order, in which case it can be traversed from
any point, finishing the traverse at the same point, or (b) just
two of its nodes are of odd order, in which case the traverse must
start at one end at the other.
