DS-maps on the (e₁, e₂) and (e₂, e₃) planes, where the family S₆ is projected, and the (∆ϖ₂₁, ∆M₂₁) and (∆ϖ₃₂, ∆M₃₂) planes. Kepler-51 is identified by the magenta “+” symbol, while the errors are delineated by magenta dashed lines. The color bar illustrates the DFLI values; dark colors correspond to regular evolution, while pale ones signify chaoticity. R_L indicates that both pairs of planets are locked in a two-body MMR (2/1 and 3/2 MMR), while R_S,L indicates the 1/1 secondary resonance inside the 2/1 MMR for the inner pair and a locking in the 3/2 MMR for the outer pair of planets.