proposition: Fact many_pure_app_app {M Ns Ns'} : many_pure_app M (Ns ++ Ns') = many_pure_app (many_pure_app M Ns) Ns'.
proof: Proof. by rewrite /many_pure_app fold_left_app. Qed.
imports: List Lia Undecidability.SystemF.SysF Undecidability.SystemF.Autosubst.syntax Undecidability.SystemF.Autosubst.unscoped Undecidability.SystemF.Util(Facts poly_type_facts pure_term_facts) ssreflect ssrbool ssrfun