Fig. 2
From: The link between orthology relations and gene trees: a correction perspective
A species tree S and a DS-tree G which is S-consistent. The full orthology set induced by G is represented by the relation graph R. The graph \(R'\) is an example of a not satisfiable graph, as \(\{c_1, b_1, d_1, a_2\}\) induces a \(P_4\), while \(R''\) is an example of a satisfiable (it has no induced \(P_4\)), but not S-consistent graph (explanation is given in the text)