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_istree :
forall i tus tvs t0 vr e t x,
exprD' tus tvs t0 (set_reif i vr e t) = Some x ->
t0 = typtree t.