From: Consistency of the Neighbor-Net Algorithm
Case
i
j
(i)
i = 1
1 ≤ j <r
(iv)
1 <i ≤ r
r ≤ j <n
(ii)
(v)
r <i <n
i ≤ j <n
(iii)
1 <i <r
i ≤ j <r