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

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).