“…System (2) is topologically equivalent to dr dτ = r · R(y) = r⟨y, Q (y)⟩, (3) dy dτ = Q T (y) = ⟨y, y⟩Q (y) − ⟨y, Q (y)⟩y. (4) System (4) is an independent system on S 2 , which is important to us for analyzing the topology of (2) (see [3]). As definitions in [4], we write Γ , g, and C for trajectories, singularities, and closed orbits of (4), respectively, and W for trajectories of (2).…”