Base of the two-dome structure at z = 0 (i.e., the “two-oval structure” drawn with dashed lines) for the particular arrangement of the fourth source, x₄ = 0. Magnetic field lines with different connectivity are shown in red, magenta, blue, and cyan; these colors correspond to those in Fig. 1. The first (small) oval is separated in the domains D₂ and D₃ by the large oval. The domains D₁ and D₄ are outside the small oval and separated by the large oval, where D₁ is the outer region. Small circles at the intersection of the oval boundaries are the null points of the magnetic field, which are the footpoints of the separator.