code: def _is_mutated(self):
          
  
          mutated = self._mutated
          if self.children is not None:
              for child in self.children:
                  if isinstance(child, Sequence) or isinstance(child, SequenceOf):
                      mutated = mutated or child._is_mutated()
  
          return mutated
docs: :return:
              A boolean - if the sequence or any children (recursively) have been
              mutated