Sketch of the on-the-fly cluster-finding scheme, illustrating different situations in which RsvPs become inert or active relative to the FoF time steps. RsvPs older than their t_dyn become active to form stars. The five rows represent the evolution of five distinct RsvPs, with each column indicating a particular simulation time step. Only those RsvPs that are activated before the next FoF time step, together with the newly formed stars whose ages are younger than τ_young, are included in the FoF cluster identification. See Section 3.3 for details.