this paper, in particular, we analyze the earliest infalling population of satellites among which there are survivors at $z=0$. In the next paper we will present larger populations of dwarf galaxies which are accreted at later epochs.

We thus proceed in the following way. First of all, among subhaloes with bound masses greater than $10^8 M_{sol}$ at z = 0, the satellite with the earliest infall is identified. The adopted threshold mass ensures that we are considering well resolved objects, with at least $10^3$ particles (presumably their progenitors are even better resolved at higher redshift, before tidal mass loss begins), to minimize numerical effects on their internal dynamical evolution ([@1996ApJ...457..455M]). The object enters the host’s virial radius just before $z = 2$, when it is still unrelaxed, being the result of a merger between two subhalos. We trace the satellite back to $z = 2.87$ when the two progenitor merging subhalos are still well separated, namely their virial volumes do not overlap. Therefore the epoch corresponding to z = $2.87$ is set as the epoch of replacement of the original ErisDark’s infalling subhalos with their high resolution versions.\
Next we identify other subhalos that at this epoch are located between 