code: def _get_id2lower(id2lower, item_id, item_obj):
      
      if item_id in id2lower:
          return id2lower[item_id]
      lower_ids = set()
      for lower_obj in item_obj.get_goterms_lower():
          lower_id = lower_obj.item_id
          lower_ids.add(lower_id)
          lower_ids |= _get_id2lower(id2lower, lower_id, lower_obj)
      id2lower[item_id] = lower_ids
      return lower_ids
docs: Add the lower item IDs for one item object and the objects below them.