Figure 1.

Constraint graph, satisfiability and consistency. A constraint graph R = (V, E, U) with E and U depicted by solid and dotted edges, along with with two satisfiable realizations R₁ = R({d₁e₁}) and R₂ = R({d₁c₂}). The gene names correspond to their respective species in the species tree S. The tree G₁ is a DS-tree that satisfies R₁ while G₂ is a DS-tree that satisfies R₂. Duplication nodes in G₁ and G₂ are indicated by a green square. G₁ is not consistent with S because for instance, G₁ has the speciation triplet s(a₁)s(d₁)|s(e₁) = ad|e while S has the de|a triplet. The tree G₂ is consistent with S.