Definition reflect tus tvs e (ty : typ)
 := @exprD _ _ _ Expr_expr_fs tus tvs e ty.

(* Specifications: *)
Lemma some_none: forall T v, @None T = Some v -> False.
Lemma as_tree_l : forall e t l o r, as_tree e = Some (inl (t, l, o, r)) -> e = (App (App (App (Inj (inr (Data (fnode t)))) l) o) r).
Lemma as_tree_r : forall e t, as_tree e = Some (inr t) -> e = (Inj (inr (Data (fleaf t)))).