“…Motivated by a recent characterization of infinite-finite dualities by P. L. Erdős, Pálvölgyi, Tardif, Tardos [8], we introduce a notion of regular families of relational structures. These (possibly infinite) families of structures generalize regular forests, used in [8] to characterize infinitefinite dualities. In fact the regular families of trees (and forests) corresponds to well established notion of recognizable tree languages, see [5].…”