proposition: Lemma normal_AppR_left s T: normal (AppR s T) -> normal s.
proof: Proof. induction T in s |-*; cbn; eauto using normal_app_l. Qed.
imports: List Arith Lia Morphisms FinFun Undecidability.HOU(std.std) Undecidability.HOU.calculus(prelim terms syntax semantics equivalence typing order confluence)