unfold RSym_sym.
induction i; intros; simpl in *;
destruct (as_tree tr) eqn:?; destruct_as_tree; solve_exprD; unfold none_reif; solve_exprD.
Qed.

Lemma get_reif_eq2 :
forall typ i tr tus tvs val,
exprD' tus tvs (typtree typ) tr = Some val ->
exprD' tus tvs (tyoption typ) (App (Inj (inr (Data (fget typ i)))) tr)  =
exprD' tus tvs (tyoption typ) (get_reif i tr typ) .