436354.fig.003a
(a)
436354.fig.003b
(b)
Figure 3: (a) A simple multicast network with two terminals has only one encoding node; (b) A feasible multicast network with two terminals has two encoding nodes. But it is not a simple multicast network, because if we delete (v1,v3) and (v2,v4), this multicast network is also feasible.