Returns the list of "perfect" solid angles Each edge is given as a
        list of its end vertices coordinates.

def solid_angles(self, permutation=None):
        """
        Returns the list of "perfect" solid angles Each edge is given as a
        list of its end vertices coordinates.
        """
        if permutation is None:
            return self._solid_angles
        else:
            return [self._solid_angles[ii] for ii in permutation]