Super-period of planet f with respect to e (in red) and g (in black) for a set of first-order MMRs. The purple line indicates the value of the super-period (260 day) between the other pairs of the chain. Only two possible periods allowed planet f to be part of the resonant chain, which correspond to the near-intersection of the right-hand side of a red curve, the left-hand side of a black curve, and the horizontal purple line.