The evolution of nine-planet system during tidal decay of the host binary, with mutual planet–planet gravitational interactions included. The system parameters are taken from Figure 2, with e_b,0 = 0.8 as a fiducial value: the planets are ordered by increasing distance with semimajor axes a_p = 0.55 au, 0.72 au, 0.94 au, 1.24 au, 1.63 au, 2.13 au, 2.81 au, 3.69 au, 4.85 au. Mutual interactions lead to frequent planetary collisions, with some planets experiencing repeated collisions, e.g., O2 and O4 merge into O4﹩^{\prime} ﹩, O1 and O5 merge into O5﹩^{\prime} ﹩, and then O4﹩^{\prime} ﹩ and O5﹩^{\prime} ﹩ collide to form O5″.