confused about translation state update in CT_ICP_GN

[HeXu1]

Hi thanks for your excellent work.
I'm confused why the translation state update in CT_ICP_GN doesn't multiply "rotation_begin",just like "trajectory[index_frame].begin_t = trajectory[index_frame].begin_t + translation_begin;" of frame begin state,but not "trajectory[index_frame].begin_t =rotation_begin * trajectory[index_frame].begin_t + translation_begin;".Does this mean the translation update can be described by “rotation_begin” through iteration? and can you show some theory material for this thanks a lot!
Hope for your reply.