(a) Pair of TPs (red points) connected by a nodal line (red line) enclosed by a sphere. The arrows indicate the individual Wilson loops winding around the sphere. (b) Example of a trivial pair of TPs. (c) The Wilson loop spectrum on a sphere enclosing a pair of TPs. Two Wilson loop eigenvalues feature gapless flows (colored in red and blue). (d) The C₃ symmetry expectation value of individual Wilson lines. Figure reused from Ref. [21].