code: def get_to(self, ins):
          
          input_entities = set()
          attribute_values = set()
          for in_ in ins:
              if self.ATTRIBUTE not in self.entity_graph.has_a.get_descendants(in_.head.name):
                  attribute_values.update(in_.head.attributes[self.ATTRIBUTE])
                  input_entities.add(in_.head.name)
          if len(attribute_values) == 0:
              attribute_values = ins[0].head.attributes[self.ATTRIBUTE]
          elif len(attribute_values) > 1:
              raise ValueError('Unable to resolve single output attribute value for chromosome_id ({}),'.format(', '.join(attribute_values)))
          return list(attribute_values)[0]
docs: Resolve the output attribute value for 'chromosome_id'. Valid values are immutable, ie. the attribute key is not
          an actual entity. Mutable values will be changed to match the immutable value if unique. Otherwise an error is
          thrown.
  
          :param ins: iterable of input workflows
          :return: output attribute value