If a reference direction does not have any solution assigned to it after reaching the splitting front, then the molecule in the splitting front with the smallest perpendicular distance to this direction is selected for survival. If all underrepresented reference directions have been assigned one surviving solution, and the maximum size of the surviving population has not been reached, the remaining solutions are selected by a stochastic procedure. Note that NSGA-III selects the solutions in the fronts before the splitting front in its entirety, like in NSGA-II. However, contrary to NSGA-II's crowding distance which is calculated within the splitting front, the reference directions used in NSGA-III take into account the diversity of the entire surviving population.