def to_atomic(self):
        """
        Return the smallest atomic interval containing this interval.

        :return: an AtomicInterval instance.
        """
        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)
Return the smallest atomic interval containing this interval.

        :return: an AtomicInterval instance.