Dynamical maps of the domain between the 2/1 and 4/3 MMRs, for two hypothetical systems composed of a solar mass star and two planets with masses m₁ = m₂ = 1.0 M_J (top panel) and m₁ = m₂ = 0.1 M_J (bottom panel). The secular angle Δϖ is fixed at 0 (positive values on the e₂-axis) or 180° (negative values on the e₂-axis). The light grey tones correspond to regions of regular motion, while the regions in blue correspond to highly chaotic motion. The location of several MMRs is indicated by vertical dashed lines. The solid lines mark the boundaries of the domains of mutually crossing planetary orbits.