proposition: Lemma lambda_free_not_lam s: lambda_free s -> ~ isLam s.
proof: Proof. now destruct 1. Qed.
imports: List Lia Arith Init.Wf Morphisms Program.Program Undecidability.HOU(concon.conservativity calculus.calculus) Undecidability.HOU.unification(systemunification nth_order_unification)