docs: def get_item_concept_mapping(self, lang):
          """ Get mapping of items_ids to concepts containing these items
  
          Args:
              lang (str): language of concepts
  
          Returns:
              dict: item (int) -> set of concepts (int)
  
          """
          concepts = self.filter(active=True, lang=lang)
          return group_keys_by_value_lists(Concept.objects.get_concept_item_mapping(concepts, lang))