Frame (a): Projection of the grid 𝒢₂ onto the ${\overline{a}}_1-{\overline{e}}_1$ plane (pink crosses), which is the work domain for the computation of the action variable of ${\overline{H}}_a$. Red and yellow curves are taken from Fig. B.1. The gray curve is the level curve of I₁ = −0.017626 in Fig. 4(a). The two black curves mark approximately the boundaries where the black crosses have corresponding circles dwelling exactly on them in Fig. 5. The red, blue, and yellow curves are the level curve of σ_L = 5 × 10⁻⁶,4 × 10⁻⁶, 3 × 10⁻⁶. The yellow dot is taken from Fig. 4(c). Frame (b): Grid 𝒢₃ defined in Eq. (B.10) marked by black crosses.