“…(1)] at that point. 21,33 When these points are, in addition, related by the C 4 rotational symmetry, as is the case with X and Y points on the square lattice, the corresponding band inversions are connected to each other. If there is a band inversion at X point, there is one at Y point as well, and this is enforced precisely by the C 4 symmetry, 21 as it is the case in the X − Y phase, which is obtained in the model (1), as detailed below.…”