proposition: Lemma fv_exp_open_exp_wrt_exp_lower : forall e1 e2, fv_exp e1 [<=] fv_exp (open_exp_wrt_exp e1 e2).
proof: Proof. unfold open_exp_wrt_exp; default_simp. Qed.
imports: Coq.Logic.FunctionalExtensionality Coq.Program.Equality Metalib.Metatheory Metalib.LibLNgen Stlc