bt_shift_core_left
bt_shift_core_left(tree, node, idx, hdr->bth_count - idx,
bt_shift_core_left(tree, node, idx, hdr->bth_count - idx,
bt_shift_core_left(tree, neighbor, 1, r_hdr->bth_count,
bt_shift_core_left(tree, keep, new_idx, keep_hdr->bth_count - new_idx,