Module unique := fc_unique wf subst.Module invert := fc_invert wf weak subst.Module erasem := erase wf weak subst ext_invert.

Lemma map_map : forall a1 x G2, map erase_sort (map (tm_subst_tm_sort a1 x) G2) = map (tm_subst_tm_sort (erase a1) x) (map erase_sort G2).