proposition: Lemma close_exp_wrt_exp_open_exp_wrt_exp : forall e1 x1, x1 `notin` fv_exp e1 -> close_exp_wrt_exp x1 (open_exp_wrt_exp e1 (var_f x1)) = e1.
proof: Proof. unfold close_exp_wrt_exp; unfold open_exp_wrt_exp; default_simp. Qed.
imports: Coq.Logic.FunctionalExtensionality Coq.Program.Equality Metalib.Metatheory Metalib.LibLNgen Stlc