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 set_reif_exprD :
forall tus tvs typ i vr e v ev,
exprD' tus tvs (typtree typ) e = Some ev ->
exprD' tus tvs typ vr = Some v ->
exists r, exprD' tus tvs (typtree typ) (set_reif i vr e typ) = Some r.