Figure 2
From: Covariance of maximum likelihood evolutionary distances between sequences aligned pairwise
Possible topological relations of sequences. For two pairwise distances, one can distinguish three possible underlying topological configurations relating them. If they are estimated between four sequences, there are two possible configurations. Either they share some common evolution (a) or they are independent (b). In the third configuration, the two distances are estimated from two OPAs that share a sequence (c).