Analytical results for the resonant regions for apsidal resonances centred at σ_1,c = 0 (left panel) and the associated numerical results for the distribution of apsidal resonance (right panel). For the numerical results, the initial condition is g₀ = 0 and h₀ = 0 (corresponding to σ_1,c = 0 at the initial instant). In the left panel, level curves of the motion integral Σ₂ are presented as background. In the right panel, blue dots stand for resonant trajectories inside islands centred at i = 90°, and red dots show resonant trajectories occurring in low-eccentricity, low-inclination spaces.