Diagram of Nemesis method. (A) A particle is an individual object or a subsystem consisting of multiple individual objects. In this study, the individual objects are either stars or planets. (B) The gravitational force on a particle is the sum of the force from other particles [1] and the forces from the individual objects in the subsystems.(C) The gravitational force on individual objects is the sum of the force from the particles [1] and the forces from the other individual objects in the containing subsystem [2], but not from those individual objects in other subsystems [3]. The forces from A.1 and B.2 are each in a self-contained system and can be calculated in an N-body code; the forces in A.2 and B.2 are connected to the self-contained systems and are evolved with a leapfrog algorithm.