proposition: Fact many_app_app {P Qs Qs'} : many_app P (Qs ++ Qs') = many_app (many_app P Qs) Qs'.
proof: Proof. by rewrite /many_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