  Mergers of galaxies are extremely violent events shaping their evolution.
Such events are thought to trigger starbursts and, possibly, black hole
accretion. Nonetheless, it is still not clear how to know the fate of a galaxy
pair from the data available at a given time, limiting our ability to constrain
the exact role of mergers. In this paper we use the lightcone of the
Horizon-AGN simulation, for which we know the fate of each pair, to test three
selection processes aiming at identifying true merging pairs. We find that the
simplest one (selecting objects within two thresholds on projected distance $d$
and redshift difference $\Delta z$) gives similar results than the most complex
one (based on a neural network analyzing $d$, $\Delta z$, redshift of the
primary, masses/star formation rates/aspect ratio of both galaxies). Our best
thresholds are $d_\mathrm{th}\sim100\mathrm{\, kpc}$ and $\Delta z_\mathrm{th}
\sim 10^{-3}$, in agreement with recent results.
