proposition: Lemma ord'_app Gamma Gamma': ord' (Gamma ++ Gamma') = max (ord' Gamma) (ord' Gamma').
proof: Proof. induction Gamma; cbn; trivial. now rewrite IHGamma, Nat.max_assoc. Qed.
imports: List Arith Lia Undecidability.HOU(std.std) Undecidability.HOU.calculus(prelim terms syntax semantics typing)