Resolution:
## Figure 1.
Definition of vectors for a polygonal curve. Definition of vectors used in the computation of the writhe number of two segments
of a polygonal curve. Points 1 and 2 define the first segment, and 3 and 4 the second.
The vectors r_{13}, r_{14}, r_{23}, and r_{24}, are translated so that they originate at the center of a unit sphere. The area A of the quadrangle they span is given by A = α+β+γ+δ-2π, where α is the size of the angle measured in radians.
Chang |