The APE framework systematically explores available elementary processes by launching dimer TS searches 49 from a given initial structure. It thereby relies on a fuzzy classification algorithm (DECAF ) to categorize all atoms of the structure into groups with essentially equivalent local atomic environment. In order to establish a maximally diverse set of elementary processes and suppress re-discovery of already identified TSs, the TS searches are then performed centered on one randomly chosen representative of each such equivalence group In simpler systems, APE naturally terminates if all groups in the list are processed and no new local atomic environments are found. In the present system, new equivalence groups in system structures of increasingly higher energy are continuously discovered. We therefore stop the exploration when the energies of these structures continue to be 1 eV higher in energy than the initial structure. As motivated above, we aim for a first unbiased assessment of available low-energy elementary processes for the initial oxidation of the Pd surface. Processes that already start from initial states higher in energy than the barrier used to identify facile processes are therefore beyond the scope of the present study, though we emphasize that a continued oxidation may well have to go through such thermodynamic bottlenecks.