Fig. 6
From: A generalized Robinson-Foulds distance for labeled trees
An optimal path from T to T′ following Methodology 1 is depicted by black arrows and involves 6 operations. It is not optimal as another path, depicted by red arrows, involves only five operations. The path of length 3 from T to Ts acts on the safe edge, represented in orange. This path involves an edge contraction, an edge extension and a flip, leading to the good edge (red edge) in Ts