proposition: Fact many_ty_app_app {P ts ts'} : many_ty_app P (ts ++ ts') = many_ty_app (many_ty_app P ts) ts'.
proof: Proof. by rewrite /many_ty_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