Therefore, if the bands are inverted but Equation ( ) is not satisfied, then the conduction and valence bands are single-valleyed at the point of inversion (Figure ). On the other hand, if the bands are inverted and Equation ( ) is satisfied, then the bands form ring-like edges around the point of inversion (Figure ). The threshold can be satisfied by increasing the degree to which the bands are inverted (i.e. by making M 0 more negative).