(** ** SR with finite types to SR *)

Lemma rewt_inv    (Sigma : finType) (R : srs Sigma) (x0 : list Sigma) y' :
rewt (trans_R R) (map (index (X:=Sigma)) x0) y' -> exists y, y' = (map (index (X:=Sigma)) y) /\ rewt' R x0 y.