Resonant structure indicated by χ² on the (e₁, e₂) plane for Case A. Four panels are for the two-body MMRs between (a) m₁ and m₂, (b) m₂ and m₃, (c) m₁ and m₃, and (d) the three-planet Laplace resonance with resonant angle φ₀. The large value of χ² (light colour) indicates that the resonant angle is in libration, while the small χ² (dark tones) indicates circulation. The narrow strip-like structure indicated by a black arrow in (a) divides the map into two parts, namely Region 1 and Region 2. Moreover, another narrow strip (indicated by the red arrow) can be seen in Region 2.