Returns just the upper and lower boundaries
        [upper, lower] representing the most general positive
        boundaries and the most specific lower boundaries

def get_boundaries(self):
        """
        Returns just the upper and lower boundaries
        [upper, lower] representing the most general positive
        boundaries and the most specific lower boundaries
        """
        if not self.__values_computed:
            self.__compute_values()
        return set(self.upper), set(self.lower)