code: def to_atomic(self):
          
          lower = self._intervals[0].lower
          left = self._intervals[0].left
          upper = self._intervals[-1].upper
          right = self._intervals[-1].right
  
          return AtomicInterval(left, lower, upper, right)
docs: Return the smallest atomic interval containing this interval.
  
          :return: an AtomicInterval instance.