Fig. 2
From: Predicting horizontal gene transfers with perfect transfer networks
a A PPN network with one character c with two states \(\{0,1\}\). b A tree displayed by G that admits a labeling such that every state forms a connected component. Note that this tree can be obtained by the removal of the green edge and suppression of the resulting subdivision node. The interpretation of this scenario is that state 0 was transferred using the birectional edge. On the other hand, a solution for PTNs would forbid the transfer of state absence, and would also disregard the removal of the green edge, in which case no \(\mathcal {C}\)-labeling is possible