proposition: Lemma fv_exp_open_exp_wrt_exp_rec_lower : forall e1 e2 n1, fv_exp e1 [<=] fv_exp (open_exp_wrt_exp_rec n1 e2 e1).
proof: Proof. pose proof fv_exp_open_exp_wrt_exp_rec_lower_mutual as H; intuition eauto. Qed.
imports: Coq.Logic.FunctionalExtensionality Coq.Program.Equality Metalib.Metatheory Metalib.LibLNgen Stlc