proposition: Lemma subst_exp_spec : forall e1 e2 x1, subst_exp e2 x1 e1 = open_exp_wrt_exp (close_exp_wrt_exp x1 e1) e2.
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