User blog comment:PsiCubed2/My own version of BMS/@comment-30846880-20181121133049

Regarding bad root selection, I think Buchholz Hydras (BH) works as same as BM2 and BM4, because the searching of the smaller label in the ancestors on the branch of the cut node in BH can be regarded as the bad root selection with upper-branch-removing method of the BM2 which Bubby3 explained in the previous blog post.

The difference between BH and pair sequence is the method of copying. BH fills the place of cut node in the copied bad part with a node labeled with zero. Pair sequence leaves there as it is.