The band inversion-induced warping effects illustrated in Figures and are rather idealized; in reality, the ring-like band edges are broken into a finite number of ellipsoidal pockets around the k-point where band inversion occurs (k0). The resulting valley degeneracy (i.e. number of pockets) is determined from the point group symmetry of k0. This is because band inversion leads to warping near k0, where the bands retain the same symmetry properties as k0 itself. As a result, a carrier pocket is mapped to equivalent points by the symmetries of k0, leading to the formation of multiple electronic valleys.