proposition: Lemma normal_Lambda k s: normal (Lambda k s) -> normal s.
proof: Proof. induction k; cbn; eauto using normal_lam_elim. Qed.
imports: List Arith Lia Morphisms FinFun Undecidability.HOU(std.std) Undecidability.HOU.calculus(prelim terms syntax semantics equivalence typing order confluence)